To study the classification with reasons of the phylum Echinodermata.
Phylum - Echinodermata
The name Echinodermata literally means ' Spiny skinned animals '. Echinodermata name derived from Greek ; echinus- spiny, derma - skin . The skin or test of these animals bears prominent spines.
General Characters of Echinodermata :
1)Echinoderms are exclusively marine animals. They are gregarious, mostly free-living, slow-moving (creeping), Some are Pelagic and few are fixed.
2)Animals show pentamerous radial symmetry & larvae show biradial symmetry.
3)Body shape may be star-like, globular spherical, discoidal or elongated, flattened with oral & aboral surface.
4)Ambulacral grooves are present on the body surface.
5)Endoskeleton consists of closely fitted plates forming a shell. These plates are hard & calcareous , Exoskeleton is made up of movable calcareous spines.
6)Body cavity or coelom is large, lined by ciliated peritoneum.
7)Presence of water vascular or ambulacral system is the characteristic feature of echinoderms. Sieve Plate like madreporite is present which is hydropore.
8)Tube feet or podia are useful for locomotion, food capture and respiration.
9)Respiration occurs through variety of structures such as papulae (skin gills), Peristomial gills, genital bursae and cloacal respiratory trees.
10)Circulatory system is reduced and lacunar.
11)Heart is absent.
12) Excretory system is wanting.
13) Nervous system is primitive.
14)Sense organs poorly developed & consist of statocysts, eye-spots & tentacles.
15)Sexes are separate, no sexual dimorphism.
16)Reproduction is entirely sexual, fertilization external.
• Phylum Echinodermata have two sub- phylum:-
A) Eleutherozoa B) Pelmatozoa
• Eleutherozoa contains four classes:-
1) Asteroidea - e.g. Pentaceros
2) Ophiuroidea - e.g. Ophioderma
3) Echinoidea - e.g. Echinus
4) Holothuroidea - e.g. Holothuria
• Pelmatozoa contain only one class:-
1) Crinoidea - e.g. Antedon
1)Class : Asteroidea :-
(Aster or asteroeides-star like)
e.g. Pentaceros
Phylum: Echinodermata - Radially symmetrical, spiny skin, with water vascular system.
Sub-phylum: Eleutherozoa - Free living, mouth on oral surface , tube feet with suckers.
Class: Asteroidea - Star shaped body,
ambulacral groove with tube feet.
Family: Oreasteridae - Five arms around stiff, convex & Often brightly colored body.
Genus: Pentaceros
Species: nodosus.
2)Class: Ophiuroidea
(based on genus ophiura,
Greek ophis = snake + oura - tail)
e.g. Ophioderma (Brittle star)
Phylum: Echinodermata- Radially symmetrical, spiny skin, with water vascular system.
Sub-phylum: Eleutherozoa - Free living, mouth on oral surface tube feet with suckers.
Class: Ophiuroidea - Bases of arms distinctly marked off from the disc. No ambulacral grooves, anus & intestine.
Family: Ophiodermatidae - Laterally insected & tapering arms, continuous series of closely set of oral papillae,single series of teeth.
Genus: Ophioderma
Species: anitae
3) Class: Echinoidea
(ekhinos = spine, sea urchins. hedgehog )
e.g. Echinus (Sea urchin)
Phylum: Echinodermata - Radially symmetrical, spiny skin, with water vascular system.
Sub-phylum: Eleutherozoa - Free living, mouth on oral surface, tube feet with suckers.
Class: Echinoidea - Spherical body, enclosed in shell. No ambulacral grooves, anus.
Family: Echinidae - Pedicellariae are globiferous with 1 or 2 pairs of lateral. Teeth, ambulacral plates are compound.
Genus: Echinus
Species: esculentus
4) Class: Holothuroidea
(Holothurum, holos - whole + thureoides - oblong shield / door )
e.g. Holothuria
Phylum: Echinodermata - Radially symmetrical,spiny skin, with water vascular system.
Sub-phylum: Eleutherozoa- Free living, mouth. on oral surface, tube feet with suckers.
Class: Holothuroidea - Cylindrical body, elongated in oral-aboral axis, anus absent.
Family: Holothuriidae - Thick fleshy body, several rows of tube feet, able to eject a mass of sticky threads i.e. cuvierian tubules to distract predators.
Genus: Holothuria
Species: nigra
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