Phylum Echinodermata : General Characters, Examples

 

Defination

• Echinoderms  are  marine  animals with spiny bodies bodies having calcareous ossicle.

• This is  phylum which have close  relationship with chordates .

General characters 

• They are endoskeleton of calcareous ossicle and look spiny therefore they called as Echinoderms.

• They are exclusively marine. 

• They are Coelomate, Triploblastic with organ system level of organisation .

• The  adults Echinoderms are radial symmetrical but larva possess bilateral symmetry.

• Digestive system is complete. Mouth is located on ventral side and anus is present on dorsal side.

• Water vascular system or Ambulacral system is most distinctive feature of Echinoderms.

• Water vascular system is involved in Respiration, transportation of food and capturing of prey.

• Excretory system is absent in Echinoderms.

• Saxes are separated. They reproduce only sexually. Fertilisation is usually external.

• Development is indirect with free swimming larva.

Examples of Echinodermata

1. Ophiura

• It is also known as Brittle star.

• Body is divided into oral and aboral surface.

• Central disk and arms are quite distinct.

• It has considerable change in spine armature and color pattern.

• Aboral surface has radial shield in Central disk.

• Mouth in oral surface has complicated system of  plates spine tube feet.

• At the base of each arm, bursal slits are present.

• Central disk has endoskeleton of calcium carbonate and present also in internal organs.

2. Cucumaria

• It is also known as sea cucumber.

• Oral end contains whorl of 10 dendrite and pinnately branches tentacles around the mouth. Tentacles are modified tube feet.

• Anterior end contains collar which contain mouth.

• Rest  of body  is divided into five Ambulacral groove and five inter Ambulacral groove.

• Aboral surface has radial shield in Central disk.

• Mouth in oral surface has complicated system of  plates spine tube feet.

• Tube feet when present contain suckers.

• .Body wall contain very  small seprate ossicle.

• Larval is Auricularia or Doliolaria.

3. Echinus

• It is also known as sea urchin.

• Body is differentiated into flat oral and dome shaped aboral surface.

• Anterior end contains collar which contain mouth.

• Body is enclosed by globular test which contain calcareous plates.

• Entire surface of body is covered by the movable articulated spines except peristome and periproct.

• Mouth in oral surface has complicated system of  plates spine tube feet.

• Pedicellariae and sphaeridia are defensive and offensive organ.

• Oral surface contain mouth from where jaw apparatus or Aristotle lantern are spread internally for mastication.

5. Antedon 

• It is also known as sea lily or feather star.

• On aboral surface,   calyx bear knob like structure called centro dorsal plates.

• Calyx is differentiated into oral surface that bear mouth and anus and aboral surface in which arms and cirri are inserted.

• Aboral surface is covered by leathery skin in  which  calcareous plates are inserted.

• On aboral surface , calyx bear a knob like structure called as stung of stalk.

• Mouth is central and directly upward to lead into five Ambulacral groove.

• Water vascular system is well developed but madreporite are absent.

• There are ten arms which contain numerous pinnules containing gonads. 

5. Asterias 

• It is also known as  star fish.

• Body is radial symmetrical, star shaped and pentagonal.

• Body or central disk can be identified that  Mouth is located on ventral side and anus is present on dorsal side.

• Central disk in continued up to five arms.

•  Aboral surface contain conical spines over the surface and over the sub pentagonal madreporite plate.

• Pedicellariae are present on aboral surface.

• Water vascular system is well developed but madreporite are present.

• Terminal tube feet is photosensitive.