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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Sub-phylum : 1. Crinoza
Classes: 1. Crinoidea
[sea lilies , sea feathers]
Holothuroidea [sea cucumbers]
Echinoidea [sea urchins , heart urchins, cake urchins, sanddollars]
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.
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.
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
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.
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.