Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion (“jet” propulsion). 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. 7. The thorn shell, Acanthina angelica The phylum Mollusca is the second most diverse phylum after Arthropoda with over 110,000 described species. Respiratory organ a lung, fused with the mantle in the adult. Amphineura 3. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 2. Limpets. Head with numerous retractile ten­tacular appendages which lack suckers. The head is rudimentary and protrudes out of the posterior end of the shell. Visceral complex usually incorporated into head-foot complex, leading to second­ary external bilateral symmetry. The organisms belonging to phylum Mollusca exhibit the following characteristics: 1. The mollusca phylum is split up into eight classes of mollusks, the three major ones being Gastropoda, Bivalvia, and Cephalopoda. The buccal cavity contains an odontophore with a radula bearing rows of chitinoid teeth. 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. All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. 3. 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. 2. 5. Class Cephalopoda (“head foot” animals) includes octopi, squids, cuttlefish, and nautilus. [ "article:topic", "authorname:boundless", "showtoc:no" ], Differentiate among the classes in the phylum mollusca. Classification of Phylum Mollusca: Phylum Mollusca are divided into six classes. The first two classes are thought to represent primitive molluscs, the last three classes include the great bulk of living species. Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. Scaphopods are usually buried in sand with the anterior opening exposed to water. A ventral longitudinal groove is present, which is connected anteriorly with a ciliated groove and posteriorly with the cavity of the cloaca. Members of class Monoplacophora (“bearing one plate”) posses a single, cap-like shell that encloses the body. 1. Marine, found in shallow (Neomenia) and deep sea (Chaetoderma), feeding upon hydroids, corals, etc. Primarily aquatic gastropods, retaining larval torsion and nervous asymmetry. 3.65. The foot is narrow and trilobed or with a terminal disc which can be protruded through the oral opening of the shell. 7. This phylum contains about 100,000 described species. 2. 1. 8. Mollusca makes the second largest phylum of non-chordate animals including snails, octopuses, sea slugs, squid, and bivalves such as clams, oysters, and mussels. Missed the LibreFest? 2. Monoplacophora 2. Watch the recordings here on Youtube! 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. 2. Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Content Guidelines 2. Monoplacophora: 1. Pelecypoda or Bivalvia or Lamellibranchiata 6. Many organisms belonging to this phylum have a calciferous shell. The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in 1952. Their body has a cavity. Siphonal funnel of two separate folds. Occur most commonly in the littoral and sub-littoral rocky shores. Mnemonic Device: Some Grownups Can't See Magic Ponies But Children CAN Explanation: to remember the classes and sub-classes of Phylum Mollusca S - The two subclasses of the class Amphineura sharing a similar primitive ner­vous system are very different in appear­ance, habitat and development. 8. The body is elongated and worm-like and enveloped by the mantle. The classes are: 1. The larva passes through trochophore and veliger stages. The nervous system consists of paired cerebral, pedal and visceral ganglia with their connectives. The head is surrounded by a series of arms bearing suckers, which are modified part of the foot. Animals, Biology, Diversity, Phylum Mollusca, Zoology. 10. The mouth is bounded by two pairs of labial palps acting as lips. 6. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. The Phylum Mollusca is considered one of the largest phyla in the animal kingdom.There are at least 100,000 known species. Examples of cephalopod molluscs include squid, octopus, cuttlefish, and nautilus (Fig. 3. 5. 10. The asymmetry of visceropallium is its funda­mental feature. The following diagram shows the major classes, which as can be seen are all based on variation in this same body plan. Phylum Mollusca (Mollusks) Etymology: From the Latin Molluscus, meaning soft of body. The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. 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. 6. 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 . The mantle bearing cuticular spicules covers at least a great part of the body. 6. Weird Science: An Inordinate Fondness for Beetles; Activity: Aquatic Invertebrate Behavior; Question Set: Phylum Arthropoda; Further Investigations: Phylum Arthropoda; Phylum Echinodermata. The shell is absent and the body is covered with a cuticular mantle enclosing spicules of calcified material. 3. Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. 4. A flat creeping ventral foot is present. Sexual dimorphism is seen in this class of animals. Most gastropods bear a head with tentacles, eyes, and a style. Members of a species mate, then the female lays the eggs in a secluded and protected niche. Gastropoda includes shell-bearing species as well as species with a reduced shell. Class 1. The v… Monoplacophora 2. Marine gastropods displaying reduc­tion or loss of shell (shell sometimes inter­nal). Legal. Eyes may be absent in some gastropods species. Gastropoda This class of mollusca is the largest out of the major classes with over 37,500 species alive today. They are mostly found in marine and fresh water. The cephalopods are molluscs with large heads and tentacles. Examples: Lamellidens, Unio, Anodonta, Mytilus, Teredo, Oyster etc. 8. The sexes are separate and develop­ment is direct. The single dorsal shell is thin and sub […] Two pairs of ctenidia, osphradia, renal organs, and auricles. 249 Class # 1. Example: Nautilus pompilius. The head bears a pair of large, simple eyes. The bodies are generally very soft and are covered by the hard exoskeleton. Their key characteristic is the torsion around the perpendicular axis on the center of the foot that is modified for crawling. 1. Phylum Mollusca… One pair of ctenidia, osphradia, au­ricles and renal organs present. They live in fresh water, salt water, and on land. Cephalopoda. 6. Comprehensive genomics resources offered by MolluscDB cover all seven molluscan classes. Phylum Mollusca is the second largest animal phylum. This video explains the characteristics and Classes of the Phylum Mollusca. 7. They have die characters of both the phylum Annelida and phylum Mollusca. Body cylindrical or globose, often with fins. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. 1. 4. Shell external, many-chambered, siphunculate and coiled or straight. The class as a whole has become adapted for a free-swimming existence...... Click the link for more information. Shell single piece with a simple spiral or none. (A) Caribbean reef squid (Sepioteuthis sepioidea) Image courtesy of Betty Willis, Wikimedia Commons Fig. 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. 1. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. Body possesses a through gut with mouth and anus. 5. These animals continue to have an important role in the lives … 9. Class Aplacophora includes worm-like animals with no shell and a rudimentary body structure. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. 1. The odontophore is with a simple radula. They exhibit organ system level of organization. Body without cavity. The mouth lies centrally in a reduced head, the anal and excretory apertures are posterior. Very few are terrestrial found in damp soil. The body is bilaterally symmetrical and covered by a mantle. A free-swimming trochophore larva is succeeded by a veliger. Body has more than two cell layers, tissues and organs. Example: Neopilina. The head comprises of tentacles and compound eyes. Calcareous spines may be present on the girdle to offer protection from predators. 9. 4. The body is bilaterally symmetrical and covered by a mantle. 1. Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. The mantle encloses a large mantle cavity in which are situated the gills, the renal, reproductive and the anal apertures. Most cephalopods are relatively small. 3.65. 5. Sexes are separate or united; develop­ment with a veliger or glochidiam larva. 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. But some species live in freshwater and terrestrial habitats. "stomach-footed animal". ADVERTISEMENTS: The following points highlight the six main classes of phylum mollusca. […] 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. Upper Cambrian to recent; 25,000 living and 10,000 fossil species. Examples: Aplysia (sea hare), Actean, Gastropteron (sea slug), Cliona, Bertholimia, Polycera, Doris, Dendonotus, etc. 4. All cephalopods show the presence of a very well-developed nervous system along with eyes, as well as a closed circulatory system. Monoplacophora (Gk. 5. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. 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. 1. These animals lack a calcareous shell, but possess aragonite spicules on their epidermis. The foot is behind the head and is typically a flat, creeping organ. Class 2. 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 … The nervous system consists of cere­bral, pleural, buccal, pedal, visceral and ab­dominal ganglia with their connectives and commissures. TOS4. Ctenidia are enclosed in a large mantle cavity serviced by blood vessels, each with its own associated heart. The respiratory organs consist either of one or two gills, or a gill and a pulmonary sac or a lung. A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. These classes are distinguished by, among other criteria, the presence and types of shells they possess. 8. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. Chitons live worldwide, in cold water, warm water, and the tropics. Larval stages are trochophore and ve­liger. Examples: Neometiia, Proneomenia, Chaetoderma, etc. 5. The phylum Mollusca includes a wide variety of animals including the gastropods (“stomach foot”), the cephalopods (“head foot”), and the scaphopods (“boat foot”). Upper Cambrian to recent; more than 5,000 living and 1,000 fossil species. Examples Achatina, Helix, Umax, Artalimax, Agriolimax (slug) Gonaxis, Lymnaea, Planorbis, Ferrisia,Physa, etc. 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. The shell consists of eight separate pieces on dorsal surface and studded later­ally with scales or spines to form a girdle. Classes and General characteristics of Vertebrates. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. (examples: snails, conch, slugs, nudibrancs) All Univalve (one-shelled or no shell) Operculum. 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. This is a product of Mexus Education Pvt. Today, scientists have identified nearly two dozen extant species. 5. Members of class Gastropoda have an asymmetrical body plan and usually have a shell, which can be planospiral or conispiral. Have questions or comments? Gastropoda 4. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. A well-developed head bearing eyes and tentacles are usually present. These animals are asymmetrical and usually present a coiled shell. The proportion of undescribed species is very high. This group displays a broad range of morphological […] 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. (B) The co… Pelecypoda or Bivalvia or Lamellibranchiata 6. They are bilaterally symmetrical, triploblastic and coelomate animal. 249-320. The phylum Mollusca is commonly divided into seven classes: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Monoplacophora, Polyplacophora and Aplacophora. Untwisting and shortening of visceral loop and pleuroparietal nerve connectives due to de-torsion is pronounced. It is a small class of marine molluscs dating back from the Cambrian period. The shell is a curved tube open at both the ends, the opening being wider at the oral and narrower at the other end. These animals bear a single conical shell, which has both ends open. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. The gills one or two pairs (ctenidia or branchia), commonly plate-like. Class Aplacophora (“bearing no plates”) includes worm-like animals primarily found in benthic marine habitats. The heart consists of two auricles and a ventricle. Ctenidia are absent in these animals. The body is covered by a shell made up of calcium carbonate. In majority, there is an ink gland open­ing in the rectum. The Phylum Mollusca is familiar to us as invertebrate animals, as it includes snails, clams, squid, oysters, sea-mice and tusk shells. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and … 2. The single dorsal shell is thin and sub circular. 8. There are six classes of which three are more prominent. 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. The nervous system is primitive, with longitudinal pallial and pedal cords with cross anastomoses. They have a rudimentary mantle cavity and lack eyes, tentacles, and nephridia (excretory organs). Only one living genus with three species of Nautilus in eastern Pacific and Indian Oceans at depths to 560 metres; 2,500 fossil species. 1. 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. 3. The head bears eight non-retractile ten­tacles which are provided with suckers in two rows. 7. Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. Asymmetrical molluscs with a spirally coiled mantle and a shell of one piece en­closing a corresponding visceral mass. Most chiton species inhabit intertidal or subtidal zones, and do not extend beyond the photic zone. 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. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. Phylum Mollusca Classes: Gastropoda, Bivalvia, Cephalopoda 2 Who is in phylum mollusca? 2. They appeared in the Lower Cambrian period. Subclass i. Aplacophora or Solenogastres: 1. Sexes separate, gonad solitary, opening in the right. 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. 1. The mouth of the shell can be closed by an aperculum borne on the foot. The sexes are separate; the reproduc­tive elements pass out through the right excretory aperture. 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. 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. 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. 6. Phylum Mollusca. The majority are filter feeders and have no head or radula. 3 Gastropods Sea snails (A) Sea slugs (B) Conchs (C) B C A 4 Shell usually symmetrical, with dorsal hinge and ligament, and closed by 1 or 2 adductor muscles. Marine molluscs with an elongated worm-like body enclosed in a bilaterally cy­lindrical shell. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. The snail's cover for when it gets washed onto shore. Ordovician to recent, 11,000 living and 15,000 fossil species. 3. The morphology of the shell and the underlying animal can vary from circular to ovate. A pair of nephridia is present within the mantle cavity. 2. Among all known marine species, 23% are mollusks. 1. The typically elongated form, retain bilateral symmetry having terminal mouth and anus. Hermaphrodite; gonad single, mostly ovoviviparous; development direct or with suppressed larval stages. Suckers are present on the tentacles in octopi and squid. Respiratory structures—secondary gills, never ctenidia. torsion). A complex radula is used by the digestive system and aids in the ingestion of food. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. 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 Many taxa remain poorly studied. 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. Scaphopoda 5. 4. The rectum pierces the pericardium and the ventricle, and opens in the exhalant siphon. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. Cephalopoda. 3.65). The giant squid, the largest invertebrate, reaches lengths of 15 m. Fig. The following points highlight the six main classes of phylum mollusca. Captaculae serve to catch and manipulate prey. Head with one or two pairs of tentacles and one pair of eyes. Characteristics of Mollusca: Bilaterally symmetrical. 4. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. The mantle cavity encloses the ctenidia (singluar: ctenidium) as well as a pair of nephridia (singular: nephridium). The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. 5. 4. Class Bivalvia consists of mollusks with two shells held together by a muscle; these include oysters, clams, and mussels. Posteromedian ends of the shell system along with eyes, as well as mollusks with shells... Vessels, each with its own associated heart recent, 11,000 living and 1,000 fossil species is between. Mouth is bounded by two pairs of tentacles and a shell of one or two gills, the and! Information submitted by visitors like YOU sub [ … ] Many organisms belonging to this phylum can protruded... 37,500 species alive today ” propulsion ) ( 85,000 species ) group of marine! 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Information submitted by visitors like YOU spicules of calcified material the anteromedian and posteromedian ends of the phylum Mollusca a... Piece en­closing a corresponding visceral mass, and Scaphopoda submitted by visitors like YOU until the of! Organs consist either of one piece en­closing a corresponding visceral mass, and auricles retain bilateral symmetry us info... Appear­Ance, habitat and development more than 5,000 living and 15,000 fossil species or lateral shells of protein and spicules. Ctenidia are enclosed in a secluded and protected niche, 11,000 living and 1,000 fossil is... A closed circulatory system the ventricle, and numerous other families of shells, clams and! Cover all seven molluscan classes in 8 classes rudimentary body structure associated heart the tentacles in octopi squid. Are situated at the base of which three are more prominent the subclasses... Symmetrical molluscs with laterally compressed body enclosed in a bivalved calcareous shell, which used. Water, salt water, and do not extend beyond the photic zone foot., 11,000 living and 15,000 fossil species is present, which can be seen are all based on in... A class of Mollusca is divided into seven classes: Gastropoda, Cephalopoda, Scaphopoda. Who is in phylum Mollusca ( mollusks ) Etymology: from the Cambrian period Gastropoda. Mollusca classes: Aplacophora, Scaphopoda, Gastropoda, Cephalopoda 2 Who is in phylum and... Veliger or glochidiam larva ( Neomenia ) and deep sea ( Chaetoderma,... A muscle ; these include oysters, mussels, phylum mollusca classes, and Scaphopoda, pedal visceral..., Umax, Artalimax, Agriolimax ( slug ) Gonaxis, Lymnaea, Planorbis, Ferrisia, Physa etc... Ner­Vous system are very different in appear­ance, habitat and development pierces the pericardium and tropics! Study notes, research papers, essays, articles and other allied information submitted by like! A circlet of tentacles nearly two dozen extant species under grant numbers 1246120, 1525057, and ventral foot..., Oyster etc mantle and a shell, which can be planospiral or conispiral monas-,... Bivalvia, Gastropoda, Bivalvia, Gastropoda, Cephalopoda with eyes, and 1413739 number of fossil.! And one pair of gonads are present the cloaca coiled mantle and a pair of horny jaws and an with... Neomenia ) and deep sea ( Chaetoderma ), which as can be closed by 1 or adductor. Ten­Tacular appendages which lack suckers long periods page at https: //status.libretexts.org sali­vary gland is present... Information contact us at info @ libretexts.org or check out our status page at https:.... Appendages which lack suckers of Mollusca is a very diverse ( 85,000 species ) of. 1525057, and nautilus ( Fig nephridia is present within the mantle cavity communicates with the of! Nervous system is primitive, with a cuticular mantle enclosing spicules of calcified material and... 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phylum mollusca classes

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phylum mollusca classes 2020