Question

What are the key characteristics for the organisms in the phylum Echinodermata. What are the sub groups, and provide an example of each.

Answer 1

The name Echinodermata comes from the Greek word for 'spiny skin,' and if you look closely at a member of the phylum, you'll see that the name is more than appropriate.

In one form or another, all echinoderms are covered in some form of bumps (starfish), spikes (sea cucumbers), or spines (sea urchins). Even sand dollars are covered in bumps when they are alive, though these features aren't as prominent in the dry, preserved form of sand dollar that most people encounter. Echinodermata is a phylum of many unique and beautiful sea creatures which all share a set of common defining traits.

They live exclusively in marine systems; they are widely divergent, with over 7,000 known species in the phylum.
Echinoderms have pentaradial symmetry and a calcareous endoskeleton that may possess pigment cells that give them a wide range of colors, as well as cells that possess toxins.
Echinoderms have a water vascular symmetry composed of a central ring of canals that extend along each arm, through which water circulates for gaseous exchange and nutrition.
Echinoderms have a very simple nervous system, comprised of a nerve ring at the center and five radial nerves extending outward along the arms; there is no structure resembling a brain.
They are hermophrodite, release their eggs and sperm into the water; here, the sperm will fertilize the eggs.
Echinoderms can reproduce asexually by regeneration.
Key Terms:
Madreprorite: a lightcolored calcerous opening used to filter water into the water vascular system of echinoderms
Podocyte: cells that filter the bodily fluids in echinoderms
pentaradial symmetry: a variant of radial symmetry that arranges roughly equal parts around a central axis at orientations 72 degrees.

Water vascular system: a hydraulic system used by echinoderms, such as sea stars and sea urchins, for locomotion, food and waste transportation, and respiration
Ampulla: the dilated end of a duct.

CLASSES OF PHYLUM ECHINODERMATA:

Generally there are five different classes

1. Class CRINOIDEA: It falls under the subphylum Pelmatozoa and have one order of Articulata. The animals are both extinct and living forms. Examples are Antedon, Metacrinus, Rhizocrinus etc.

2. Class HOLOTHUROIDEA: It comes under subphylum Eleutherzoa and have 5 orders namely Aspidochirota, Elasipoda, Dendrochirota, Malpadonia, Apoda. Examples are Holothuria, Mesothuria, Deima, Thyone, Molpadia, synapta, cucumaria etc.

3. Class ECHINOIDEA: It has three subclasses viz. Bothriocidaroida, Regularia(orders: Lepidocentroida, Cidaroidea, Aulodonta, Camarodonta) and Irregularia(orders: Clypeastroida, Spatangoida. Examples are Lovenia, Cidaris, Phormosoma, Echinus, Laganum etc.

4. Class ASTEROIDEA: It have three orders namely Phanerozonia, Spinulosa and Forcipulata. Examples are Luidia, Astopecten, Aesterina, Asterias etc.

5. Class OPHIUROIDEA:  It has two orders: Ophiurae and Euryalae. ExamplECTes are Ophioderma, Astoporpa, Ophiotherix etc.