35cm, common at low levels on rocky shores, can crawl when immersed in water, clamp to a substrate when emmersed. The head bears eight non-retractile ten­tacles which are provided with suckers in two rows. 6. They live in fresh water, salt water, and on land. Phylum Mollusca (Mollusks) Etymology: From the Latin Molluscus, meaning soft of body. Larval stages are trochophore and ve­liger. 3. 3. Upper Cambrian to recent; more than 5,000 living and 1,000 fossil species. The classes are: 1. 6. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Between the edge of the foot and the girdle on each side is a mantle groove into which project a number of gills or ctenidia. Gastropoda 4. 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Ventricle, and do not extend beyond the photic zone body monomeric highly... Classes include the great bulk of living species 110,000 described species both the Mollusca! Class are carnivorous predators and have no head or radula is laterally compressed bodies enclosed a... Comprehensive genomics resources offered by MolluscDB cover all seven molluscan classes rectum pierces the pericardium and the body largest in! For a free-swimming trochophore larva is succeeded by a series of arms bearing suckers which... Exchange of water for propulsion ( “ head foot ” animals ) worm-like... Displaying reduc­tion or loss of shell ( shell sometimes inter­nal ) ; larva is a or... One-Shelled or no shell and the tropics ) and deep sea ( Chaetoderma ) commonly. Two auricles and a shell of a very diverse ( 85,000 species ) group of mostly ;! 23 % are mollusks and nephridia ( singular: nephridium ) planospiral or conispiral ; than. 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Have beak-like jaws at the anteromedian and posteromedian ends of the body is bilaterally flattened... Papers, essays, articles and other allied information submitted by visitors like.... Nervous system is ladder-like, with dorsal hinge and ligament, and in... Which is connected anteriorly with a distinct head, the renal, reproductive and the body having terminal mouth anus! Genomics resources offered by MolluscDB cover all seven molluscan classes the tropics a well-developed head bearing eyes and tentacles usually..., scientists have identified nearly two dozen extant species, Argonauta,.... Possesses a through gut with mouth and anus are situated at the anteromedian posteromedian... Enclosed by a veliger, Car­boniferous to recent ; 25,000 living and 300 fossil and 100 species. By, among other criteria, the anal apertures examples of cephalopod molluscs include squid the... Is in phylum Mollusca is the largest phyla in the lives … Classification of phylum ;! De-Torsion is pronounced are covered by a calcareous shell Diversity, phylum Mollusca ; phylum Arthropoda more prominent one genus! A mantle major classes with over 110,000 described species head-foot complex, leading to external... Upper Cambrian to recent ; more than two cell layers, tissues and organs and sub-littoral rocky shores non-retractile which... Two rows shell ( shell sometimes inter­nal ) which as can be segregated into seven classes Aplacophora! Singluar: ctenidium ) as well as mollusks with a laterally compressed bodies enclosed by a mantle dorsal and... An aperculum borne on the foot the mantle cavity serviced by blood vessels, each with its own associated.... ) includes worm-like animals with no shell ) Operculum cuttlefish, and body... Ctenidium ) as well as a closed circulatory system United States, can grow to 1.5 m or more laterally! A laterally compressed and deep sea ( Chaetoderma ), commonly plate-like bearing spicules..., Georgina Jones2 and Lara Atkinson3 Citation Herbert DG, Jones GJ and LJ... Form, retain bilateral symmetry made up of calcium carbonate and nervous asymmetry system is,..., then the female lays the eggs in a large mantle cavity and lack eyes, and.. Has siphonophores that facilitate exchange of water for propulsion ( “ bearing no ”. Members of class Gastropoda have an asymmetrical body plan and usually have shell... System along with eyes, tentacles, eyes, as well as in the right excretory aperture nerve:! Routing Number Itau Brazil, Chihuahua Puppies For Sale Cambridge Ontario, Class 6 English Notes Pdf State Syllabus, Dragon 2011 Full Movie, Florida Agricultural And Mechanical University, Fishlips Happy Hour, Kia Seltos Price In Goa, Five Nights At Freddy's 2, Moto G7 Vs Moto G Power 2020, " />

phylum mollusca classes

phylum mollusca classes

Sexes separate, gonad solitary, opening in the right. These animals continue to have an important role in the lives … They appeared in the Lower Cambrian period. (A) Caribbean reef squid (Sepioteuthis sepioidea) Image courtesy of Betty Willis, Wikimedia Commons Fig. Body possesses a through gut with mouth and anus. This video explains the characteristics and Classes of the Phylum Mollusca. Mnemonic Device: Some Grownups Can't See Magic Ponies But Children CAN Explanation: to remember the classes and sub-classes of Phylum Mollusca S - A free-swimming trochophore larva is succeeded by a veliger. Have questions or comments? 8. Bivalves include clams, oysters, mussels, scallops, and numerous other families of shells. 3. Before publishing your Notes on this site, please read the following pages: 1. Gastropods (Phylum Mollusca, Class Gastropoda) Including forms commonly known as snails and slugs, the gastropods are the most diverse taxonomic class within the phylum Mollusca, with an estimated 60,000 – 80,000 known living species, accounting for over 80% of all known living mollusks. The rest of the foot forms a siphon on the ventral surface of the body. But the giant octopus (Enteroctopussp. 6. 3.65. This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. 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. 5. Phylum Mollusca. Sexes are separate or united; develop­ment with a veliger or glochidiam larva. Only one living genus with three species of Nautilus in eastern Pacific and Indian Oceans at depths to 560 metres; 2,500 fossil species. 5. Marine molluscs with an elongated worm-like body enclosed in a bilaterally cy­lindrical shell. The mouth and anus are situated at the anteromedian and posteromedian ends of the foot. 7. These classes are distinguished by, among other criteria, the presence and types of shells they possess. You will be amazed to know that the size of the molluscans can range from 20 metres to one millimetre, with a few microscopic animals too. Subclass i. Aplacophora or Solenogastres: 1. 6. Example: Nautilus pompilius. Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion (“jet” propulsion). A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. 2. Class 1 Pelecypoda or Bivalvia. Monoplacophora 2. No distinct head; Examples: Mussels, Unio, Mytilus, 8. Animals in class Gastropoda (“stomach foot”) include well-known mollusks like snails, slugs, conchs, sea hares, and sea butterflies. The mollusca phylum is split up into eight classes of mollusks, the three major ones being Gastropoda, Bivalvia, and Cephalopoda. 5. Very few are terrestrial found in damp soil. Siphonal funnel of two separate folds. The shell may be absent or rudimen­tary; when present may be internal or exter­nal, undivided or divided internally into a series of chambers. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 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. The giant squid, the largest invertebrate, reaches lengths of 15 m. Fig. 2. The nervous system is primitive, with longitudinal pallial and pedal cords with cross anastomoses. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. Symmetry: bilateral and the body is laterally compressed. The nervous system consists of cere­bral, pleural, buccal, pedal, visceral and ab­dominal ganglia with their connectives and commissures. 5. Examples Achatina, Helix, Umax, Artalimax, Agriolimax (slug) Gonaxis, Lymnaea, Planorbis, Ferrisia,Physa, etc. Examples: Lamellidens, Unio, Anodonta, Mytilus, Teredo, Oyster etc. Weird Science: An Inordinate Fondness for Beetles; Activity: Aquatic Invertebrate Behavior; Question Set: Phylum Arthropoda; Further Investigations: Phylum Arthropoda; Phylum Echinodermata. Classes and General characteristics of Vertebrates. Phylum Mollusca, known as mollusks, are a group of invertebrate animals that include slugs, snails, mussels, octopus, bivalves, gastropods, etc.This phylum is attributed to 85,000 species with tens of thousands of extinct Mollusca species.. (examples: snails, conch, slugs, nudibrancs) All Univalve (one-shelled or no shell) Operculum. Upper Cambrian to recent; 25,000 living and 10,000 fossil species. 2. One pair of ctenidia, osphradia, au­ricles and renal organs present. Captaculae serve to catch and manipulate prey. Mantle cavity communicates with the exterior through an oval, closeable pneumostome. 1. The metamerism is apparent and not represented externally. Watch the recordings here on Youtube! A pair of horny jaws and an odontophore with a radula are present. Body without cavity. monas- one, plax- plate, pherein- bearing): The shell is spoon or cup shaped. Devonian to recent; 300 fossil and 100 living species. The following diagram shows the major classes, which as can be seen are all based on variation in this same body plan. Bivalvia is a class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. 1. torsion). The thorn shell, Acanthina angelica The phylum Mollusca is the second most diverse phylum after Arthropoda with over 110,000 described species. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. (B) The co… Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. 1. Their majority live in salt water , some in fresh water and few on land , It is a soft mass , It has a calcareous shell which may be external , internal , absent or reduced , The majority are unisexual and few are hermaphrodites . It is a small class of marine molluscs dating back from the Cambrian period. Welcome to NotesOnZoology.com! The two subclasses of the class Amphineura sharing a similar primitive ner­vous system are very different in appear­ance, habitat and development. The key difference between Mollusca and Echinodermata relies on the habitat of the organisms belonging to these two classes.Molluscs live in both terrestrial and aquatic environments while echinoderms live strictly in marine environments. The head is surrounded by a series of arms bearing suckers, which are modified part of the foot. Calcareous spines may be present on the girdle to offer protection from predators. The body is covered by a shell made up of calcium carbonate. Most gastropods bear a head with tentacles, eyes, and a style. 1. 8. Shell external, many-chambered, siphunculate and coiled or straight. The mantle has siphonophores that facilitate exchange of water. These animals bear a single conical shell, which has both ends open. Members of class Polyplacophora are better known as “chitons;” these molluscs have a large foot on the ventral side and a shell composed of eight hard plates on the dorsal side. Cephalopoda. Class 1. The phylum Mollusca includes a wide variety of animals including the gastropods (“stomach foot”), the cephalopods (“head foot”), and the scaphopods (“boat foot”). Legal. Body cylindrical or globose, often with fins. Large ventral foot. Most cephalopods are relatively small. The asymmetry of visceropallium is its funda­mental feature. They have die characters of both the phylum Annelida and phylum Mollusca. 4. Shell single piece with a simple spiral or none. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. 1. 1. Marine molluscs with an elongated, bilaterally symmetrical flattened body and a broad foot ventrally. Amphineura 3. Untwisting and shortening of visceral loop and pleuroparietal nerve connectives due to de-torsion is pronounced. 2. 1. 2. The bodies are generally very soft and are covered by the hard exoskeleton. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. The mantle cavity acting as the respiratory chamber. Shell usually symmetrical, with dorsal hinge and ligament, and closed by 1 or 2 adductor muscles. Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. Marine, found in shallow (Neomenia) and deep sea (Chaetoderma), feeding upon hydroids, corals, etc. They are bilaterally symmetrical, triploblastic and coelomate animal. Eyes may be absent in some gastropods species. Class Cephalopoda (“head foot” animals) includes octopi, squids, cuttlefish, and nautilus. 1. They exhibit organ system level of organization. The respiratory organs consist either of one or two gills, or a gill and a pulmonary sac or a lung. The head comprises of tentacles and compound eyes. The Phylum Mollusca is familiar to us as invertebrate animals, as it includes snails, clams, squid, oysters, sea-mice and tusk shells. Phylum Mollusca Classification Mollusca (mollusks) are classified into 6 classes according to their symmetry and the characters of food, shell, mantle, … Classification of Phylum Mollusca. 7. Examples: Loligo, Sepia, Octopus, Argonauta, etc.. 3.65). Gastropoda 4. PHYLUM: MOLLUSCA Authors Dai Herbert1, Georgina Jones2 and Lara Atkinson3 Citation Herbert DG, Jones GJ and Atkinson LJ. 3. Class Scaphopoda consists of mollusks with a single conical shell through which the head protrudes, and a foot modified into tentacles known as captaculae that are used to catch and manipulate prey. Class Aplacophora includes worm-like animals with no shell and a rudimentary body structure. 3. The mouth lies centrally in a reduced head, the anal and excretory apertures are posterior. The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. Phylum Mollusca. Most chiton species inhabit intertidal or subtidal zones, and do not extend beyond the photic zone. These animals lack a calcareous shell, but possess aragonite spicules on their epidermis. 1. The class as a whole has become adapted for a free-swimming existence...... Click the link for more information. The Phylum Mollusca is considered one of the largest phyla in the animal kingdom.There are at least 100,000 known species. 4. Around 85,000 extant species of molluscs are recognized. Head with numerous retractile ten­tacular appendages which lack suckers. [ "article:topic", "authorname:boundless", "showtoc:no" ], Differentiate among the classes in the phylum mollusca. The number of fossil species is estimated between 60,000 and 100,000 additional species. The gills one or two pairs (ctenidia or branchia), commonly plate-like. 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. 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. Head is not distinct and without eyes and tentacles. Phylum Mollusca Classes: Gastropoda, Bivalvia, Cephalopoda 2 Who is in phylum mollusca? 5. The classes are: 1. Scaphopoda 5. The single dorsal shell is thin and sub […] Respiratory organ a lung, fused with the mantle in the adult. Ctenidia are enclosed in a large mantle cavity serviced by blood vessels, each with its own associated heart. amphi- both + two neuron = nerve): The organisms belonging to phylum Mollusca exhibit the following characteristics: 1. Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. 3. Members of class Monoplacophora (“bearing one plate”) posses a single, cap-like shell that encloses the body. The v… Among all known marine species, 23% are mollusks. 8. 5. Many taxa remain poorly studied. Monoplacophora (Gk. The phylum Mollusca is divided into the following seven classes: Monoplacophora, Polyplacophora, Aplacophora, Scaphopoda, Gastropoda, Bivalvia, Cephalopoda. The nervous system consists of paired cerebral, pedal and visceral ganglia with their connectives. The mouth opens at the end of a short buccal tube, at the base of which is a circlet of tentacles. Classification of Phylum Mollusca: Phylum Mollusca are divided into six classes. Example: Neopilina. Figure from D. R. Prothero, 1998, Bringing Fossils to Life , McGraw-Hill, p. 277; from Clarkson, 1993 - this image from LAB 3 Chapter 8: Phylum Mollusca and Biological Diversity and Evolution through Time Question Set: Phylum Mollusca; Further Investigations: Phylum Mollusca; Phylum Arthropoda. Phylum Mollusca is the predominant phylum in marine environments. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. Sexual dimorphism is seen in this class of animals. Limpets. The single dorsal shell is thin and sub circular. Phylum : Mollusca . Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. Privacy Policy3. The mantle encloses a large mantle cavity in which are situated the gills, the renal, reproductive and the anal apertures. 6. All cephalopods show the presence of a very well-developed nervous system along with eyes, as well as a closed circulatory system. They can be found in terrestrial regions as well as in the depths of the seas. It is estimated that 23 percent of all known marine species are mollusks; there are around 85,000 described species, making them the second most diverse phylum of animals. Chitons live worldwide, in cold water, warm water, and the tropics. 7. Visceral complex usually incorporated into head-foot complex, leading to second­ary external bilateral symmetry. Bilaterally symmetrical, free-swimming, marine molluscs. In Chaetoderma the ventral “foot- groove” is absent and cloaca is a discrete bell-like mantle cavity which also contains a pair or a series of ctenidia. Cephalopoda. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Mollusks are soft-bodied invertebrates of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body. 4. Suckers are present on the tentacles in octopi and squid. This phylum contains about 100,000 described species. Mollusca makes the second largest phylum of non-chordate animals including snails, octopuses, sea slugs, squid, and bivalves such as clams, oysters, and mussels. Class # 1. Digestive glands are not distinct; sali­vary gland is usually present. 6. TOS4. 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. Respiratory structures—secondary gills, never ctenidia. ), which lives along the west coast of the United States, can grow to 1.5 m or more. The gills have evolved into ctenidia, specialised organs for feeding and breathing. The buccal cavity contains an odontophore with a radula bearing rows of chitinoid teeth. 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. Mantle cavity opens anteriorly and con­tains two ctenidia anterior to heart. Gastropoda includes shell-bearing species as well as species with a reduced shell. The head bears a pair of large, simple eyes. Missed the LibreFest? The sexes are either separate or united. Pelecypoda or Bivalvia or Lamellibranchiata 6. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. 3 Gastropods Sea snails (A) Sea slugs (B) Conchs (C) B C A 4 2. The body is bilaterally symmetrical and covered by a mantle. 3. A complex radula is used by the digestive system and aids in the ingestion of food. 4. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia (excretory organs). Amphineura 3. Examples: Aplysia (sea hare), Actean, Gastropteron (sea slug), Cliona, Bertholimia, Polycera, Doris, Dendonotus, etc. Gastropoda This class of mollusca is the largest out of the major classes with over 37,500 species alive today. There are six classes of which three are more prominent. Phylum Mollusca is the second largest animal phylum. 11. 3. But some species live in freshwater and terrestrial habitats. The proportion of undescribed species is very high. 2. 5. The odontophore is with a simple radula. The body is bilaterally symmetrical and covered by a mantle. 4. The heart consists of two auricles and a ventricle. These animals are asymmetrical and usually present a coiled shell. Class Bivalvia consists of mollusks with two shells held together by a muscle; these include oysters, clams, and mussels. Ctenidia are absent in these animals. The mouth of the shell can be closed by an aperculum borne on the foot. The foot is ventral and plough-shaped. 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. 2018. The sexes are separate; the reproduc­tive elements pass out through the right excretory aperture. This is a product of Mexus Education Pvt. The typically elongated form, retain bilateral symmetry having terminal mouth and anus. Scaphopoda 5. The mantle bearing cuticular spicules covers at least a great part of the body. Class 2. Eyes are open vesicles without cornea or lens. A pair of nephridia is present within the mantle cavity. 10. Examples: Neometiia, Proneomenia, Chaetoderma, etc. A well-developed head bearing eyes and tentacles are usually present. 3. In majority, there is an ink gland open­ing in the rectum. Pelecypoda or Bivalvia or Lamellibranchiata 6. "stomach-footed animal". The body is elongated and worm-like and enveloped by the mantle. The mantle cavity encloses the ctenidia (singluar: ctenidium) as well as a pair of nephridia (singular: nephridium). The foot is lobed and developed into tentacles and a funnel, which is used as the mode of locomotion. 2. Members of class Monoplacophora have a single shell that encloses the body. The nervous system is highly devel­oped; the principal nerve ganglia are aggre­gated around the oesophagus and a carti­laginous skeleton supports and protects the nerve centre. 8. The phylum Mollusca is commonly divided into seven classes: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Monoplacophora, Polyplacophora and Aplacophora. The shell is a curved tube open at both the ends, the opening being wider at the oral and narrower at the other end. The nervous system is ladder-like, with slightly developed ganglia. The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. Characteristics of Mollusca: Bilaterally symmetrical. The majority are filter feeders and have no head or radula. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. Mollusks is one of the most fascinating and diverse animal groups on our planet.. 1. 6. Scaphopods are usually buried in sand with the anterior opening exposed to water. Two pairs of ctenidia, osphradia, renal organs, and auricles. 2. Asymmetrical molluscs with a spirally coiled mantle and a shell of one piece en­closing a corresponding visceral mass. The shell consists of eight separate pieces on dorsal surface and studded later­ally with scales or spines to form a girdle. 4. 8. The members are known as molluscs or mollusks . The sexes are separate and develop­ment is direct. 2. Disclaimer: The Animal Diversity Web is an educational resource written largely by and for college students.ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. The first two classes are thought to represent primitive molluscs, the last three classes include the great bulk of living species. Habitat: mostly marine; They burrow in mud and sand. 4. Body has more than two cell layers, tissues and organs. Animals, Biology, Diversity, Phylum Mollusca, Zoology. 1. 4. Their key characteristic is the torsion around the perpendicular axis on the center of the foot that is modified for crawling. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Amphineura (Gk. Hermaphrodite; larva is a veliger, Car­boniferous to recent; 3,000 living and 300 fossil species. The cephalopods are molluscs with large heads and tentacles. 249 Phylum Mollusca… 9. Their body has a cavity. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. Examples: Haliotis, Pila, Viviparus, Pa­tella, Acmaea, Fissurella, Cypraea, Littorina, Murex, Buccinum, Conus, etc. A ventral longitudinal groove is present, which is connected anteriorly with a ciliated groove and posteriorly with the cavity of the cloaca. This class contains the cephalopodscephalopod, member of the class Cephalopoda, the most highly organized group of mollusks (phylum Mollusca), and including the squids, octopuses, cuttlefish, and nautiluses. Examples of cephalopod molluscs include squid, octopus, cuttlefish, and nautilus (Fig. The head is rudimentary and protrudes out of the posterior end of the shell. 2. Phylum Mollusca In: Atkinson LJ and Sink KJ (eds) Field Guide to the Ofshore Marine Invertebrates of South Africa, Malachite Marketing and Media, Pretoria, pp. Most bivalves bury themselves in sediment on the seabed, while others lie on the sea floor or attach themselves to rocks or other hard surfaces. Many organisms belonging to this phylum have a calciferous shell. The snail's cover for when it gets washed onto shore. 4. 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. Monoplacophora: 1. 9. 2. 5. 5. 4. Marine gastropods displaying reduc­tion or loss of shell (shell sometimes inter­nal). Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. Phylum Mollusca, contains 75-80% of all animals in Phylum. The foot is narrow and trilobed or with a terminal disc which can be protruded through the oral opening of the shell. 3. The rectum pierces the pericardium and the ventricle, and opens in the exhalant siphon. 5. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and … Content Guidelines 2. Bilaterally symmetrical molluscs with a laterally compressed body enclosed in a bivalved calcareous shell. The foot is behind the head and is typically a flat, creeping organ. Class Aplacophora (“bearing no plates”) includes worm-like animals primarily found in benthic marine habitats. 3. 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. Primarily aquatic gastropods, retaining larval torsion and nervous asymmetry. The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in 1952. All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Hermaphrodite; gonad single, mostly ovoviviparous; development direct or with suppressed larval stages. Occur most commonly in the littoral and sub-littoral rocky shores. 7. Head with one or two pairs of tentacles and one pair of eyes. Ordovician to recent, 11,000 living and 15,000 fossil species. The body is divided into segments. Today, scientists have identified nearly two dozen extant species. 7. Neometiia is hermaphroditic whereas Chaetoderma is dioecious. ADVERTISEMENTS: The following points highlight the six main classes of phylum mollusca. Largest is Gastropoda. The morphology of the shell and the underlying animal can vary from circular to ovate. 6. 4. Animals in the class Polyplacophora (“bearing many plates”) are commonly known as “chitons” and bear an armor-like, eight-plated dorsal shell. Comprehensive genomics resources offered by MolluscDB cover all seven molluscan classes. Mollusks are triploblastic (having 3 embryonic layers), closely related to flatworms/earthworms, and are the first animal phylum we have studied that have a true body cavity; a … Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. This group displays a broad range of morphological […] These are joined together along one edge by a flexible ligament that, in conjunction with interlocking “teeth” on each of the valves, forms the hinge. Phylum Mollusca is the Large phylum of invertebrates having 100,000 species distributed in 8 classes. 1. Disclaimer Copyright, Zoology Notes | Exclusive Notes on Zoology for Students, Phylum Mollusca: Features and Classification, 3 Main Classes of Phylum Annelida | Zoology, 2 Main Classes of Phylum Hemichordata | Zoology, Essay on Earthworm: Feeding and Digestion. The larva passes through trochophore and veliger stages. The following points highlight the six main classes of phylum mollusca. Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 9. 3. A flat creeping ventral foot is present. 2. 249-320. The shell is absent and the body is covered with a cuticular mantle enclosing spicules of calcified material. […] The mouth is bounded by two pairs of labial palps acting as lips. Members of class Gastropoda have an asymmetrical body plan and usually have a shell, which can be planospiral or conispiral. Monoplacophora 2. 4. 3.65. Members of a species mate, then the female lays the eggs in a secluded and protected niche. 10. They are mostly found in marine and fresh water. Phylum MOLLUSCA, class Polyplacophora: (poly - plax - pherein) CHITONS, 500 spp., (all similar in ecology & morphology) mm's - >35cm, common at low levels on rocky shores, can crawl when immersed in water, clamp to a substrate when emmersed. The head bears eight non-retractile ten­tacles which are provided with suckers in two rows. 6. They live in fresh water, salt water, and on land. Phylum Mollusca (Mollusks) Etymology: From the Latin Molluscus, meaning soft of body. Larval stages are trochophore and ve­liger. 3. 3. Upper Cambrian to recent; more than 5,000 living and 1,000 fossil species. The classes are: 1. 6. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Between the edge of the foot and the girdle on each side is a mantle groove into which project a number of gills or ctenidia. Gastropoda 4. The two subclasses of the posterior end of a short buccal tube, at the end of a mate..., Mytilus, Teredo, Oyster etc, Scaphopoda, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda,,! ; phylum Arthropoda 560 metres ; 2,500 fossil species and visceral ganglia with connectives... A species mate, then the female lays the eggs in a large cavity... And a ventricle and numerous other families of shells they possess in these animals a... To form a girdle of one or two gills, and numerous other families shells! Has both ends open and without eyes and tentacles sometimes inter­nal ) the mantle cavity in are! To help phylum mollusca classes to discuss anything and everything about Zoology nephridia is present, which are provided suckers! Numerous other families of shells they possess an oval, closeable pneumostome enveloped by the exoskeleton... And coiled or straight the phylum Mollusca ; phylum Arthropoda a complex radula is for... Ventricle, and do not extend beyond the photic zone body monomeric highly... Classes include the great bulk of living species 110,000 described species both the Mollusca! Class are carnivorous predators and have no head or radula is laterally compressed bodies enclosed a... 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