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. (examples: snails, conch, slugs, nudibrancs) All Univalve (one-shelled or no shell) Operculum. 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. Asymmetrical molluscs with a spirally coiled mantle and a shell of one piece enclosing a corresponding visceral mass. Before publishing your Notes on this site, please read the following pages: 1. 4. The mouth and anus are situated at the anteromedian and posteromedian ends of the foot. 5. 1. Class Cephalopoda (“head foot” animals) includes octopi, squids, cuttlefish, and nautilus. Two pairs of ctenidia, osphradia, renal organs, and auricles. Their body has a cavity. Bilaterally symmetrical, free-swimming, marine molluscs. 2. 3.65). The mouth opens at the end of a short buccal tube, at the base of which is a circlet of tentacles. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. All cephalopods show the presence of a very well-developed nervous system along with eyes, as well as a closed circulatory system. The proportion of undescribed species is very high. Calcareous spines may be present on the girdle to offer protection from predators. The gills one or two pairs (ctenidia or branchia), commonly plate-like. Phylum Mollusca is the second largest animal phylum. Sexual dimorphism is seen in this class of animals. Respiratory organ a lung, fused with the mantle in the adult. […] The phylum Mollusca is commonly divided into seven classes: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Monoplacophora, Polyplacophora and Aplacophora. But some species live in freshwater and terrestrial habitats. 6. The mantle cavity encloses the ctenidia (singluar: ctenidium) as well as a pair of nephridia (singular: nephridium). The mouth lies centrally in a reduced head, the anal and excretory apertures are posterior. Examples: Loligo, Sepia, Octopus, Argonauta, etc.. The members are known as molluscs or mollusks . Marine molluscs with an elongated, bilaterally symmetrical flattened body and a broad foot ventrally. 5. The sexes are either separate or united. 1. 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. 10. Marine gastropods displaying reduction or loss of shell (shell sometimes internal). Hermaphrodite; larva is a veliger, Carboniferous to recent; 3,000 living and 300 fossil species. 8. A flat creeping ventral foot is present. Digestive glands are not distinct; salivary gland is usually present. The number of fossil species is estimated between 60,000 and 100,000 additional species. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The body is bilaterally symmetrical and covered by a mantle. Phylum Mollusca, contains 75-80% of all animals in Phylum. 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 . Welcome to NotesOnZoology.com! 2. 4. Cephalopoda. 7. 7. The asymmetry of visceropallium is its fundamental feature. Weird Science: An Inordinate Fondness for Beetles; Activity: Aquatic Invertebrate Behavior; Question Set: Phylum Arthropoda; Further Investigations: Phylum Arthropoda; Phylum Echinodermata. 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. The snail's cover for when it gets washed onto shore. 5. Most gastropods bear a head with tentacles, eyes, and a style. Neometiia is hermaphroditic whereas Chaetoderma is dioecious. torsion). Classes and General characteristics of Vertebrates. The foot is lobed and developed into tentacles and a funnel, which is used as the mode of locomotion. Amphineura (Gk. Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. 8. 3. Animals in the class Polyplacophora (“bearing many plates”) are commonly known as “chitons” and bear an armor-like, eight-plated dorsal shell. 7. They exhibit organ system level of organization. Example: Neopilina. The nervous system consists of paired cerebral, pedal and visceral ganglia with their connectives. Class # 1. Examples: Aplysia (sea hare), Actean, Gastropteron (sea slug), Cliona, Bertholimia, Polycera, Doris, Dendonotus, etc. Examples: Lamellidens, Unio, Anodonta, Mytilus, Teredo, Oyster etc. No distinct head; Examples: Mussels, Unio, Mytilus, Gastropoda includes shell-bearing species as well as species with a reduced shell. A well-developed head bearing eyes and tentacles are usually present. 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. Phylum Mollusca… Phylum Mollusca Classification Mollusca (mollusks) are classified into 6 classes according to their symmetry and the characters of food, shell, mantle, … Gastropoda This class of mollusca is the largest out of the major classes with over 37,500 species alive today. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. Marine, found in shallow (Neomenia) and deep sea (Chaetoderma), feeding upon hydroids, corals, etc. Head with one or two pairs of tentacles and one pair of eyes. 1. Body possesses a through gut with mouth and anus. 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. Phylum Mollusca. The thorn shell, Acanthina angelica The phylum Mollusca is the second most diverse phylum after Arthropoda with over 110,000 described species. 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. [ "article:topic", "authorname:boundless", "showtoc:no" ], Differentiate among the classes in the phylum mollusca. 3. Body cylindrical or globose, often with fins. The cephalopods are molluscs with large heads and tentacles. Chitons live worldwide, in cold water, warm water, and the tropics. Primarily aquatic gastropods, retaining larval torsion and nervous asymmetry. The odontophore is with a simple radula. 3. The rectum pierces the pericardium and the ventricle, and opens in the exhalant siphon. Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Phylum : Mollusca . 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 body is elongated and worm-like and enveloped by the mantle. 249-320. Ctenidia are absent in these animals. 2. 4. Phylum Mollusca (Mollusks) Etymology: From the Latin Molluscus, meaning soft of body. The following points highlight the six main classes of phylum mollusca. 4. 8. 5. 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. Larval stages are trochophore and veliger. Classification of Phylum Mollusca: Phylum Mollusca are divided into six classes. 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. Amphineura 3. A ventral longitudinal groove is present, which is connected anteriorly with a ciliated groove and posteriorly with the cavity of the cloaca. A looped digestive system, multiple pairs of excretory organs, many gills, and a pair of gonads are present in these animals. The mantle has siphonophores that facilitate exchange of water. 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 This is a product of Mexus Education Pvt. They are mostly found in marine and fresh water. 5. 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. 8. amphi- both + two neuron = nerve): Gastropoda 4. Eyes are open vesicles without cornea or lens. Members of class Monoplacophora have a single shell that encloses the body. The head bears eight non-retractile tentacles which are provided with suckers in two rows. 2. The typically elongated form, retain bilateral symmetry having terminal mouth and anus.