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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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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]


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.


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.


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


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.


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 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.