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CLASSIFICATION OF ECHINODERMATA

CLASSIFICATION OF ECHINODERMATA. Phylum Echinodermata. Sub-phylum : 1. Crinoza. 2. Asterozoa. 3. Echinozoa. Classes: 1. Crinoidea [sea lilies , sea feathers]. Asteroidea [Star fishes] Ophiuroidea [Brittle stars]. Holothuroidea [sea cucumbers]

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CLASSIFICATION OF ECHINODERMATA

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  1. CLASSIFICATION OF ECHINODERMATA

  2. Phylum Echinodermata Sub-phylum : 1. Crinoza 2. Asterozoa 3. Echinozoa Classes: 1. Crinoidea [sea lilies , sea feathers] Asteroidea[Star fishes] Ophiuroidea[Brittle stars] Holothuroidea [sea cucumbers] Echinoidea [sea urchins , heart urchins, cake urchins, sanddollars]

  3. Class Crinoidea The salient features crinoidea are the following Body is stalked or stalkless and pentamerous and consist of an aboral cup and a oral cover .The cup is called calyps or disc , and the cover is called Tegmen. Mouth and anus are located on the upper side. Arms are long and movable ,branched or unbranched , and with or without alternating bilateral processes , called Pinnules. Ambulacral grooves are open and ciliated and they extend up to the tip of arms and pinnules. Madreporite, spines and pedicellariae are absent. Tube feet have no suckers . Sessile forms have aboral , jointed and heavily calcified stalk for attachment. Sexes are separate, developments is indirect with a barrel shaped larava called doliolaria . Eg:- Antedon , Diplocrinus, Metacrinus, Rhizocrinus.

  4. Class Asteroidea Asteroids are flattened and free living echinoderms, commonly called Star fishes or sea stars.Their salient features are the following: Spiny , flat and pentaggonal body with a central disc , 5-20 or more radial arms or rays, and distinct oral and aboral surfaces . Mouth and ambulacral grooves are on the lower side , and annus and madreporite are on the upper side . Ambulacral grooves are open channels, studded with sucker –bearing tube feet . Dermal ossicles are loose , flexible and separate pieces. Respiratory structures are dermal branchiae or skin gills. Sexes are separate . Development is indirect with bipinnaria and brachiolaria larvae. There are nearly 1500 species of living asteroids . They enjoy worldwide distribution , especially in coastal waters. EG:-Asterias, Asteropecten, Pentaceros, Solaster, Echinaster.

  5. Class Ophiuroidea Ophiuroidea comprises the echinoderms , popularly known as basket stars , brittle stars , or serpent stars . The major characteristics of ophiuroids are following: Flat body , with a thin disc and five or more slender and flexible arms. Arms are formed of a series of segment-like sections or articles , each article being formed of four shields. Ambulacral grooves, pedicellariae and dermal branchiae are absent . Tube feet are without ampullae and suckers. Gut is a blind sac, without intestine and anus . Madreporite is on the oral surface. Sexes are separate .development is indirect with a lava called ophiopluteus. Many ophiuroids have the powers for autotomy (self multilation) and regeneration . Ophiuroidea is the largest class of echinoderms with nearly 2000 described species . EG:- ophiothrix, Ophiocoma, Ophioderma , Ophiolepis, Gorgonocephalus

  6. Class Holothuroidea Holothuroidea is a group of leathery and almost cylindrical echinoderms , commonly called sea cucumbers. The major diagnostic features of holothurroids are the following: Body is long , cylindrical and almost bilaterally symmetrical . Body wall is leathery and dermomuscular. Mouth and anus are at opposite ends. Mouth is encircled by crown of retractile tube feet, known as buccal podia , which are modified as oral tentacles. Radial arms, spines and pedicellariae are absent. Dermal ossicles are microscopic , vestigial and loosely scattered. Ambulacral grooves are absent and madreporite is internal. In most cases, madreporic canals have no external openings or hydropores . Alimentary canal iss long and coiled , with definiteecloaca. Connected to the cloaca are the so-called respiratory trees or cloaca gills. Circulatory system is more advanced than that of other echinoderms, and it functions to transport oxygen , and perhaps nutrients also. Development is indirect with characteristic larva, called auricularia. EG:-Holothuria,Mesothuria, Cucumaria, Thyone, Synapta, Synaptula.

  7. Class Echinoidea Echinoidea includes echinoderms popularly called sea urchins, heart urchins , cake urchins,and sand dollars. There are 950 species of known echinoids. The salient features of echinoidea are the following: Body is globular , oval , discoidal, or heart shaped with definite oral and aboral surfaces. Arms and ambulacral grooves are absent. The whole body is enclosed in a box-like shell , known as corona or test.it is formed of calcareous plates. Borne on the test , and covering the whole body , is an armature of movable spines . Mouth is surrounded by leathery membrane , called peristome ,and anus by periproct. Mouth is armed with a characteristic chewing apparatus called Aristotle’s lantern. Arranged in between the spines and extending between peristomeanddperiproct , are five double rows of tube feet. Sexes are separate .development is indirect with a characteristic larva , called echinopluteus. EG:-Salmacis, Echinus , Echinocardium, Echinodiscus, Clypeastear.

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