Echinodermata

Subject: Biology

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Overview

This note provides information about Echinodermata with its characters and types. they are coelomate animals. in this Echinodermata includes the coelom, body forms, water vascular system, locomotion, digestive system, reproduction, development.
Echinodermata

source:tolweb.org example of phylum echinodermata
source:tolweb.org
example of phylum Echinodermata

Echinos→ spine

derma → skin

Jacob Klein introduced the term Echinodermatain 1734.

General characteristic feature of phylum Echinodermata:

  • They are exclusively marine, not found in Nepal.
  • The body possesses numerous spines, five radiating ambulatory groups used for protection to the body.
  • They are triploblastic and radial symmetrical ( larval forms are bilaterally symmetrical.)
  • They are coelomate animals. Coelom is the enterocoelous type.
  • The body is of various shapes like globular, star-shaped, spherical, elongated and flattened. The distinct head is absent. The body has distinct oral and aboral surfaces. The body surface is marked by five radiating areas called ambulacral areas.
  • A characteristic feature of echinoderms is the water vascular system. This system helps the animal in feeding, locomotion. It takes place by tube feet. It is present on each arm.
  • The alimentary canal is complete which is coiled or straight. Mouth is present on the oral surface and anus on aboral surface.
  • Respiration takes place through gills or cloacal respiratory trees.
  • Blood vascular system is enclosed in coelomic peri haem channels. Respiratory pigments are absent.
  • The excretory organ is absent.
  • The nervous system is without the brain but a circumoral ring and radial nerves are present. Hence, it is of the primitive type.
  • Sexes are separated. Fertilisation is external. They have the remarkable power of regeneration.
  • It is indirect through free-swimming larval forms such as bipinnaria and auricularia.

Classification:

Phylum Echinodermata is classified on the basis of number and type of arm and form of the body.

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Subphylum-1 Eleutherozoa:

There are the free swimming stemless echinoderms. It has five classes:

Asterias
Asterias

Class-1: Asteroidea

  • The body is star-shaped with five radiating arms, which are not sharply marked off from the central disc.
  • Ambulacral grooves with tube feet.
  • Oral and aboral surfaces are distinct.
  • Example: Asterias
Ophioderma
Ophioderma

Class-2: Ophiuroidea

  • The body is star-shaped having five arms, which are sharply marked off from the central disc.
  • Ambulacral grooves absent or covered with ossicles.
  • The anus is absent.
  • Example: Ophioderma
Echinus
Echinus

Class-3: Echinoidea

  • The body is spherical or disc-like oval.
  • Arms are absent.
  • Ambulacral grooves covered with ossicles.
  • Aristotle's lantern is a masticatory apparatus present.
  • Example: Echinus
Holothuria
Holothuria

Class-4: Holothuroidea:

  • The body is elongated without arm and spine.
  • Mouth surrounded by tentacles.
  • Longitudinalambulacral grooves and scattered ossicles.
  • Example: Holothuria
Subphylum:2 Pelmatozoa ( attached to substratum by stalk)
Antedon
Antedon

Class-5: Crinoidea

  • Usually stalked animal with more or less globular body.
  • Many arms with pinnules forming feathers.
  • Ambulacral grooves and scattered ossicles.
  • Mouth and anus are present on the oral side.
  • Example: Antedon
Things to remember
  • The word Echinodermata means the spiny skin as the members of this phylum bears spines on their body surface.
  • The membersof this phylum are exclusively marine and possess large number  of spines on their body.
  • They posses tube feet for locomotion.
  • Respiratory organs in Echinodermata are dermal branchiae, genital bursae, peristomial gills, cloacal trees and tube feet.
  • There are four sub - phylum of Echinodermata which are Eleutherozoa and Pelmatozoa.
  • The examples of class Asteroidea is star fish, Ophiuroidea is brittle - star, Echinoidea is sea - urchin and Holothurion is sea- cucumber.
  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.

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