The largest living bivalve species is giant clam (Tridacna gigas) which can grow up to 47 inches (1,200 mm) in length and more than 200 kg in weight. Examples: Mya arenaria (soft-shell clam),  Mercenaria mercenaria (hard clam). In aquatic mollusks, respiration occurs through gills or ctenidia which are located in the mantle cavity while in terrestrial forms, it occurs through lungs (pulmonary sacs) or general body surface. In this case, the shell is a hard calcareous structure, made up of calcium carbonate. Study of Mollusca is called Malacology. Sense organs are eyes, tentacles, osphradium and statocyst. Mollusca is the second largest phylum which contains over 75,000 described species. https://www.toppr.com/guides/biology/animal-kingdom/phylum-mollusca Mix Play all Mix - Magnet ... Phylum Characteristics … Sexes are usually separate but some are monoecious. This phylum can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. They are a small group of mollusks which contains about 320 species. They have a bilaterally symmetrical body with a spiral or coiled shell. Body possesses a through gut with mouth and anus. Most molluscs are marine, some freshwater, some terrestrial. Among 65,000 species, about 30,000 are marine, 5,000 inhabit in freshwater, and 30,000 live on land. Circulatory system is closed or open type. 2. It overlaps the … This phylum has 50,000 living species. Widely distributed over the world. They are mostly marine, few fresh water and also found in damp soil. General Characteristics of Phylum Mollusca They have a bilaterally symmetrical body (exception: gastropods body asymmetrical) and show organ system grade of organization. Lamarck coined the term Molluscus. They include slow-moving snails and slugs bivalved (shell with two parts) clams and highly active cephalopods. amzn_assoc_title = "Shop Your Products"; Body without cavity. They have a bilaterally symmetrical body with a curved anterior apex, and a ventral foot and mouth. Their brain is large and well-developed in contrast to any other mollusks. amzn_assoc_default_search_phrase = "Tablets"; The phylum Mollusca is an extremely vast group of animals with a resultantly vast array of physical attributes, although some features are shared by all creatures who are a part of it. Required fields are marked *. amzn_assoc_search_bar = "true"; They are characterized by a shell which is divided into left and right valves. The foot is reduced and modified into tentacles. They are also known as tusk shells, elephant’s tusk, elephant’s tooth or tooth shells. Generally, their foods consist of small organisms such as foraminiferans and young bivalves. They are mostly aquatic organisms. Schizocoel or Haemocoel cavity found as coelom. Examples: Octopus abaculus, Loligo vulgaris, Sepia dubia. Among all known marine species, 23% are mollusks. But some species live in freshwater and terrestrial habitats. The v… Excretion takes place by paired metanephridia (kidney). Their body has a cavity. The vast Phylum Mollusca contians a great diversity of speciation and, with that, many different and unique characteristics. The most commonly shared features are often internal. 4 amzn_assoc_marketplace = "amazon"; This group displays a broad range of morphological features such as a muscular foot, a mantle and visceral mass containing internal organs. What is an identifying characteristic of cephalopods? But all Molluscs have the same basic structure. Molluscs are present in most Nearctic freshwater habitats other than hypersaline lakes, which are colonized by only a few snail species (Assiminea spp. The classes are: 1. 3.51 A). Molluscs show a great variety of form (structure). 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. They have multiple pairs of excretory organs (nephridia) which are arranged serially. They live their adult lives buried in sand or mud. Nervous system consists of many paired ganglia, connectives and nerves. Fig. The shell is either external, internal or absent. Body Characters:They are triploblastic, coelomate and show bila… Class # 1. They do not have a head with no eyes or eyespots. The body is divided into head, dorsal visceral mass, and ventral muscular foot and mantle. They play an important role in the lives of humans because they are the source of food for many people as well as jewellery. A simple velum is present which surrounds the mouth and the head does not bear tentacles or eyes. Habitat: They are mostly marine. Many molluscans are not good for human’s lives. Body has more than two cell layers, tissues and organs. g. Mollusca. They have a modified foot. There is a between Mollusca and Echinodermata in terms of morphological, physiological and behavioural characteristics. They show direct or indirect development with trochophore or veliger larval stages. Respiration takes place through one or more gills or ctenidia, lungs (pulmonary sac) or general body surface in the terrestrial forms. amzn_assoc_default_browse_node = "672123011"; amzn_assoc_placement = "adunit0"; Sense organs consist of eyes, osphradium, tentacles, and. For example, all mollusks have a mantle. Glory-of-the-sea snail (Conus gloriamaris) is prized by collectors for its ornate shell. 2)Body has more than two cell … General Characteristics of Phylum Mollusca (Mollis or molluscs: soft) Kingdom: Animalia; Habitat: Mostly aquatic and few are terrestrial; Body is soft without segmentation; Grade of organization: Organ system grade; Germ layer: Triploblastic; Symmetry: BIlaterally symmetry; The body is divided into head, muscular foot and visceral mass. They are triploblastic animals with un-segmented (exception: Mantle and shell cover the body and the body has three regions namely: head, ventral foot, and a visceral mass. Most of the animals of this class inhabit rocky intertidal or shallow subtidal zones but few live in more than 7000 meters depth. Class Bivalviaconsists of molluscs that have two connected shells such as Oysters, Clams, Mussels, Scallops and many more. Head consists tentacles and compound eyes. Hippurate Hydrolysis Test- Principle, Uses, Procedure, Result Interpretation with Limitations, HAEMAGGLUTINATION ASSAY – VIRAL QUANTITATION. Body is unsegmented (except Neoplina) and bilaterally symmetrical (except few twisting forms like Pila). The following are present in all modern molluscs: The dorsal part of the body wall is a mantle (or pallium) which secretes calcareous spicules, plates or shells. amzn_assoc_marketplace = "amazon"; It is a cephalopod having, Blood consists of copper containing pigment called haemocyanin. In this article we will discuss about the general characters and classification of Phylum Mollusca. Select one: a. Nematoda. The term Mollusca was first applied by Aristotle to cuttle fish. External or internal fertilization occurs. The single dorsal shell is thin and sub […] amzn_assoc_default_category = "PCHardware"; Pelecypoda or Bivalvia or Lamellibranchiata 6. The nervous system is simple that contains two pairs of lateral nerve cords with several special tiny sensory organs. Osphradia- chemoreceptor to test chemical nature of the water. Amphineura 3. Examples: Cadulus delicatulus, Dentalium americanum. Very few are terrestrial found in damp soil. in Biology The tentacles have a bulbous end which is known as captaculae. They have no eyes, tentacles, and nephridia but radula is present. 8. Save my name, email, and website in this browser for the next time I comment. Phylum Mollusca can be divided into the following different classes: This class comprises more than 15000 species including mussels, oysters, clams, scallops, etc. Fertilization is external (in sessile group such as in oyster) or internal. They have a “pen.” c. Annelida. This makes finding universal traits an extraordinarily difficult task. 3. amzn_assoc_default_browse_node = "13900871"; amzn_assoc_placement = "adunit0"; Phylum Mollusca is a very diverse (85,000 species) group of mostly marine species, with a dramatic variety of form. amzn_assoc_linkid = "df6e3e2dfb2223ece0caaeddeb1e4806"; The … Phylum Mollusca (Mollusks) Lophotrochozoa The Mollusca Sea slugs, squid, snails, and scallops . In this case, sexual reproduction occurs. The body contains eight overlapping dorsal plates. The class Gastropoda contains more than 65,000 species which make the largest group in the phylum Mollusca comprising over 80% of all mollusks. Mostly aquatic (marine and few are fresh-water) and some are terrestrial living in damp soil. Examples: Turritella cumberlandia, Diastoma insulaemaris, Epitonium charlestonensis, Pila globosa (Apple snail). Animal kingdom: Phylum Mollusca in detail - Duration: 10:09. 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