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Study of Molluscs

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Coastal and marine ecosystem
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Study of Molluscs

  1. 1. Conus: • It is a highly carnivorous gastropods. • Generally found below the low water and considered as pests on the oyster beds. • It injects poison into the body of the prey and cause paralysis. • Tongue is modified and bear and bear 3 -4 whorls, last one being largest. • A pair of tentacles and eyes are present. • Foot is long, sole like with which animal efficiently attached on the rocky shore.
  2. 2. Phyllum: Mollusc Class : Gastropod Family: Conidae Genus: Conus
  3. 3. Cypraea • It is commonly known as ‘Cowry’. • It is marine and found in rocky shores and coral reefs. • The shell is convolute, oval above and flattened below. • Surface of the shell is smooth, polished and brightly colored. • shell opening is long, narrow. • In the young stages, the shell has a prominent spire and long siphon.
  4. 4. Phyllum: Mollusc Class : Gastropod Family: Cypraeidae Genus: Cypraea
  5. 5. Perna • It is commonly known as Green mussel. • Marine in their habitat, found more extensively in rocky shore areas. • Body enclosed in a wedge shaped shell with two equal halves. It is pointed in front and rounded behind. • Byssal thread protrudes between two shell valves, virtually by which it is attached to stones and rocks.
  6. 6. • Foot is cylindrical, elongated with a ventral groove, continuous with byssus pit. • Pair of gills present. • Sexes are separate. Gonads extend into the mentle. • Extensively used as test animal in pollution related works.
  7. 7. Phyllum: Mollusc Class : Bivalvia Family: Mytilidae Genus: Perna
  8. 8. General Characteristics: • Mollusc are mostly marine. Many occur in fresh water and some are terrestrial forms. • Body of molluscs is un-segmented and bilaterally symmetrical with a distinct head, muscular foot and visceral mass. • Body is commonly protected by an exoskeleton calcareous shell of one or more pieces which is secreted by mentle. • Mentle (pallium) is a thin, fleshy fold of dorsal body wall more or less covering the body. It encloses a space, which is called mantle cavity
  9. 9. Classification of Phyllum Mollusc 7 Classes: 1. Aplacophora 2. Polyplacophora 3. Monoplacophora 4. Gastropoda 5. Scaphopoda 6. Pelecypoda 7. Cephalopoda
  10. 10. Chiton: • Chiton are commonly known as ‘sea cradles’ • They are marine molluscs of varying size found attached to the rocks, empty shells and corals between the tide marks. • Body is elongated, bilaterally symmetrical and dorsoventrally compressed consists of shell, foot, mantle and visceral mass. • The shell is calcareous, present on the dorsal side and composed of eight overlapping plates. Head is not distinct, eyes and tentacles are present. • Foot is ventral muscular with a flat side extending along the whole length of the body. It serves for creeping and adhering to substratum.
  11. 11. • Mantle covers greater part of the body and partly covers the edges of shell plates. • Mouth and anus are at opposite ends. • Sexes are separate. Development includes trocophore larva.
  12. 12. Turitella: • Commonly known as ‘sacred shell’. • It is found distributed in intertidal zones of sand and muddy shores and sometimes in estuaries and backwaters. • It has spirally coiled shell with more length than breadth. • Foot is conical and helps in efficient burrowing. • Head bears a pair of tentacles. • It feeds on detritus particle.
  13. 13. Dentalium: • Commonly known as ‘tusk shell’ • They are marine, found in sand at greater depth. • Body is bilaterally symmetrical and enclosed in a tubular shell that opens at both ends. • Mantle folds are fused ventrally to form a tube enclosing a body. • Head is bearing the mouth which is surrounded by contractile tentacles with sucker like ends.
  14. 14. • Foot is long and conical, provides through the anterior opening of shell and used in burrowing. • Gills are absent, respiration by transverse folds in the lining of mantle.
  15. 15. Arca: • Commonly known as ‘arc shell’ • Found distributed in the intertidal and subtidal zones of sandy shores. Sometime found washed in great numbers in the shores. • Shells bear raised and vertically angled umbo. • Bold lines are present on the surface of the wall. • Both the walls are hinged by special ligaments and siphons are lacking. Ventral side of the shell bears a row of teeth and the arrangement is called homodentition.
  16. 16. Meritrix • Commonly known as ‘back water clams’. • Shells are strong, bear number of lines of growth. • Both the shells are hinged by ligaments. • Two pairs of gills are present. • It is a filter feeder and feeds on particulate matter. • These muscles have the tendency to accumulate toxins present in dinoflagellates.
  17. 17. Classification of Phyllum Mollusc Class 1 Pelecypoda or Bivalvia • Habitat: mostly marine • They burrow in mud and sand. • Symmetry: bilateral and the body is laterally compressed. • No distinct head • Examples: Mussels, Unio, Mytilus,
  18. 18. Class 2 Gastropoda • Habitat: These are either aquatic or terrestrial • They possess a spiral shell. • The foot is large and flat. • Head is well developed with tentacles and eyes. • Examples: Hilex (Snail), Limax (Slug), Pila (Apple snail)
  19. 19. Class 3 Cephalopoda • Habitat: mostly marine. • They are adapted for swimming. • The foot is modified into eight to ten long tentacles in the head region. • The shell is either external, internal or absent. • Examples: Octopus, Loligo, Sepia, spirula, Nautilus
  20. 20. Class 4 Monoplacophora • Habitat: exclusively marine • Head is present without eyes and tentacles • Gills are external • Excretion: by serially arranged nephridia
  21. 21. Class 5 Amphineura • Habitat: mostly marine • Body is elongated • Eye and tentacles are absent • Radula is present • Examples; Chiton, Neomenia
  22. 22. Class 6 Scaphopoda • Habitat: marine • Body is bilateral symmetry elongated and enclosed in tusk shell • Foot is reduced • Excretion: a pair of Kidney • Examples: Cadulus, Dentalium
  23. 23. Study of Coelenterata
  24. 24. Characteristic features • Coelenterata includes animal phyla Cnidaria ( true jellies, sea anrmones, corals, sea pens) and Ctenophora (comb jellies). • They are aquatic animals and are mostly found in marine environments and few are found in freshwater habitats. • They can be solitary or live in colonies. Each individual is a zooid. They are sedentary or free swimming. • These are typically invertebrate multicellular organisms, which show a very simple level tissue organization. • They are diploblastic, with two layers of cells, an outer layer called the ectoderm and the inner layer called the endoderm.
  25. 25. • These organisms show two morphological forms – Polyps and Medusa.
  26. 26. • The bodyform is radially symmetrical. • The body has a single opening, through which food is taken in and also waste is expelled out. • The opening in the body is surrounded by tentacles. • Tentacles have special structures known as the nematocysts which help in capturing and paralyzing prey. • Coelenterates do not have sensory organs. • Respiration and excretion occur through simple diffusion. • circulatory system is absent. • Asexual reproduction is seen in polyps, through budding and sexual reproduction is seen in medusa form, through gametic
  27. 27. Classes of Coelenterata Class : Anthozoa • They are exclusively polypoid Class : Hydrozoa • They exhibit polymorphism. There are two main types of zoods, the polyp and medusa . Class : Schyphozoa • They are true medusae
  28. 28. Fungia: • Commonly known as mushroom corals • They are mostly solitary, marine in habitat, some attaining 30 cm in diameter. • They are found in various bright colours including white, pink, red, purple, blue and yellow. • Large in size, discoid corallite, convex on upper and concave in lower surface. • Septa are numerous and connected together. • Adult animal bears a single polyp with many
  29. 29. Phylum : Cnidaria Class: Anthozoa Family: Fungiidae Genus: Fungia
  30. 30. Favia: • They are colonial corals, either dome shaped or flat. • They are marine and reef building stony corals. • Favia was originated in Jurassic period and it is still living today quite successfully. • There is a great diversity of form even among individuals of the same species. • In most species, the corallites are plocoid and in some, monocentric. • septa and costae linked to the corallite wall are well developed and covered by fine teeth.
  31. 31. Phylum : Cnidaria Class: Anthozoa Family: Mussidae Genus: Favia
  32. 32. Gorgonia: • Commonly known as sea fan. • It is a marine, colonial shallow water anthozoa. • Colony is yellowish / reddish in colour and consists of plant like branching stems and a short main trunk attached to the substratum. • Colony branches only in one plane in a feathery manner. • The base of the colony expanded to form hold fast organ. • Axial rod is made up of flexible horn like material gorgonium which is ectodermal in
  33. 33. Phylum : Cnidaria Class: Anthozoa Family: Gorgoniidae Genus: Gorgonia
  34. 34. Tubipora: • Commonly known as organ pipe corals. • It is a marine, colonial polyploid most common in coral reefs. • Colony is reddish in colour and consists of large numbers of vertical CaCO3 tubes of different sizes. • The tubes are connected with transverse platforms formed by fusion of polyps spicules and contain polyps. • Polyps are green in colour but skeleton becomes dull red due to presence of iron salts.
  35. 35. Phylum : Cnidaria Class: Anthozoa Family: Tubiporiidae Genus: Tubipora
  36. 36. Metridium : • Commonly known as Sea anemone. • It is a marine form, large sessile, brightly coloured solitary flower like form. • Sessile polyp attached at the base to the surface beneath it by an adhesive foot, called a basal or pedal disc, with a column-shaped body topped by an oral disc. • Most are from 1 to 5 cm (0.4 to 2.0 in) in diameter and 1.5 to 10 cm (0.6 to 3.9 in) in length, but they are inflatable and vary greatly in dimensions. • The oral disc has a central mouth, usually slit- shaped, surrounded by one or more whorls of
  37. 37. Phylum : Cnidaria Class: Anthozoa Family: metridiidae Genus: Metridium
  38. 38. Pennaluta : • Commonly known as Sea pen / sea feather. • It is a marine, sedentary and colonial form. • Colour is usually red and the fully developed colony measures about 10 cm in height. • The colony is elongated, feather-like and is differentiated into a lower peduncle or stalk and an upper rachis. • The rachis is narow at two ends, dialated in the middle and bears two rows of lateral branches— the pinnules. • Each pinnule is a long, slightly curved, flattened and fleshy projection of the rachis and bears, along its upper margin, a row of anthocodia—the autozoids.
  39. 39. Phylum : Cnidaria Class: Anthozoa Family: Pennatuliidae Genus: Pennatula