2. Class Aplacophora (“bearing no plates”) includes worm-like animals primarily found in benthic marine habitats. The nervous system consists of cerebral, pleural, buccal, pedal, visceral and abdominal ganglia with their connectives and commissures. The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. monas- one, plax- plate, pherein- bearing): The shell is spoon or cup shaped. Missed the LibreFest? The morphology of the shell and the underlying animal can vary from circular to ovate. The shell may be absent or rudimentary; when present may be internal or external, undivided or divided internally into a series of chambers. 9. 3. The two subclasses of the class Amphineura sharing a similar primitive nervous system are very different in appearance, habitat and development. Marine molluscs with an elongated worm-like body enclosed in a bilaterally cylindrical shell. "stomach-footed animal". Animals in the class Polyplacophora (“bearing many plates”) are commonly known as “chitons” and bear an armor-like, eight-plated dorsal shell. The rest of the foot forms a siphon on the ventral surface of the body. This is a product of Mexus Education Pvt. 5. 5. But the giant octopus (Enteroctopussp. 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 . 249-320. TOS4. 6. 2. Privacy Policy3. The phylum Mollusca is divided into the following seven classes: Monoplacophora, Polyplacophora, Aplacophora, Scaphopoda, Gastropoda, Bivalvia, Cephalopoda. 5. The head bears eight non-retractile tentacles which are provided with suckers in two rows. The body is bilaterally symmetrical and covered by a mantle. 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. Shell external, many-chambered, siphunculate and coiled or straight. One pair of ctenidia, osphradia, auricles and renal organs present. Examples: Loligo, Sepia, Octopus, Argonauta, etc.. The nervous system is ladder-like, with slightly developed ganglia. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. 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. Members of a species mate, then the female lays the eggs in a secluded and protected niche. Their body has a cavity. The cephalopods are molluscs with large heads and tentacles. The foot is behind the head and is typically a flat, creeping organ. Monoplacophora: 1. A pair of nephridia is present within the mantle cavity. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 11. Mollusca makes the second largest phylum of non-chordate animals including snails, octopuses, sea slugs, squid, and bivalves such as clams, oysters, and mussels. Upper Cambrian to recent; more than 5,000 living and 1,000 fossil species. 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. Occur most commonly in the littoral and sub-littoral rocky shores. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. The mollusca phylum is split up into eight classes of mollusks, the three major ones being Gastropoda, Bivalvia, and Cephalopoda. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. amphi- both + two neuron = nerve): 2018. […] Have questions or comments? The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. 5. 7. 2. Class Bivalvia consists of mollusks with two shells held together by a muscle; these include oysters, clams, and mussels. 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 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. The sexes are either separate or united. Most chiton species inhabit intertidal or subtidal zones, and do not extend beyond the photic zone. 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