Phylum Echinodermata: General Characteristics and Classification




Phylum Echinodermata

Phylum Echinodermata: General Characteristics and Classification

General characteristics of Phylum Echinodermata

  1. (Echinos: Spines; derma: Skin)
  2. Kingdom: Animalia
  3. Habitat: These are exclusively marine
  4. Grade of organization: organ system grade
  5. Germ layer: triploblastic
  6. Symmetry: Adults are radially symmetrical while the larvae are bilaterally symmetrical.
  7. Coelom: present ( coelomate)
  8. Body without segmentation
  9. The shape of the body is flat, star like, spherical or elongated.
  10. Head is absent
  11. Presence of tube feet
  12. Presence of water vascular system
  13. Mouth is present on ventral side while anus is present on dorsal side
  14. Respiration: by papule, gills or clocal respiratory tree
  15. Nervous system: absent, they are brainless organism.
  16. Circulatory system: is reduced, heart is absent
  17. Blood has no pigment.
  18. Digestive system: complete
  19. Excretory system: absent
  20. Sexes: mostly dioecious, rarely monocious
  21. Reproduction:
  • Sexual: by gamatic fusion
  • Asexual: regeneration
  1. Fertilization: external
  2. Development: indirect with characteristic larvae

 

Classification of phylum Echinodermata

It is divided into 5 classes:

  1. Asteroidea
  2. Ophiuroidea
  3. Echinoidea
  4. Holothuroidea
  5. Crinoidea

Class 1 Asteroidea

  • Body is flattened star shaped with five arms
  • They possesses tube feet with a sucker
  • Presence of calcareous plates and movable spines.
  • Respiratory organ: papulae
  • Examples: Asterias (Star fish), Astropecten, Zoraster, Oreaster

 

Class 2 Ophiuroidea

  • Body is flat with pentamerous disc
  • They possess a long arm which is sharply demarcated from the central disc.
  • They possesses tube feet without sucker
  • Anus and intestine are absent
  • Respiratory organ: Bursae
  • Examples: Ophiderma, ophiothrix, Astrophyton, Amphuria, etc

 

Class 3 Echinoidea

  • Body is disc-like hemi-spherical
  • They are devoid of arms or free-rays.
  • They possesses tube feet with a sucker.
  • They possess compact skeleton and movable spines.
  • Examples: Echinus (Sea urchin), Cidaris, Arbacia, Echinocardium. Diadema

 

Class 4 Holothuroidea

  • Body is elongated in the oral-aboral axis and it is like cucumber.
  • They have no arms, spines and pedicellariae.
  • The tube feet are sucking type which is modified into tentacles and form a circle around mouth.
  • Respiratory organ: cloacal respiratory tree
  • Examples: Cucumaria (Sea cucumber), Holothuria, Mesothuria, etc

 

Class 5 Crinoidea

  • Body is star shaped
  • Some of the forms were extinct and living forms.
  • Arms bifurcated, with two pinnules.
  • They have tube feet without suckers
  • Examples: Neometra, Antedon, Rhizocrinus, etc

Phylum Echinodermata: General Characteristics and Classification