Tuesday, May 09, 2006

THE WATER VASCULAR SYSTEM THAT CHARACTERIZES ANIMALS THAT OCCUR IN THE PHYLUM ECHINODERMATA

Enchinodermata are a phylum of marine animals found in the ocean at all depths. The echonodermata has six classes which are Asteroidea example starfish, Concentricycloipea example sea daises, Crinoidea example feather stars, Echonoidea example sea urchin, Holuthuroidea example sea cucumbers and Ophiuroidea example brittle stars. The phylum is containing approximately six thousands species and constitute the group of deuterostome invertebrates. Enchinodermata are characterizes by a unique vascular system.

The vascular system can be defined as a hydraulically controlled system consisting of a circumoral ring around the esophagus with connecting radial canals each leading to an ambulacrum. The vascular system can be closed and opened. Crinoids have an open vascular system. The water vascular system is used by echinoderm such as sea stars and sea urchins. They may be evolved from tentacular system similar to those of deuterostone phyla such as tentacle pterebranch hemichordates. However there are different kinds of derived features of the vascular system, these include an embryological origin from left mesocoel, podia arranged along branches (ambulacra), and a central curcumesophagel ring.

The characteristics of vascular system do differ according to class. Crinoid has madreporite with multiple pores and madreporite may be replaced by minute scattered openings called hydropores. It has no polian vesicles, tube feet suckers and ampullae on podia. Podia penetration is between plate and podia spacing is stumble. In asteroid madreporite of vascular system has aboral. Some asteroid have tube feet sucker whereas others do not have. Podia penetration is between plates. It has ampullae on podia.

In Ophiuroid, madreporite of vascular system has oral. It has a polian vesicles Ophiuroid does not tube feet sucker. Podia penetrations are found between plates. Podia spacing is paired. It does not have ampullae on podia. In Echinoid madreporite has aboral. It has polian vesicles, tube feet sucker may be present or absent. Podia penetration is paired through plates. Podia spacing is stagger. It has ampullae on podia. In Holothuroid madreporite are internal. It has polian vesicles. Tube feet sucker a may be present or absent. Podia penetration between suckers may be present or absent. Podia penetrations are found between plates. Podia spacing is stagger. It has ampullae on podia.


Vascular systems network canals to create hydrostatic pressure, to help the starfish to move. Water enters through sieve plate or madreporite on aboral surface into a short stone canal. Stone canal connects to a circular canal around the mouth called the ring canal. Five radial canals carry water to hundreds of paired tube feet. Bulb-like sacs or ampulla’s on the upper end of each tube foot contract and form suction to help move, attach or open bivalves’ mollusk shells and create suction to pull valves apart slightly. Starfish exerts its stomach through its mouth and inserts into prey. Stomach secretes enzymes to partially digest bivalve then stomach withdrawn and digestion completed inside the starfish.

The vascular systems perform different functions in echinoderm; these include locomotion, respiration, and feeding. Most of the sensory neurons are located at the podia which are also part of this organ. Most oxygen enters starfish through diffusion into the tube feet. This water vascular system can be used as a source of oxygen for respiration. Many sea cucumbers also have a complex respiratory tree. The surface of many echinoderms is perforated by extensions of the body wall. Through these thin membranes of the body wall respiration can take place.

The vascular systems are very essential to echonodermata. They are responsible for digestion, locomotion and respiration. Even though echonodermata do differ with some characteristics but they all have vascular system. The vascular system is either open or close.

References

Denning D & Russell B. The Biology of Echinoderms [Internet] 2006 May 05, 12:30 UCT [cited 2006 May 07] Available from: http://ebiomedia.com/prod/BOechinoderms.html%202000-2005

Wikepedia Contributors. Water vascular system [Internet] Wikipedia, The free Encyclopedia, 2006 May 05, 11:15 UCT [Cited 2006 May 07] Available from: http://en.wikipedia.org/wiki/water vascular

Gregory A.W. Echinodermata. [Internet] 2006 May 05, 14:10 UCT Available from: http://tolweb.org/Echinodermata
Masiya Kedibone
CSIR PTA
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