ECHINODERMS

In order for an organism to be included in the phylum of echinodermata, they have to be able to consist of the following four synapomorphies (Wray, unknown). Together, these synapomorphies define much of what makes the functional biology of echinoderms distinctive from that of other metazoans (Wray, unknown). Firstly, they must have a calcitic skeleton composed of many ossicles. Echinoderm skeletons are composed of calcium carbonate and several proteins (Wray, unknown). Ossicles are not solid, but have a sponge-like microstructure called stereom that is unique to the phylum (Wray, unknown). Secondly, they must have a water vascular system (Wray, unknown). The water vascular system performs many important functions in echinoderms, including locomotion, respiration, and feeding; in addition, most sensory neurons are located at the termini of podia (tubefeet) which are part of this organ system (Wray, unknown).Thirdly, the body must contain mutable collagenous tissue which provides some interesting mechanical advantages, including the ability to maintain a variety of postures with no muscular effort (Wray, unknown). Lastly, there should be pentaradial body organization in adults (Wray, unknown). The scientific classification of the phylum echinodermata goes as follows.

Kingdom: Animalia
Subkingdom: Metazoa
Superphylum: Deuterostomia
Phylum: Echinodermata
Classes:
Asteroidea
Blastoidea (extinct)
Concentricycloidea
Crinoidea
Echinoidea
Holothuroidea
Ophiuroidea
Source: www.Wikipedia.com

Echinoderms are an ancient group of animals extending back to the Cambrian period (Hickman et al, 2004). Despite an excellent fossil record, the origin and early evolution of echinoderms are still obscure (Hickman et al, 2004). It seems clear that they descend from bilateral ancestors because their larvae are bilateral but become radially symmetrical later in their development (Hickman et al, 2004).


Sea urchins graze kelp and may reach population densities large enough to destroy kelp forests at the rate of 30 feet per month (Anon , 2005). Urchins move in "herds," and enough urchins may remain in the "barrens" of a former kelp forest to negate any attempt at regrowth (Anon , 2005). Sea otters, playing a critical role in containing the urchin populations, prey on urchins and thus control the numbers of kelp grazers (Anon , 2005).

Reference:

Anonymous , (2005) downloaded from http://www.sanctuaries.nos.noaa.gov , 13/03/06
Hickman. P, Roberts. L, Larson. A, I'Anson. H. (2004) Integrated principles of zoology, twelfth edition, McGraw-Hill Companies, pg 443

Wray, G.A (date unknown).downloaded from http://tolweb.org , 11/03/06

www.Wikipedia.com , 11/03/06

 

DALE OVERMEYER

 

2355332

 

696 0309

 

083 272 1002