phylum mollusca classes

Bivalves include clams, oysters, mussels, scallops, and numerous other families of shells. Largest is Gastropoda. 5. The mantle bearing cuticular spicules covers at least a great part of the body. They exhibit organ system level of organization. The sexes are either separate or united. Class # 1. The head comprises of tentacles and compound eyes. 8. Scaphopoda 5. Pelecypoda or Bivalvia or Lamellibranchiata 6. They are bilaterally symmetrical, triploblastic and coelomate animal. This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. Marine molluscs with an elongated worm-like body enclosed in a bilaterally cy­lindrical shell. 249-320. 3. Phylum Mollusca is the predominant phylum in marine environments. Example: Nautilus pompilius. Pelecypoda or Bivalvia or Lamellibranchiata 6. The monoplacophorans were believed extinct and only known via fossil records until the discovery of Neopilina galathaea in 1952. Calcareous spines may be present on the girdle to offer protection from predators. Bilaterally symmetrical, free-swimming, marine molluscs. 5. The classes are: 1. They have die characters of both the phylum Annelida and phylum Mollusca. Locomotion in cephalopods is facilitated by ejecting a stream of water for propulsion (“jet” propulsion). Hermaphrodite; gonad single, mostly ovoviviparous; development direct or with suppressed larval stages. 3.65. 3. The typically elongated form, retain bilateral symmetry having terminal mouth and anus. 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. Head is not distinct and without eyes and tentacles. Respiratory structures—secondary gills, never ctenidia. The Phylum Mollusca is familiar to us as invertebrate animals, as it includes snails, clams, squid, oysters, sea-mice and tusk shells. 2. The body is divided into segments. Content Guidelines 2. Cephalopoda. PHYLUM: MOLLUSCA Authors Dai Herbert1, Georgina Jones2 and Lara Atkinson3 Citation Herbert DG, Jones GJ and Atkinson LJ. 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 . They appeared in the Lower Cambrian period. These animals lack a calcareous shell, but possess aragonite spicules on their epidermis. 1. Comprehensive genomics resources offered by MolluscDB cover all seven molluscan classes. The foot is behind the head and is typically a flat, creeping organ. Phylum : Mollusca . 2. Body has more than two cell layers, tissues and organs. Sexual dimorphism is seen in this class of animals. A flat creeping ventral foot is present. A free-swimming trochophore larva is succeeded by a veliger. Upper Cambrian to recent; 25,000 living and 10,000 fossil species. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. Their key characteristic is the torsion around the perpendicular axis on the center of the foot that is modified for crawling. 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. 2. Scaphopods are usually buried in sand with the anterior opening exposed to water. Animals, Biology, Diversity, Phylum Mollusca, Zoology. 5. Phylum Mollusca is the second largest animal phylum. 2. In majority, there is an ink gland open­ing in the rectum. 4. The mollusca phylum is split up into eight classes of mollusks, the three major ones being Gastropoda, Bivalvia, and Cephalopoda. Gastropoda includes shell-bearing species as well as species with a reduced shell. 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 Gastropods Sea snails (A) Sea slugs (B) Conchs (C) B C A 4 The nervous system is ladder-like, with slightly developed ganglia. They live in fresh water, salt water, and on land. These animals are asymmetrical and usually present a coiled shell. A complex radula is used by the digestive system and aids in the ingestion of food. Some species live quite high in the intertidal zone and are exposed to the air and light for long periods. The foot is lobed and developed into tentacles and a funnel, which is used as the mode of locomotion. Phylum Mollusca… 8. Scaphopoda 5. 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. One pair of ctenidia, osphradia, au­ricles and renal organs present. Larval stages are trochophore and ve­liger. The Phylum Mollusca is considered one of the largest phyla in the animal kingdom.There are at least 100,000 known species. Classification of Phylum Mollusca. The head is surrounded by a series of arms bearing suckers, which are modified part of the foot. 11. The shell is a curved tube open at both the ends, the opening being wider at the oral and narrower at the other end. Cephalopoda. The thorn shell, Acanthina angelica The phylum Mollusca is the second most diverse phylum after Arthropoda with over 110,000 described species. The buccal cavity contains an odontophore with a radula bearing rows of chitinoid teeth. 10. 9. 1. The cephalopods are molluscs with large heads and tentacles. The larva passes through trochophore and veliger stages. Ctenidia are absent in these animals. monas- one, plax- plate, pherein- bearing): The shell is spoon or cup shaped. The bodies are generally very soft and are covered by the hard exoskeleton. 9. Monoplacophora 2. Phylum Mollusca Classes: Gastropoda, Bivalvia, Cephalopoda 2 Who is in phylum mollusca? 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 These animals bear a single conical shell, which has both ends open. 10. The classes are: 1. […] Limpets. All cephalopods show the presence of a very well-developed nervous system along with eyes, as well as a closed circulatory system. The odontophore is with a simple radula. 4. ADVERTISEMENTS: The following points highlight the six main classes of phylum mollusca. TOS4. Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 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. Members of a species mate, then the female lays the eggs in a secluded and protected niche. Phylum Mollusca. This video explains the characteristics and Classes of the Phylum Mollusca. Most cephalopods are relatively small. 5. 6. The mouth lies centrally in a reduced head, the anal and excretory apertures are posterior. 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. Very few are terrestrial found in damp soil. The shell consists of eight separate pieces on dorsal surface and studded later­ally with scales or spines to form a girdle. The sexes are separate and develop­ment is direct. Most gastropods bear a head with tentacles, eyes, and a style. The heart consists of two auricles and a ventricle. 3. torsion). 5. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. 5. Before publishing your Notes on this site, please read the following pages: 1. 6. The proportion of undescribed species is very high. 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. 1. 4. Sexes separate, gonad solitary, opening in the right. Amphineura 3. 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. The first two classes are thought to represent primitive molluscs, the last three classes include the great bulk of living species. Digestive glands are not distinct; sali­vary gland is usually present. 7. Chitons live worldwide, in cold water, warm water, and the tropics. Gastropoda This class of mollusca is the largest out of the major classes with over 37,500 species alive today. Examples: Haliotis, Pila, Viviparus, Pa­tella, Acmaea, Fissurella, Cypraea, Littorina, Murex, Buccinum, Conus, etc. Neometiia is hermaphroditic whereas Chaetoderma is dioecious. Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. 2. 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. 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. This phylum contains about 100,000 described species. This group displays a broad range of morphological […] Animals in class Gastropoda (“stomach foot”) include well-known mollusks like snails, slugs, conchs, sea hares, and sea butterflies. 5. 4. Monoplacophora: 1. 249 2. 4. 2. Classes and General characteristics of Vertebrates. The two subclasses of the class Amphineura sharing a similar primitive ner­vous system are very different in appear­ance, habitat and development. (B) The co… Today, scientists have identified nearly two dozen extant species. 4. It is a small class of marine molluscs dating back from the Cambrian period. 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. Class Bivalvia consists of mollusks with two shells held together by a muscle; these include oysters, clams, and mussels. 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 … Their body has a cavity. The single dorsal shell is thin and sub circular. 6. 2. Class Cephalopoda (“head foot” animals) includes octopi, squids, cuttlefish, and nautilus. They are mostly found in marine and fresh water. Females of some species care for the eggs for an extended period of time and may end up dying during that time period. They can be found in terrestrial regions as well as in the depths of the seas. 1. 1. Mantle cavity communicates with the exterior through an oval, closeable pneumostome. 3. The number of fossil species is estimated between 60,000 and 100,000 additional species. Body possesses a through gut with mouth and anus. Two pairs of ctenidia, osphradia, renal organs, and auricles. 3. Monoplacophora (Gk. 6. The gills one or two pairs (ctenidia or branchia), commonly plate-like. Class 1 Pelecypoda or Bivalvia. 1. The mantle cavity acting as the respiratory chamber. 3. Marine gastropods displaying reduc­tion or loss of shell (shell sometimes inter­nal). Untwisting and shortening of visceral loop and pleuroparietal nerve connectives due to de-torsion is pronounced. The sexes are separate; the reproduc­tive elements pass out through the right excretory aperture. The body is covered by a shell made up of calcium carbonate. Examples: Loligo, Sepia, Octopus, Argonauta, etc.. (A) Caribbean reef squid (Sepioteuthis sepioidea) Image courtesy of Betty Willis, Wikimedia Commons Fig. 6. "stomach-footed animal". 4. 8. A ventral longitudinal groove is present, which is connected anteriorly with a ciliated groove and posteriorly with the cavity of the cloaca. The mouth opens at the end of a short buccal tube, at the base of which is a circlet of tentacles. Head with one or two pairs of tentacles and one pair of eyes. 5. Missed the LibreFest? 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 can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Gastropoda 4. Subclass i. Aplacophora or Solenogastres: 1. Siphonal funnel of two separate folds. The mouth of the shell can be closed by an aperculum borne on the foot. 1. 2018. Cephalopods are a class of shell-bearing animals as well as mollusks with a reduced shell. 3.65). 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 is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. The shell of a bivalve is composed of calcium carbonate, and consists of two, usually similar, parts called valves. The phylum Mollusca is commonly divided into seven classes: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Monoplacophora, Polyplacophora and Aplacophora. The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. Occur most commonly in the littoral and sub-littoral rocky shores. Classes in Phylum Mollusca Phylum Mollusca is a very diverse (85,000 species ) group of mostly marine species, with a dramatic variety of form. Examples of cephalopod molluscs include squid, octopus, cuttlefish, and nautilus (Fig. 6. 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. 7. 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 respiratory organs consist either of one or two gills, or a gill and a pulmonary sac or a lung. Sexes are separate or united; develop­ment with a veliger or glochidiam larva. They display vivid coloration, typically seen in squids and octopi, which is used for camouflage. Ctenidia are enclosed in a large mantle cavity serviced by blood vessels, each with its own associated heart. Asymmetrical molluscs with a spirally coiled mantle and a shell of one piece en­closing a corresponding visceral mass. Many organisms belonging to this phylum have a calciferous shell. 3. Monoplacophora 2. Ordovician to recent, 11,000 living and 15,000 fossil species. 9. The body is bilaterally symmetrical and covered by a mantle. Bivalvia is a class of marine and freshwater molluscs with laterally compressed bodies enclosed by a shell in two hinged parts. The asymmetry of visceropallium is its funda­mental feature. Devonian to recent; 300 fossil and 100 living species. 4. Many taxa remain poorly studied. 4. But some species live in freshwater and terrestrial habitats. The rest of the foot forms a siphon on the ventral surface of the body. 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. 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. 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. Head with numerous retractile ten­tacular appendages which lack suckers. These animals continue to have an important role in the lives … 7. Privacy Policy3. 1. The mantle encloses a large mantle cavity in which are situated the gills, the renal, reproductive and the anal apertures. The following diagram shows the major classes, which as can be seen are all based on variation in this same body plan. Characteristics of Mollusca: Bilaterally symmetrical. The nervous system consists of paired cerebral, pedal and visceral ganglia with their connectives. The mouth and anus are situated at the anteromedian and posteromedian ends of the foot. 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. 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. Example: Neopilina. The rectum pierces the pericardium and the ventricle, and opens in the exhalant siphon. Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks . Eyes are open vesicles without cornea or lens. Examples: Neometiia, Proneomenia, Chaetoderma, etc. Marine, found in shallow (Neomenia) and deep sea (Chaetoderma), feeding upon hydroids, corals, etc. 4. Shell single piece with a simple spiral or none. But the giant octopus (Enteroctopussp. Phylum Mollusca and Phylum Echinodermata belong to the Kingdom Animalia. The v… 7. Visceral complex usually incorporated into head-foot complex, leading to second­ary external bilateral symmetry. 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. Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and calcareous spicules. There are six classes of which three are more prominent. 1. The head is rudimentary and protrudes out of the posterior end of the shell. Phylum Mollusca is the Large phylum of invertebrates having 100,000 species distributed in 8 classes. The shell may be absent or rudimen­tary; when present may be internal or exter­nal, undivided or divided internally into a series of chambers. 4. The phylum Mollusca includes a wide variety of animals including the gastropods (“stomach foot”), the cephalopods (“head foot”), and the scaphopods (“boat foot”). (examples: snails, conch, slugs, nudibrancs) All Univalve (one-shelled or no shell) Operculum. 2. Body is covered by a calcareous shell and is unsegmented with a distinct head, muscular foot and visceral hump. 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. 6. 3. 2. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. 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. Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Examples Achatina, Helix, Umax, Artalimax, Agriolimax (slug) Gonaxis, Lymnaea, Planorbis, Ferrisia,Physa, etc. This is a product of Mexus Education Pvt. The metamerism is apparent and not represented externally. 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. Phylum Mollusca, contains 75-80% of all animals in Phylum. 4. Among all known marine species, 23% are mollusks. Bilaterally symmetrical molluscs with a laterally compressed body enclosed in a bivalved calcareous shell. Question Set: Phylum Mollusca; Further Investigations: Phylum Mollusca; Phylum Arthropoda. 2. The majority are filter feeders and have no head or radula. 1. The body is bilaterally symmetrical and covered by a mantle. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species. Upper Cambrian to recent; more than 5,000 living and 1,000 fossil species. 5. The mouth is bounded by two pairs of labial palps acting as lips. Class 2. amphi- both + two neuron = nerve): A pair of horny jaws and an odontophore with a radula are present. Around 85,000 extant species of molluscs are recognized. Suckers are present on the tentacles in octopi and squid. 8. All animals in this class are carnivorous predators and have beak-like jaws at the anterior end. The giant squid, the largest invertebrate, reaches lengths of 15 m. Fig. The nervous system consists of cere­bral, pleural, buccal, pedal, visceral and ab­dominal ganglia with their connectives and commissures. 6. 7. Captaculae serve to catch and manipulate prey. Animals in the class Polyplacophora (“bearing many plates”) are commonly known as “chitons” and bear an armor-like, eight-plated dorsal shell. The head bears a pair of large, simple eyes. Shell usually symmetrical, with dorsal hinge and ligament, and closed by 1 or 2 adductor muscles. Phylum Mollusca. 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. The organisms belonging to phylum Mollusca exhibit the following characteristics: 1. 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.. A pair of nephridia is present within the mantle cavity. Hermaphrodite; larva is a veliger, Car­boniferous to recent; 3,000 living and 300 fossil species. Respiratory organ a lung, fused with the mantle in the adult. Amphineura (Gk. Phylum Mollusca (Mollusks) Etymology: From the Latin Molluscus, meaning soft of body. The nervous system is primitive, with longitudinal pallial and pedal cords with cross anastomoses. Weird Science: An Inordinate Fondness for Beetles; Activity: Aquatic Invertebrate Behavior; Question Set: Phylum Arthropoda; Further Investigations: Phylum Arthropoda; Phylum Echinodermata. Mantle cavity opens anteriorly and con­tains two ctenidia anterior to heart. A well-developed head bearing eyes and tentacles are usually present. 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. The body is elongated and worm-like and enveloped by the mantle. These classes are distinguished by, among other criteria, the presence and types of shells they possess. The phylum Mollusca is divided into the following seven classes: Monoplacophora, Polyplacophora, Aplacophora, Scaphopoda, Gastropoda, Bivalvia, Cephalopoda. 1. Welcome to NotesOnZoology.com! 1. Eyes may be absent in some gastropods species. Examples: Aplysia (sea hare), Actean, Gastropteron (sea slug), Cliona, Bertholimia, Polycera, Doris, Dendonotus, etc. Body without cavity. Habitat: mostly marine; They burrow in mud and sand. Watch the recordings here on Youtube! The morphology of the shell and the underlying animal can vary from circular to ovate.

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