5.5: Phylum Mollusca - Biology

5.5: Phylum Mollusca - Biology

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The phylum Mollusca is defined by several special characteristics. These defining characteristics include a mantle with a mantle cavity, a shell (except where lost), visceral mass, foot, and radula. The odontophore is in the mouth of most mollusks and it supports the radula (a ribbon of teeth). More features of molluscs include bilateral symmetry, soft or unsegmented bodies, respiration via ctenidium, ganglia/nerve comprised nervous system, haemocoel body cavity, etc. [1].

“Anatomy of a Common Land Snail”, by Jeff Dahl [CC BY-SA 4.0]

Although when most people think of a mollusc they imagine a typical clam or snail with the shell on the exterior of the organism, there are actually variations of these characteristics. One example of this is the Flamingo Tongue. The Flamingo Tongue is a small marine snail. It is a fascinating organism, in that their mantle, when they are at rest, covers the outer shell on the exterior of the organism. When threatened the Flamingo Tongue will retract all of the exposed tissue back into the shell in a very interesting manner.

“Flamingo Tongue, 2018” by Alana Olendorf [CC by 4.0]


Chitons are the common name for species in the Class Polyplacophora. Chitons are considered more primitive in relation to other groups within the phylum such as bivalves or cephalopods. There are 8 dorsal plates lining the dorsal surface of these organisms. There are many primitive species of the class Polyplacophora that are still extant. However, only a few species of Monoplacophorans still exist in the world today.

“Dorsal side of chiton specimen under dissection microscope 2019” by Jason Charbonneau [CC by 4.0]


Gastropoda is a very diverse class of molluscs. The subclass Prosobranchia, are often identified by their coiled, cone shaped or tubular shells [1]. The mantel cavity is typically located on the anterior of the organism. Important distinctions of these organisms are the variations or the absence of radula. These organisms utilize Nephridia for excretion of nitrogenous waste. One characteristic of gastropods is the presence of a calcareous operculum. This structure acts as a shielded plate that protects the organism by covering the opening when it is retracted into its shell.

In the photo below, the dark oval in the center is the operculum. They are calciferous and rough to the touch, protecting the opening to the shell like a man-hole cover.

“Gastropod under dissection microscope” by Jason Charbonneau [CC by 4.0]


Nudibranchs are typically categorized as sea snails which lack shells. Often they are richly colored and captivating to the eye. Their magnificent beauty is the result of aposematism which is the bright coloration exhibited by these organisms that warns predators that they are toxic, distasteful or dangerous. The toxicity of these organisms differentiates from species to species, with some being exponentially more dangerous than others. Their toxicity is usually contingent upon their evolutionary specialization and their genus’s specific niche.

“Flabellina iodinea” by Jerry Kirkhart [CC by 2.0]


Class Bivalvia consists of molluscs that have two connected shells such as Oysters, Clams, Mussels, Scallops and many more. Most bivalves are enjoyed as delicacies, despite the fact that they are benthic level filter-feeders. As others in the phylum Mollusca, bivalves have a shell that is made up of deposits of Calcium Carbonate. These deposits are derived from substances in the water and harden over-time.

“Clam Shells” by Jason Charbonneau [CC by 4.0]

Visible among the many aspects of an open clam are the posterior and anterior adductor muscles. The function of these muscles is to hold the shell closed as a defense from predators. The strength of these muscles given their relative size is immense. The mantle is a layer of tissue that overlays the visceral mass of these organisms and is directly connected to the shell. The foot of the bivalve is directly responsible for its movement. The muscular foot will emerge when the shell is opened and pushes the organism along or into the benthos or substrate.


Cephalopods exhibit several similarities but also distinguishable differences from other molluscs. They sometimes exhibit a calcium carbonate shell. Squids and Octopus lack this feature, but the more primitive Nautilus does have this feature. Species in the Class Cephalopoda contain a large closed circulatory system and prehensile arms/tentacles that encompass a mouth, complete with a beak and radula. One of the most important evolutionary aspects of these organisms are their large complex eyes. These eyes are specialized for improved sight at depths where little ambient light reaches. The mantle of these organisms forms a sizable ventral cavity containing ctenidia. A portion of the mantle also forms a muscular funnel. Water is taken up and forced through these chambers under pressure creating a unique form of jet propulsion. There are over 900 living species of cephalopods that inhabit the world today.

“Nautilus shell” by Jason Charbonneau [CC by 4.0]

“Squid, December 9, 2013” [CC 0 Public Domain]


  1. Brusca, Gary J., Brusca, Richard C. 2003, Invertebrates 2nd ed. ISBN 0-87893-097-3

The information in this chapter in thanks to content contributions from Alana Olendorf and Jason Charbonneau

Phylum Mollusca: Characters and Classification (With Diagram) | Animals

They are mostly marine. Many, however, occur in fresh water and some even in damp soil.

The body of molluscs is un-segmented with a distinct head, muscular foot and visceral hump. Neopilina is a segmented mollusc.

They usually show bilateral symmetry. In some molluscs like Pila, due to torsion (twisting) during growth, the adults become asymmetrical.

Shell is secreted by mantle. It is made up of calcium carbonate. Shell may be external (e.g., most of molluscs), internal (e.g., slug, cuttle fish, squid) or absent (e.g., Octopus).

It is a thin, fleshy fold of dorsal body wall more or less covering the body. It encloses a space, which is called mantle cavity (= pallial cavity).

Single layered epidermis is usually ciliated. Muscles are un-striped and occur in bundles.

Coelom is greatly reduced. It is restricted to pericardial cavity (space around the fieart), and to small spaces within kidneys and gonads (testes and ovaries). Spaces amongst the viscera (soft organs) contain blood and form haemocoel.

9. Blood vascular system:

It is open type. It includes dorsal heart, arteries that open into sinuses (spaces) and veins. Blood is usually blue due to the presence of a copper- containing blue respiratory pigment called haemocyanin. Among the molluscs, cuttle fish are exceptional in having closed blood vascular system.

These are gills (cteoidia). Mantle and pulmonary sae (in semi-terrestrial form).

Excretory organs are one or two pairs of sac- like kidneys. Gills are also excretory in function. Ammonia is chief excretory matter.

The nervous system comprises paired cerebral, pleural, pedal and visceral ganglia joined by the nerve connectives and conumssures. Connectives con­nect dissimilar ganglia however, commissures connect similar ganglia

In many molluscs, eyes are present over stalks called ommatophores. Statocysts (balancing organs) may be present. Osphradium is present in some molluscs for testing chemical and physical nature of water.

The sexes are generally separate but some are hermaphrodite.

They are oviparous. The development is either direct or indirect (metamorphosis). When the development is indirect it includes a characteristic larva, liger, trochophore or glochidium. Asexual reproduction is absent.

(ii) Mantle may be surrounded by shell, and

(iii) Nervous system consists of cerebral, visceral, pleural and pedal ganglia.

Advancement over Annelids:

(i) Shell is present in many individuals,

(ii) In some forms, a lungs is present for pulmonary respiration, and

(iii) Better developed sense organs such as eyes, statocysts and osphradia.

Classification of Phylum Mollusca:

Phylum Mollusca are divided into six classes.

Class 1. Monoplacophora (Gk. monas- one, plax- plate, pherein- bearing):

The shell is spoon or cup shaped. They have die characters of both the phylum Annelida and phylum Mollusca.

Class 2. Amphineura (Gk. amphi- both + two neuron = nerve):

There is a present non-ganglionated nerve ring around mouth with two pairs of interconnected nerve cord.

Class 3. Scaphopoda (Gk. scapha- boat, podos-foot):

Shell is tubular and open at both ends.

Class 4. Gastropoda (Gk. gaster- belly, podos- foot):

Shell is made up of one piece.

The early embryo is symmetrical but during development the body twists showing torsion so that the body becomes asymmetrical. It includes the largest number of molluscs e.g., Pila, Umax, Cypraea (Cowrie), Helix (garden snail), Aplysia (sea hare), Doris (sea lemon), Limnaea, (pond snail), Planorbis, Patella (true limpet), Turbinella (Shankh), Creseis (Sea butterfly).

Class 5. Pelecypoda or Lamellibranchiate or Bivalvia (Gk. pelekus- hatchet Podos foot):

Shells is made up of two halves.

Unio, Mytilus (Sea mussel), Teredo SpwoS EnZ (razor shell or razor clam), Solen (razor fish or razor shell), Ostrea (edible oyster), Pecten (scallop), Pinctada (Pearl oyster).

Class 6. Cephalopoda (Gk. kephale- head, podos- foot):

Head and foot region combined and modified into a structure which has eyes and eight tentacles, hence the name cephalopod or ‘head foot’. Cephalopods are regarded at the top of invertebrates evolution in terms of learned behaviour they exihibit. Shell is external (Nautilus), internal (sepia) or absent (octopus).

Sepia, Loligo, octopus, nautilus, (pearly nautilus). Some cephalopods are the largest invertebrates.

Evolutionary Precursor of Molluscs:

A “living fossil” named Neopilina discovered in 1952 from the Pacific Ocean, shows metameric segmentation which is not a characteristic of molluscs. Neopilina has 8 pairs of muscles, 5 or 6 pairs of gills, and 5 pairs of nephridia.

Metameric segmentation and presence of the trochophore larva in both annelids and molluscs suggest that molluscs have descended from the annelids. Thus, the annelids are the evolutionary precursor of molluscs. Neopilina is a “connecting link” between Annelida and Mollusca.

Chiton-The coat of mail shell:

Chiton is marine and found attached to rocks by its foot the shell consists of a row of eight plates.

Dentalium— The Elephant’s tusk-shell:

It is a marine mollusc. Dentalium is found burrowing in sand. The shell is slightly curved, tubular and opens at both the ends. There are present filamentous tentacles called the captacula, which are useful in feeding.

Unio (Fresh Water Mussel):

It is found in rivers, lakes and ponds. The animal is omnivorous feeding on microscopic organisms. Its larva lives as parasite on fish. Its shell consists of two halves, called the valves. A whitish elevation in each valve is called umbo.

The lines of growth indicate the age of the individual. There are present two siphons posteriorly. It acts as scavenger and keeps water clean. Its shell yields an excellent quantity of lime the shells of the fresh water mussels are used in the manufacture of buttons.

It inhabits ponds, paddy fields, sometimes streams and rivers It is chiefly hetmvorous and feeds on aquatic plants like Pistia and Valusnena. It leads an amohibious life respiring by means of gill in water and by a pulmonary sac an and. Thus it is adapted for both aquatic and terrestrial life.

The mouth or aperture of the shell is closed by a flat and oval plate, the operculum. Pila has osphradium which is meant for testing chemical and physical nature of water. The buccal cavity of Pila contains a rasping organ, the radula, with transverse rows of teeth for cutting the grasses.

It is terrestrial and is abundantly found in gardens, cultivated lands and over damp soil. It is nocturnal and herbivorous. Shell is internal. It is a hermaphrodite animal. The slug is a plant pest. It damages seedlings, tender shoots and leaves.

It is a marine and a good swimmer. In male the left arm is spoon shaped and is called hectocotylized which is used to transfer sperms into the female. The shell is internal. A pear-shaped ink-sac containing the ink-like fluid is present.

When the animal is attacked ink-like fluid is ejected through the funnel to form a smoke cloud. Sepia is edible. Sepia ink obtained from this animal is used by artists. The shell of sepia is used as a source of calcium for pet birds.

Like Sepia, it is also found in the warm seas. It also ejects a dark ink to form a smoke cloud to escape from .the enemy. Its body resembles that of Sepia in form except that it is narrower than that of Sepia. It also has internal shell invertebrate is giant squid (Architeuthis) up to 18 meters long. LxAigo is edible. The giant squid has the largest eye in the animal kingdom.

It is also marine. It kills its prey with poisonous saliva. One of the arms of male is spoon shaped and is called hectocotylized which is used to transfer sperms into the female. The shell is absent. Octopus ejects an inky fluid in water and forms a screen for defence from its enemies. Octopus can change its colour.

Phylum Mollusca: General Characteristics and Its Classification

Mollusca makes the second largest phylum of non-chordate animals including snails, octopuses, sea slugs, squid, and bivalves such as clams, oysters, and mussels. This phylum contains about 100,000 described species. Among all known marine species, 23% are mollusks. But some species live in freshwater and terrestrial habitats. This group displays a broad range of morphological features such as a muscular foot, a mantle and visceral mass containing internal organs. Calcium carbonate secretes from the mantle and forms outer calciferous body shell in most of the mollusks. The size of the molluscans varies from less than one millimeter to 20 meters. They play an important role in the lives of humans because they are the source of food for many people as well as jewellery. Many molluscans are not good for human’s lives. Some cause diseases or acts as pests like the snails and slugs. Generally, the hard calciferous shells of mollusks are used to build awesome jewellery pieces. Some mollusks such as bivalves and gastropods produce valuable pearls. Natural pearls are produced when a small foreign object gets trapped in between the mollusk's body shell and mantle. Besides these, many scientists use bivalve mollusks as bioindicators of the freshwater and marine environments.

Phylum Mollusca Pdf

This is NOT what's on the test this is a summary of the major points from lab and lectures the lecture & lab notes are the sources of exam questions Synopsis of Phylum Mollusca (Molluscs) Identifying Characteristics of Phylum: -second largest phylum of animals in terms of number of known species -most versatile body plan of all animals -triploblastic with true coelom (eucoelomate. mollusca characteristics Phylum Mollusca is divided into eight classes, all but one of which are extant.A study of the type series of Nautilus pompilius Linnaeus, 1758 Mollusca, Cephalopoda, Nautilida SVETLANA V. NIKOLAEVA Preview PDF 100KB Full.Molluscs are soft bodied animals, often with hard shells for protection The animals belonging to the phylum Mollusca have soft-bodies, triploblastic and bilaterally symmetrical and coelomate. The study of Mollusca is called Malacology. They are sluggish invertebrates, with a thin fleshy envelope or mantle covering the visceral organs. The term Mollusca was derived from the term given by Aristotle to cuttlefish

Chapter 11 - Phylum Mollusca. Author links open overlay panel. Show more. Outline. Share. The Mollusca is well represented in freshwaters by two classes of molluscs Article Download PDF View Record in Scopus Google Scholar. Meier-Brook, 1983. C. Meier-BrookK Relationships of Mollusca Evolutionary hypotheses for the major groups of molluscs are controversial largely because of the extreme diversity in the phylum. Morphological hypotheses generally placed the Caudofoveata and Solenogastres as plesiomorphic based on their simple worm-like body plan and lack of a shell (Kocot et al., 2011)

Classes in Phylum Mollusca. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda View Phylum-Mollusca.pdf from BIO 1408 at Navarro College. Eucoelomates most invertebrate coelomates are protostomes animals having a true coelom are referred to as being eucoelomates i

Classification of Phylum Mollusca. There are six classes of which three are more prominent. Class 1 Pelecypoda or Bivalvia. Habitat: mostly marine They burrow in mud and sand. Symmetry: bilateral and the body is laterally compressed. No distinct head Examples: Mussels, Unio, Mytilus species in phylum Mollusca (35,000 are extinct) • The great morphological diversity is the result of elaboration on the basic body plan (HAM) HAM (Hypothetical Ancestral Mollusc) Digestive gland Mouth Radula Nerve collar Intestine Gill Anus Nephridium Shell Mantle Nerve cords foot coelom h e a r t gonads head View Mollusca Echinodermata.pdf from BIO 1A at Long Beach City College. Sonya Ontiveros Phylum Mollusca, soft body The molluscs are a very diverse group this phylum contains about 50,00 Phylum Mollusca 1. Kingodom AnimaliaPhylum Mollusca: MolluscsBy Natalia Ruggiero and Jacque OConnell 2. Structure soft bodied animals name from Latin word mollus meaning soft most are protected by a hard shell made of Calcium Carbonate have a reduced internal cell or have lost the shell completely during evolution. possession of a coelom coelom- a fluid-filled cavity that develops within the.

. Characteristics of Mollusca: Bilaterally symmetrical. Body has more than two cell layers, tissues and organs. Body without cavity. Body possesses a through gut with mouth and anus. Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. [ Phylum Mollusca 1. Snail Movement Marine snails such as Littorina littorea, L. obtusata, and L. saxatilus can be collected in the rocky intertidal year round. Refer to the photographs of the three species of Littorina in the MITZI Image Library. L. saxatilus lives in the upper rocky intertidal in rock crevices and may also be found in upper tide pools

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube PHYLUM : : MOLLUSCA GENERAL CHARACTERS : • Soft bodied triploblastic, bilaterally symmetrical, unsegmented schizocoelomates are - Molluscs • True coelomate unsegmented soft bodied animals-Mollusca• Study of mollusca - Malacology • Second largest phylum - Mollusca • Study of Molluscan shells - Choncology • Jhonson created the name Mollusca for - Cephalopods and barnacle Mollusca. Mollusks are soft bodied animals that have an internal or external shell, a similar body plan consisting of four basic parts: a foot, mantle, internal organs. Mollusks, and all higher phyla possess a . true coelom. (Eg pericardial cavity, and the cavity inside the gonad are coelomic - lined with mesoderm). Ingesting Food. y Phylum Mollusca - Class Cephalopoda In: Atkinson LJ and Sink KJ (eds) Field Guide to the Ofshore Marine Invertebrates of South Africa, Malachite Marketing and Media, Pretoria, pp. 321-391. 321 1 South African Department of Agriculture, Forestry and Fisheries, Cape Tow Chap. 04: Phylum: Mollusca Dr. Sharad V. Giramkar, Dept. of Zoology, Annasaheb Magar Mahavidyalaya Hadapsar, Pune-28 Content: 4.1 Introduction to Phylum Mollusca 4.2 Salient features of Phylum Mollusca 4.3 Classification of Phylum Mollusca with specific classes and mentioned examples (names only) Class: Gastropoda. e.g. Pila globosa (apple snail

(PDF) Chapter 18. Introduction to Mollusca and the Class ..

They use the Phylum Mollusca to undersand three major macroevolutionary patterns: divergent evolution, convergent evolution and coevolution. Grades: 7-12. There are high and middle school versions of each lab activity. Subjects: Biology, earth science, ecology, paleontology, evolutionary science Standards: See at the end of this document Phylum Mollusca - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online The group Mollusca, established by Cuvier (1798), com­prises of almost 1,00,000 species and is the second largest animal phylum (Fig. no larval stage Evolution of Molluscs new molecular evidence indicates an evolutionary relationship between Molluscs, Flatworms, Rotifers and Annelids Molluscs branched off the main animal line about 545 MY ago plant and animal life on land would not arise for. Mollusca is one of the most diverse groups of animals on the planet, with at least 50,000 living species (and more likely around 200,000). It includes such familiar organisms as snails, octopuses, squid, clams, scallops, oysters, and chitons ADVERTISEMENTS: In this article we will discuss about:- 1. Description of Torsion 2. Course of Torsion 3. Ways 4. Effect 5. Significance. Description of Torsion: 180° anticlockwise twisting of the visceropallium on the head-foot long axis during early development in gastropod mol­luscs is torsion. It is an early and fundamen­tal event in gastropod ontogeny (the [

Phylum Mollusca: Characters and Classification (With

The Animal Kingdom contains these seven Phyla: Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Arthropoda, and Chordata. The bodies of animals are made up of differentiated tissues to perform an equally specialized task, sometimes in to or three levels of differentiation (excluding sponges) css zoology most repeated on topic of Phylum Mollusca for competitive examination freely available to download for pdf expor Mollusca makes the second largest phylum of non-chordate animals including snails, octopuses, sea slugs, squid, and bivalves such as clams, oysters, and mussels. This phylum contains about 100,000 described species. Among all known marine species, 23% are mollusks. But some species live in freshwater and terrestrial habitats. This group displays a broad range of morphological [

Phylum Mollusca - Characteristics, Classification and Example

  • Mollusca represents the second largest animal phylum but remains poorly explored from a genomic perspective. While the recent increase in genomic resources holds great promise for a deep understanding of molluscan biology and evolution, access and utilization of these resources still pose a challenge
  • Fossils to ID 2016 - Set B.doc 1 of 8 12/4/2015 12:54:00 PM Phylum: Mollusca Phylum: Mollusca Class: Gastropoda Common Name or members: snails, nudibranchs, sea hares and garden slugs Habitat: All habitats: marine, freshwater, terrestrial Periods of Existence: Cambrian to Recent Description: Most Gastropod shells, especially from the Paleozoic, are preserved as interna
  • Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Mollusks have a dramatic variety of form, ranging from large predatory squids and octopus, some of which show a high degree of intelligence, to grazing forms with elaborately sculpted and colored shells
  • Phylum Mollusca Oant dam, Trðacna . External Food in mucous string Mouth Palp Shell Left mantle Excurrent flow Inqurrent flow Incurrent siphon Sand and debris Right mantle . Anterior aorta Digestive gland Stomach Anterior adductor Mouth Foot Nephridiopore Ventricle Auricle Kidney Pericardium Posterior aort
  • Phylum Mollusca Phylum comprendente animali invertebrati caratterizzati da un corpo molle non segmentato e, spesso, da una conchiglia calcarea con funzioni protettive. Sono primariamente marini. Sono divisi in 7 classi, 5 delle quali marine. Due grandi classi Gasteropoda e Bivalvia costituiscono il 95% di tutte le specie
  • Phylum Mollusca (mollis, soft) Over 90,000 living species 70,000 fossil species Some are herbivorous grazers Some are predaceous carnivores Many are filter feeders Some are parasites Mostly marine but some terrestrial and freshwater. Phylum Mollusca: Economics Many are used as foo

Phylum Mollusca - ScienceDirec

  1. g up of complexi­ties from simple to complex which can be marshalled into one perspective—the nerv­ous co-ordination. Prior to the description of the nervous system in different forms of Molluscs a basic plan of the Molluscan nerv­ous system is to be [
  2. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda.The members are known as molluscs or mollusks (/ ˈ m ɒ l ə s k /).Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high
  3. Phylum Mollusca • Includes snails and slugs, oysters and clams, and octopuses and squids. Bivalves Nautilu
  4. Phylum MOLLUSCA STYLOMMATOPHORA Vertigo moulinsiana (Dupuy, 1849). Pupa moulinsiana Dupuy, 1849.Cal. Extramar Galliae List., feb., p. 4. Vertigo Müller, 1774.Verm.

Molluscs. The phylum Mollusca is defined by several special characteristics. These defining characteristics include a mantle with a mantle cavity, a shell (except where lost), visceral mass, foot, and radula.The odontophore is in the mouth of most mollusks and it supports the radula (a ribbon of teeth). In many molluscs, it moves forward while the radula contacts the food, allowing the mollusc. The phylum Mollusca is the second largest in the animal kingdom including about 100,000 living species and with a long fossil record of some 35,000 more. The group is extremely diverse and includes such well known forms as the squid, octopus, slugs, snails and oysters Things to remember. Neopilina is considered as connecting link between Annelida and Mollusca. It is primitive with segmented body. 2 nd largest animal phylum after Arthropoda. Unio contains a digestive gland called Green gland, which is comparable to liver of vertebrates. Statocysts- for maintaining equilibrium of the body phylum mollusca class bivalvia zebra mussels-in 1986, zebra mussel veligers were introduced to the Great Lakes by the ballast water discharged from a northern European ship-the zebra mussel has spread from the great lakes to as far east as New York and as far south as Louisian

28.3F: Classification of Phylum Mollusca - Biology LibreText

  1. Phylum MOLLUSCA (1) Mięczaki gąbki parzydełkowce żebropławy typ budowy = bauplan Choanoflagellata Porifera Placozoa Cnidaria Ctenophora Sipunculata Echiura Mollusca Annelida Onychophora Arthropoda Tardigrad
  2. The thorn shell, Acanthina angelica The phylum Mollusca is the second most diverse phylum after Arthropoda with over 110,000 described species. Mollusks may be primitively segmented, but all but the monoplacophorans characteristically lack segmentation and have bodies that are to some degree spirally twisted (e.g. torsion)
  3. MAKALAH MOLLUSCA Diajukan guna memenuhi tugas mata kuliah Biologi Laut Dosen Pengampun : Intan Herwindra Brilianti Disusun oleh: HUSODO MUKTI (3213500005) PROGRAM STUDI BUDIDAYA PERAIRAN FAKULTAS PERIKANAN DAN ILMU KELAUTAN UNIVERSITAS PANCASAKTI TEGAL Halmahera KM. 1 - Tegal52122Telp./Fax. (1283) 351267 e-mail: [email protected] website: KATA PENGANTAR Puji syukur saya.

Phylum Mollusca - Phylum Mollusca soft bodied many with protective shell more species of molluscs in ocean than any other phylum, over 200,000 sp. the mantle is a thin tissue layer | PowerPoint PPT presentation | free to vie Mollusca composes the muckle phylum o invertebrate ainimals kent as the Molluscs. Mollusca is the second muckle maist phylum o the hale ainimal kinrick wi aroond 85,000 extant species o molluscs recognised.Molluscs is the mucklest marine phylum, comprisin aroond 23% o aa the named marine organisms.Numerous molluscs bide in freshwatter an terrestrial habitats as weel

Phylum-Mollusca.pdf - Eucoelomates most invertebrate ..

  • Multiple Choice Questions on Phylum Mollusca 1. Which of the following includes coelomate unsegmented organisms? a) Annelida. b) Molusca. c) Chordata. d) Arthropoda. 2. Head. Foot and visceral mass-this combination of characters is diagnostic of . a) Echinoderms. b) Arthropods. c) Molluscs. d) Annelida. 3. Internal shell is present in
  • phylum mollusca has. all mollusks- latin for soft. 3 classes of phylum mollusca. Gastropoda, bivalves Cephalopoda. all mollusks have. true coelom, soft body. all mollusks have 3 distinct body parts. foot, head, visceral mass. foot. muscular organ used for locomotion. head. contains sense organs
  • El phylum Mollusca representa a una gran diversidad de especies en el reino animal Zhi-Qiang (2011) estima 117 358 especies descritas en una clasificación evolutiva-descriptiva. Estos invertebrados poseen mayor número de especies que los vertebrados (64 832), en los que están incluidos los peces (31 000) y secunda a los artrópodos (
  • Mollusca are the second largest animal phylum on Earth after arthropods. The number of valid Recent species is currently estimated around 50,000 to 55,000 marine, 25,000 to 30,000 terrestrial and 6,000 to 7,000 freshwater. The number of fossil species is not known accurately, but is in.

Bathyal Mollusca from the cold-water coral biotope of Santa Maria di Leuca (Apulian margin, southern Italy). Zootaxa 4186(1): 1-97. DOI : 10.11646/zootaxa.4186.1.1 Phylum Mollusca Introduction Includes animals such as squids, snails, oysters, clams and slugs. Most are marine, but many are freshwater and some live on the land Despite the diversity of form and function among the molluscs, all members of this group have the same basic body plan Phylum Mollusca: Class Bivalvia. 75 likes · 17 talking about this. Medi Contoh anggota filum Mollusca adalah seperti, cumi-cumi, siput, remis, octopus, dan tiram (Karmana, 2007). Kurang lebih ada 100.000 spesies hewan yang tergolong phylum mollusca. Spesies tersebut memiliki peran yang cukup penting dalam kehidupan perairan laut. Hal ini karena peran Mollusca sebagai bioindikator di perairan (Jonh W Kimball, 1992) . Google Classroom Facebook Twitter. Correo electrónico. Animalia: Clasificación. Taxonomía y el árbol de la vida. Árboles filogenéticos. Reino Animalia: Phyla Porifera, Cnidaria, Ctenophora y Platyhelminthes

Mollusca (dalam bahasa latin, molluscus = lunak) merupakan hewan yang bertubuh lunak.Tubuhnya lunak dilindungi oleh cangkang, meskipun ada juga yang tidak bercangkang.Hewan ini tergolong triploblastik selomata. Ciri tubuh Ciri tubuh Mollusca meliputi ukuran, bentuk, struktur, dan fungsi tubuh. Ukuran dan bentuk tubuh Ukuran dan bentuk mollusca sangat bervariasi.Misalnya siput yang panjangnya. , Solanogastres, Chitons, Monoplacophorans, Scaphopods, Bivalves, Gastropods, Cephalopods) Common Name: Mollusks or molluscs Basic Animal Group: Invertebrate Size: Microscopic to 45 feet in length Weight: Up to 1,650 pounds Lifespan: Hours to centuries—the oldest is known to have lived over 500 year

Phylum Mollusca: General Characteristics and

  • PHYLUM MOLLUSCA Colwyn Sleep. GENERAL CHARACTERISTICS-Molluscs are free living forms and can aquatic, terrestrial, or amphibious.-Mollusk bodies are soft and unsegmented, enclosed in a mantle, and usually covered by a shell.-Mollusc digestive system is complete
  • PHYLUM MOLLUSCA gastropods, bivalves,cephelapods 3 GENERAL BODY REGIONS 1. head- with brain or sense organs 2. visceral mass- contains internal organs 3. foot- muscular part of bod
  • Phylum Mollusca Classes: Gastropoda, Bivalvia, Cephalopoda. HTML view of the presentation. Turn on screen reader support.
  • es symmetry. Some animals are asymmetrical which cannot be divided into two equal halves along any Arthropoda, Phylum Mollusca, Phylum Echinodermata, Phylum Hemichordata
  • Phylum Mollusca_Class Cephalopoda - Free download as Powerpoint Presentation (.ppt), PDF File (.pdf), Text File (.txt) or view presentation slides online. esrdtjb

INTRODUCTION. Mollusca, commonly known as shellfish, is the second largest phylum in the animal kingdom, with over 100 000 extant species. It also represents the largest marine phylum, containing ∼23% of all named marine organisms ().Molluscs are globally distributed and play vital roles in the structure and functioning of marine, freshwater and terrestrial ecosystems Mollusca Diversity. There are 4 classes in the phylum Mollusca: Class Polyplacophora- Chitins. Chitons are oval-shaped marine animals encased in an armor of eight dorsal plates Muscular foot acts like a suction cup to grip rock, radula used to scrape algae off the rock surfac The phylum consists of soft-bodied animals. The phylum Mollusca consists of a diverse group of organisms which include slow-moving snails and slug, bivalved clams, and highly active cephalopods. The phylum consists of over 50,000 living species Mollusca is a phylum of species that range from the cuttlefish to the sea snail. Species in the mollusca phylum reproduce either through external or internal fertilization. Internal fertilization occurs when the species functions as both sexes and is thus a hermaphrodite Download PDF's. Class 12 Class 11 Class 10 Class 9 Class 8 Class 7 Class 6. NCERT Easy Reading. Alleen Test Solutions. Blog. About Us. Career. Course. Mention the classes of the phylum Mollusca or Echinodermata. Give their distinguishing features and examples. 10:50 400+ LIKES. 600+ VIEWS. 600+ SHARES. Phylum Mollusca.

Mollusca Echinodermata

Phylum Mollusca Reproduction Most mollusks are dioecious, with external fertilization Most mollusks have a larval stage Depending on species, fertilization may - A free PowerPoint PPT presentation (displayed as a Flash slide show) on - id: 806c21-N2Nl PHYLUM: Mollusca CLASS: Bivalvia SUB-CLASS: Lamellibrachia FAMILY: Unionidae SPECIES: Villosa amygdala COMMON NAME: Freshwater mussel CODE: VILAMY DESCRIPTION: -Pronounced ridges with dark lines SIMILAR ANIMALS: Fingernail clam (rounder, smoother, transparent, lacks coloration) g SNAILS PHYLUM: Mollusca CLASS: Gastropoda SUB-CLASS: Prosobranch

Phylum Mollusca - SlideShar

  1. phylum Chordata deuterostome, eucoelomate, bilateral symmetry This phylum can be characterized by 4 unique characteristics found uniformly among members of the group, often referred to as the big four. Each of these is found in at least some stage of the life cycle of all members: 1. Notochord - cartilaginous skeletal rod 2
  2. Nervous System Shape Characteristics Movement exhibit bilateral symmetry and reduced segmentation mollusks are true coelomates with a reduced main body cavity called the hemocoel. mollusks are soft bodied, meaning they lack the rigid internal skeletal structure The nervous syste
  3. Domenico Fulgione » 10.Phylum Mollusca. Caratteristiche generali. Latino: molluscus = molle. Si conoscono circa 80.000 specie. Le dimensioni del corpo variano da 1 mm (piccoli gasteropodi) a circa 20 m (Architeuthis). Sono organismi Protostomi. La Metameria è presente solo in Neopilina (monoplacofori)
  4. Phylum Mollusca, Class Bivalvia - Bivalves are common shelled organisms like clams, oysters, and mussels which are generally filter feeders and live in or on top of the seafloor sediments. These are extremely common marine invertebrates today but less common as fossils the further back in geologic time you go
  5. 17/10/2009 19:51:35 Created by Systema Naturae 2000 Publisher 1.
  6. Mollusca •Phylum Mollusca includes snails and slugs, oysters and clams, and octopuses and squids •Most molluscs are marine, though some inhabit fresh water and some are terrestrial •Molluscs are soft-bodied animals, most are protected by a hard shell •Most molluscs have separate sexes with gonads located in the visceral mas

Mollusks: Ancient Wonders Of The Phylum Mollusca - Earth Lif

Phylum Mollusca Class Cephalopoda Subclass Nautiloidea The phylum Mollusca includes the familiar classes Gastropoda (snails), Pelecypoda (clams, oysters and scallops), and Cephalopoda (squids, octopuses, and the chambered Nautilus). This class is represented in the fossil record by members who built a hard outer shel Phylum Mollusca. Home Interesting Facts Contact Reproduction and Circulatory System Body Plan and Symmetry Shells Jokes for the Folks Body Plan and Symmetry The type of symmetry that mollusks have is bilateral symmetry. Meaning that the two sides are related. The. The phylum Mollusca is one of the three largest phyla of the animal kingdom. It contains about 100,000 living species, so that in abundance, the molluscs are second only to the Arthropoda

Zoology - Phylum Mollusca - YouTub

DOI: 10.3133/PP968 Corpus ID: 82516873. The paleontology of rostroconch mollusks and the early history of the phylum Mollusca @inproceedings, author=, year= <1976>Mammals: Phylum Mammalia 1. Hair 2. Mammary glands 3. Distinctive teeth 4. Highly developed brain 5. Extended care for the young Mammalian Origins 1. 200 million years ago, during the Triassic, synapsids gave rise to therapsids 2. Therapsids were the reptilian ancestors of mammals 3. The first mammals had evolved by the Jurassic The first Mammal

Phylum Mollusca Mollusca Bivalvia Free 30-day Trial

  • Zoological Studies 47(3): 338-351 (2008) Multi-Gene Analyses of the Phylogenetic Relationships among the Mollusca, Annelida, and Arthropoda Donald J. Colgan1,*, Patricia A. Hutchings2, and Emma Beacham1 1Evolutionary Biology Unit, The Australian Museum, 6 College St. Sydney, NSW 2010, Australia 2Marine Invertebrates, The Australian Museum, 6 College St., Sydney, NSW 2010, Australi
  • phylum .Mollusca About 50,000 species of mollusks have been described, making Mollusca the second largest phylum after Arthropods (or 3rd largest, if you divide Arthropods into 2 or more phyla, as some taxonomists do). Most mollusks have an internal or an external shell, a muscular foot,.
  • Princeton Universit
  • The Phylum Mollusca is familiar to us as invertebrate animals, as it includes snails, clams, squid, oysters, sea-mice and tusk shells. They live in fresh water, salt water, and on land. They appeared in the Lower Cambrian period. There are eight classes in this phylum, which are represented by over 150,000 living species and over 35,000.
  • II. Characteristics of Phylum Mollusca A. Contains nearly _____ living species and 35,000 fossil species. 1. This rivals the arthropods in diversity of body forms & sizes 2. Also rivals arthropods in terms of ecological success. a. Found in almost all environments: marine, freshwater, terrestrial B. Includes snails, slugs, clams

Phylum mollusca pdf - tamlytrilieu

  1. Phylum Mollusca Molluscs form a large part of the animal kingdom, comprising over fifty thousand known and described species. The phylum includes animals as varied as clams, oysters, squid and octopus, slugs and snails, and bivalves. Generally, combinations of the following characteristics are typical of molluscs
  2. Phylum Mollusca has been classified differently by different authors depending upon the characters of foot, mantle, shell, muscles, radula, nervous system and respira­tory organs. Ruppert and Barnes (1994), Meglitsch and Schram (1991) divided Molusca into 7 classes, while Parker and Haswell (1972), Morton and Yonge (1964) have clubbed class Aplacophora and Poly- placophora into a single class.
  3. phylum mollusca pdf notes December 1, 2020 / 0 Comments / in Uncategorized / by / 0 Comments / in Uncategorized / b
  4. Cephalopoda are addressed in a separate section due to the large number of species and their importance as a ishery. Mollusks - Block 1 Nabinger Purpose This lesson is intended to introduce the phylumMollusca and to go over its general physical characteristics. It inhabits ponds, paddy fields, sometimes streams and rivers It is chiefly hetmvorous and feeds on aquatic plants like Pistia and.
  5. Phylum Mollusca. Class . Polyplacophora. Class . Gastropoda. Class . Bivalvia. Class . Cephalopoda. More than 500,000 known species. chitons. Snails. Sea slugs.
  6. These 64 slides will provide your students with a solid lesson on the animals found in the Phylum Mollusca and their characteristics. Choose to use the traditional printable version, or the paperless, digital Google Apps version. The PowerPoint covers all the topics you would expect on mollusks f..

The mollusca - University of California Museum of Paleontolog

Phylum: Mollusca Gastropods, Bivalves & Cephalopods Mollusks Mollusks are soft-bodied animals that usually have an internal or external shell. Ex. Clams, squid, octopi, mussels, nudibranchs. They have a free swimming larval stage called a trochophore. Body Plan - 4 parts 1. foot - used for crawling, burrowing and tentacles 2 Mollusca. The Phylum Mollusca consists of approximately 85,000 different species. The organisms that make up the phylum are invertebrates.The work Mollusca derives from the Latin word mollis which means soft or flexible.The Mollusca excretory process involves a the organ of the kidney

Mollusca merupakan phylum terbesar kedua setelah Arthropoda yang memiliki sekitar 75 ribu jenis dan 35 ribu fosil yang muncul sejak zaman kambrium sampai sekarang. Mollusca telah menyebar pada setiap tempat hidup air dan hingga ke darat, hal ini menjadikan Mollusca sebagai jenis yang paling sukses hidup dari phylum lainnya sepanjang waktu geologi & dipercaya sebagai penentu untukIndeks Fosil Mollusca. Mollusca. Mollusks are a phylum that consists of predominantly marine animals as it takes up 23% of the animals in the water. Animals in this phylum include squid, cuttlefish, octopus, snails, slugs, etc. The molluscan nervous system consists of a pair of ganglia and nerve cords,. Question Set: Phylum Mollusca Further Investigations: Phylum Mollusca Phylum Arthropoda. Weird Science: An Inordinate Fondness for Beetles Activity: Aquatic Invertebrate Behavior Question Set: Phylum Arthropoda Further Investigations: Phylum Arthropoda Phylum Echinodermata. Voice of the Sea: Stella's Sea Urchins Voice of the Sea: Crown.

phylum mollusca pdf notes Uncategorised December 3, 2020 0 Comment December 3, 2020 0 Commen tinggi nilai suhu dan salinitas maka indeks keanekaragaman mollusca akan kecil, sedangkan semakin tinggi nilai pH dan kecerahan maka indeks keanekaragaman Mollusca akan semakin besar. Substrat pada rawa dampar yaitu berlumpur dan berpasir. Sumber belajar biologi yang dibuat berdasarkan keanekaragaman Mollusca di rawa Dampar berupa buku saku Los moluscos (Mollusca, del latín mollis blando) forman uno de los grandes filos del reino animal.Son invertebrados protóstomos celomados, triblásticos de simetría bilateral (aunque algunos pueden tener una asimetría secundaria) no segmentados, de cuerpo blando, desnudo o protegido por una concha.Los moluscos son los invertebrados más numerosos después de los artrópodos, e incluyen.

Torsion: Effect and Significance Phylum Mollusc

Whilst air conditioning does this quite well, there is still the issue of how to prevent the harmful UV rays and laboratory exercise 5 phylum mollusca pdf caused by bright sunlight from harming our small laboratory exercise 5 phylum mollusca pdf. In the past, it was common to have BMW rear windows tinted by a specialist tinting company Phylum Mollusca is the second largest phylum in the Animal kingdom. They play a very important role in the lives of humans. They are a great source of jewellery, food and other natural pearls. Explore more: M ollusca. Here are solved important MCQs on Mollusca, types and its importance. 1 This page was last edited on 3 December 2019, at 08:01. Files are available under licenses specified on their description page. All structured data from the file and property namespaces is available under the Creative Commons CC0 License all unstructured text is available under the Creative Commons Attribution-ShareAlike License additional terms may apply

Animalia and its Seven Phylum - The Classy Classification

I molluschi (Mollusca Cuvier, 1797) costituiscono il secondo phylum del regno animale per numero di specie dopo gli artropodi, con 85844 specie note. Sono animali primariamente marini, ma alcune specie hanno colonizzato le acque dolci come, ad esempio, i Bivalvi ed i Gasteropodi, ed alcune specie di questi ultimi si sono adattate anche all'ambiente terrestre Phylum Annelida and Phylum Arthropoda Today we will study the annelids, the segmented worms, and the arthropods, a huge group that contains insects, spiders, and crustaceans. Three tissue layers are present in both of these groups. Also, they share with molluscs the presence of a true coelom

Css zoology most repeated - Phylum Mollusc

Notes: Groups interested in participating in the LinkOut program should visit the LinkOut home page. A list of our current non-bibliographic LinkOut providers can be found here.. Disclaimer: The NCBI taxonomy database is not an authoritative source for nomenclature or classification - please consult the relevant scientific literature for the most reliable information Phylum Mollusca Mollusca มาจากภาษาละติน (molluscus = soft) แปลว่า นิ่ม หมายถึง ลำตัวนิ่ม จึงเรียก สัตว์ลำตัวนิ่ม ซึ่งมักจะมีเปลือก (shell).

Classification of Phylum Mollusca

Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Mollusks have a dramatic variety of form, ranging from large predatory squids and octopus, some of which show a high degree of intelligence, to grazing forms with elaborately sculpted and colored shells. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda.

Figure 2. This chiton from the class Polyplacaphora has the eight-plated shell that is indicative of its class. (credit: Jerry Kirkhart)

Class Aplacophora (“bearing no plates”) includes worm-like animals primarily found in benthic marine habitats. These animals lack a calcareous shell but possess aragonite spicules on their epidermis. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia (excretory organs). Members of class Monoplacophora (“bearing one plate”) posses a single, cap-like shell that encloses the body. The morphology of the shell and the underlying animal can vary from circular to ovate. A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in 1952. Today, scientists have identified nearly two dozen extant species.

Animals in the class Polyplacophora (“bearing many plates”) are commonly known as “chitons” and bear an armor-like eight-plated shell (Figure 2). These animals have a broad, ventral foot that is adapted for suction to rocks and other substrates, and a mantle that extends beyond the shell in the form of a girdle. Calcareous spines may be present on the girdle to offer protection from predators. Respiration is facilitated by ctenidia (gills) that are present ventrally. These animals possess a radula that is modified for scraping. The nervous system is rudimentary with only buccal or “cheek” ganglia present at the anterior end. Eyespots are absent in these animals. A single pair of nephridia for excretion is present.

Figure 3. These mussels, found in the intertidal zone in Cornwall, England, are bivalves. (credit: Mark A. Wilson)

Class Bivalvia (“two shells”) includes clams, oysters, mussels, scallops, and geoducks. Members of this class are found in marine as well as freshwater habitats. As the name suggests, bivalves are enclosed in a pair of shells (valves are commonly called “shells”) that are hinged at the dorsal end by shell ligaments as well as shell teeth (Figure 3). The overall morphology is laterally flattened, and the head region is poorly developed. Eyespots and statocysts may be absent in some species. These animals are suspension feeders—they eat material, such as plankton, that is suspended in the water around them. Due to their diet, this class of mollusks lacks a radula. Respiration is facilitated by a pair of ctenidia, whereas excretion and osmoregulation are brought about by a pair of nephridia. Bivalves often possess a large mantle cavity. In some species, the posterior edges of the mantle may fuse to form two siphons that serve to take in and exude water.

One of the functions of the mantle is to secrete the shell. Some bivalves like oysters and mussels possess the unique ability to secrete and deposit a calcareous nacre or “mother of pearl” around foreign particles that may enter the mantle cavity. This property has been commercially exploited to produce pearls.

Animals in class Gastropoda (“stomach foot”) include well-known mollusks like snails, slugs, conchs, sea hares, and sea butterflies. Gastropoda includes shell-bearing species as well as species with a reduced shell. These animals are asymmetrical and usually present a coiled shell (Figure 4). Shells may be planospiral (like a garden hose wound up), commonly seen in garden snails, or conispiral, (like a spiral staircase), commonly seen in marine conches.

Figure 4. (a) Snails and (b) slugs are both gastropods, but slugs lack a shell. (credit a: modification of work by Murray Stevenson credit b: modification of work by Rosendahl)

The visceral mass in the shelled species displays torsion around the perpendicular axis on the center of the foot, which is the key characteristic of this group, along with a foot that is modified for crawling (Figure 5). Most gastropods bear a head with tentacles, eyes, and a style. A complex radula is used by the digestive system and aids in the ingestion of food. Eyes may be absent in some gastropods species. The mantle cavity encloses the ctenidia as well as a pair of nephridia.

Figure 5. During embryonic development of gastropods, the visceral mass undergoes torsion, or counterclockwise rotation of anatomical features. As a result, the anus of the adult animal is located over the head. Torsion is an independent process from coiling of the shell.

Can Snail Venom Be Used as a Pharmacological Painkiller?

Figure 6. Members of the genus Conus produce neurotoxins that may one day have medical uses. (credit: David Burdick, NOAA)

Marine snails of the genus Conus (Figure 6) attack prey with a venomous sting. The toxin released, known as conotoxin, is a peptide with internal disulfide linkages. Conotoxins can bring about paralysis in humans, indicating that this toxin attacks neurological targets. Some conotoxins have been shown to block neuronal ion channels. These findings have led researchers to study conotoxins for possible medical applications.

Conotoxins are an exciting area of potential pharmacological development, since these peptides may be possibly modified and used in specific medical conditions to inhibit the activity of specific neurons. For example, these toxins may be used to induce paralysis in muscles in specific health applications, similar to the use of botulinum toxin. Since the entire spectrum of conotoxins, as well as their mechanisms of action, are not completely known, the study of their potential applications is still in its infancy. Most research to date has focused on their use to treat neurological diseases. They have also shown some efficacy in relieving chronic pain, and the pain associated with conditions like sciatica and shingles. The study and use of biotoxins—toxins derived from living organisms—are an excellent example of the application of biological science to modern medicine.

Class Cephalopoda (“head foot” animals), include octopi, squids, cuttlefish, and nautilus. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. All cephalopods show the presence of a very well-developed nervous system along with eyes, as well as a closed circulatory system. The foot is lobed and developed into tentacles, and a funnel, which is used as their mode of locomotion. Suckers are present on the tentacles in octopi and squid. Ctenidia are enclosed in a large mantle cavity and are serviced by large blood vessels, each with its own heart associated with it the mantle has siphonophores that facilitate exchange of water.

Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion. This is called “jet” propulsion. A pair of nephridia is present within the mantle cavity. Sexual dimorphism is seen in this class of animals. Members of a species mate, and the female then lays the eggs in a secluded and protected niche. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. Cephalopods such as squids and octopi also produce sepia or a dark ink, which is squirted upon a predator to assist in a quick getaway.

Reproduction in cephalopods is different from other mollusks in that the egg hatches to produce a juvenile adult without undergoing the trochophore and veliger larval stages.

In the shell-bearing Nautilus spp., the spiral shell is multi-chambered. These chambers are filled with gas or water to regulate buoyancy. The shell structure in squids and cuttlefish is reduced and is present internally in the form of a squid pen and cuttlefish bone, respectively. Examples are shown in Figure 7.

Figure 7. The (a) nautilus, (b) giant cuttlefish, (c) reef squid, and (d) blue-ring octopus are all members of the class Cephalopoda. (credit a: modification of work by J. Baecker credit b: modification of work by Adrian Mohedano credit c: modification of work by Silke Baron credit d: modification of work by Angell Williams)

Figure 8. Antalis vulgaris shows the classic Dentaliidae shape that gives these animals their common name of “tusk shell.” (credit: Georges Jansoone)

Members of class Scaphopoda (“boat feet”) are known colloquially as “tusk shells” or “tooth shells,” as evident when examining Dentalium, one of the few remaining scaphopod genera (Figure 8).

Scaphopods are usually buried in sand with the anterior opening exposed to water. These animals bear a single conical shell, which has both ends open. The head is rudimentary and protrudes out of the posterior end of the shell. These animals do not possess eyes, but they have a radula, as well as a foot modified into tentacles with a bulbous end, known as captaculae. Captaculae serve to catch and manipulate prey. Ctenidia are absent in these animals.

In Summary: Phylum Mollusca

Phylum Mollusca is a large, marine group of invertebrates. Mollusks show a variety of morphological variations within the phylum. This phylum is also distinct in that some members exhibit a calcareous shell as an external means of protection. Some mollusks have evolved a reduced shell. Mollusks are protostomes. The dorsal epidermis in mollusks is modified to form the mantle, which encloses the mantle cavity and visceral organs. This cavity is quite distinct from the coelomic cavity, which in the adult animal surrounds the heart. Respiration is facilitated by gills known as ctenidia. A chitinous-toothed tongue called the radula is present in most mollusks. Early development in some species occurs via two larval stages: trochophore and veliger. Sexual dimorphism is the predominant sexual strategy in this phylum. Mollusks can be divided into seven classes, each with distinct morphological characteristics

Phylum Mollusca

There are about 110 000 species of molluscs, varying in size from less than 1 mm to 1.3 m in the giant clam (Tridacna sp.) the giant squid (Architeuthis sp.), with tentacles 20 m long, is the largest known invertebrate. They are softbodied animals which gain support from a hydrostatic skeleton, but most have an internal or external shell. They possess a mantle, a covering of the body wall which lines the shell and secretes the calcium carbonate which constitutes the shell. Most molluscs are aquatic, but some live in damp terrestrial habitats. Molluscs are protostomes.

A radula is characteristic of most molluscs: this hard, chitinous strip bearing teeth is used as a file or a drill to aid foodgathering. Mollusc shells are well preserved as fossils: monoplacophorans and bivalves are known from the middle Cambrian univalves and cephalopods from the upper Cambrian. Octopuses are found in the late Cretaceous, but squids are found only in Tertiary rocks. It is thought, on the basis of their embryology, that the Mollusca and the Annelida may share a common ancestor, although features such as intracellular digestion, external cilia and the architecture of the nervous sytem may point to closer links with the Platyhelminthes.

Molluscs are triploblastic, coelomate animals which are, at least in their early development, bilaterally symmetrical. The body is unsegmented. The body comprises a head-foot and a visceral mass. The foot is a large, muscular organ used, in many forms, for locomotion or burrowing. In the cephalopods it is extended to form arms and tentacles. The visceral mass contains the major internal organs. The coelom is much reduced, but the cavities of the open circulatory system are greatly expanded to form the major enclosed body cavity, termed a hemocoel (cf. Arthropoda). In cephalopods, there is no large body cavity as the circulatory system is closed.

The gut is complete, with a mouth and an anus. Bivalves and some snails are sedentary filter-feeders: the gills are covered by mucus which traps food particles. Cilia waft the mucus to the mouth many molluscs have a style which is rotated by cilia to pull food-laden mucus into the gut. Chitons, slugs and snails use their toothed radulae to file at algae and other foodstuffs. Large molluscs such as squids may be active, macrophagous predators.

In many species of molluscs the foot is used for creeping or burrowing cephalopods expel water from the mantle cavity to permit jet-propulsion.

The hemocoel is the main component of the molluscan hydrostatic skeleton. In many species the shell gives additional support.

The cavity beneath the shell may contain the gills (ctenidia) or, in many terrestrial univalves, is vascularized to form a ‘lung’. Respiration is through the body surface (which may be extended to form respiratory tufts), by gills (ctenidia) in the mantle cavity or directly through vascularized mantle cavity surface layers. The hemocoel cavities contain blood in an open circulatory system (in cephalopods the hemocoel is reduced to permit a closed, high-pressure vascular system) there is a dorsal heart.

Excretion is by ‘kidneys’ or metanephridia which drain the coelom.

Except in bivalves, there is extensive cephalization, and sense organs include statocysts (for balance), head tentacles, paired eyes and osphradia which act as rheoreceptors monitoring water flow through the mantle cavity. The nervous system comprises paired pedal cords and visceral cords which unite anteriorly to form a cerebral ganglion or ‘brain’. The cephalopod nervous sytem is arguably the most sophisticated of all invertebrate nervous systems.

In most molluscs, the sexes are separate and external fertilization occurs in water land snails and nudibranch univalves are hermaphrodite, although they do not normally self-fertilize. Some oysters can reverse their sex from male to female and back, according to the season. The gonads are found near the pericardial coelom. In primitive molluscs, the gametes exit via the excretory ducts, but more advanced forms have complex gonoducts and other copulatory apparatus.

The egg usually hatches to form a trochophore larva which metamorphoses into a veliger larva, but in many marine snails the egg hatches to form a veliger, while the eggs of cephalopods and land snails bypass the larval stage todevelop directly into miniature adults. Some octopuses show parental care of eggs, clams may brood their young and some periwinkle snails are viviparous. Embryonic development follows a protostome pattern.

There are five classes of mollusc: Monoplacophora, Polyplacophora, Gastropoda, Bivalvia and Cephalopoda.

The little-known monoplacophorans are candidates for being the nearest living relatives to molluscan ancestors. There is a single shell plate with an anteriorly directed, peaked apex. The mantle cavity, containing a series of paired gills, forms grooves on either side of the broad foot. There is a radula and a simple digestive system. An example is Neopilina sp.

The 500 species of chitons are considered to have diverged early from the ancestral molluscan line. The body retains its bilateral symmetry, and the nervous and digestive systems are simple. The trocophore larva is similar to that of an annelid. The shell consists of a series of eight overlapping, anterior–posterior arranged plates. Chitons are marine herbivores which graze algae from rocks with their rasping radulae locomotion is by ripples or waves in the muscles of the foot. An example is Chiton divaceous.

The gastropods are typically aquatic, but some pulmonate gastropods live on land, mainly in damp places, although desert snails (e.g. Sphincterochila sp.) which can estivate during drought periods within their shells are known. The shell, where present, comprises one piece or valve. The foot is used for pedal creeping using antagonistic muscles creating ripples of contraction. Cephalization is notable, with eyes and tentacles present. There is a radula. Within the shell which is often coiled is a visceral mass. Unisexual and hermaphrodite species exist. The classification of the gastropods is controversial three orders are usually recognized:

(1) Prosobranchiata (e.g. whelks, limpets). These include most gastropods. The majority are marine. The gills are contained within the mantle cavity in front of the heart. The shell may be closed by an operculum. The sexes are usually separate. An example is Nucella lapillus (dog whelk).

(2) Opisthobranchiata (e.g. sea-hares, sea-slugs, sea-butterflies). These marine gastropods have a reduced or absent shell. The single gill lies posterior to the heart or may be absent. Most are carnivores living near to the seashore a few species swim. An example is Aplysia sp. (sea-hare).

(3) Pulmonata (e.g. snails, slugs). These freshwater and terrestrial gastropods lack gills and respire through a richly vascularized mantle cavity. Shells may be reduced or absent in slugs. They lack an operculum, although a temporary epiphragm may be secreted during a drought. They are usually hermaphrodite herbivores. Examples are Helix spp. (land snails).

Bivalves are usually marine but there are many freshwater species. The two, hinged valves of the shell can enclose the body completely. Cephalization may be very reduced, with sense organs and the radula being lost. Gills are enlarged and possess ciliary tracts used for filter-feeding: water is passed over the gills by ciliary action – water enters via the shell gap or through an inhalant syphon it may leave via an exhalant syphon. The foot can be used for burrowing (enzymes to digest lignin and cellulose in wood can, for example, be secreted) or it may be reduced. Powerful adductor muscles close the shell. The sexes are usually separate. Examples are Ostrea sp. (oyster) Mya sp. (clam) Anodonta sp. (swan mussel) Mytilus sp. (mussel).

These advanced marine molluscs are active carnivores: they are swimmers or bottom-livers. The head has a radula and there are usually large, sophisticated eyes with an architecture similar to that found in vertebrates. The foot is modified to form a funnel and tentacles (with suckers) around the mouth. There may be one or two pairs of gills within the mantle cavity. The shell is large and chambered in Nautilus sp. and in the extinct ammonites. In most living cephalopods, it is internal (cuttlefishes and squids) or absent (octopuses). A high-pressure, closed vascular system with capillaries is present, resulting from a reduced hemocoel: there is no large body cavity. Locomotion is by jetpropulsion as water drawn into the mantle cavity is forceably expelled via the syphon. Examples include Nautilus sp. Loligo sp. (squid).

Watch the video: 15 Phylum Mollusca Presentation (February 2023).