Lizzy

I am Masingita Lizzy Maluleke.I did Bachelor degree of Enviremental Sciences at the University of Venda for science and technology majored with Geography and Ecology and Resourse Managenment.I am presantly doing honours with the university of the Western Cape in Ecological Informatics.

Wednesday, May 10, 2006

THE WATER VASCULAR SYSTEM THAT CHARACTERISES ANIMAL THAT OCCUR IN THE PHYLUM ECHINODERMATA


The water vascular system is a system of canal branching through the body that branch in many sections known as tube feet which era also 2 000. These tube feet can penetrate the body wall and skeleton in ambulacral grooves in enchinoders. Water vascular system also refers to the hydraulic system used by an enchinoderms such as sea fish and sea urchins. The water vascular system develops from tentacular system and it has feature such as podia arranged along the branches, an embryological origin from left mesocoel and central circumesophageal ring.


The important functions of water vascular system in echinoderms are for locomotion, respiration and were transportation as well as feeding. The water found in pore, in the body wall of an echinoderms are very important for feeding and respiration and this indicate that this system is an internal closed system of reservoirs and ducts containing water fluid. The water vascular system is also the canal that joins all the canals creating hydrostatic pressure to help the star fish to move. The water inside this system move through modreporite on aboral surface and go straight to the stone canal, which connects to a circular canal around the mouth known as ring canal.


These animals have five radial canals which are extend down each arm and they are connected to the ring canal. These radial canals transport water to the tube foot which contract and create suction to help these animals to move and attach or open bivalves. Their stomach secretes enzymes to digest bivalve, so the stomach withdrawn and the digestion takes place in the stomach of star fish. This system has separate sexes. They have two gonads in each arm and these gonads produce eggs or sperm. They only have external fertization. The females produce about 200 000 000 eggs per season and fertilized eggs produce into bipinnaria larva which live to the bottom of a sea after two years and changes into adult. They have an asexually which by reproduced by regenerating arm.


The water vascular system use cilia and ampullae to keep things moving. An Ionic imbalance causes water to flow into madreporite and also allow water to inter to the water vascular system. Some of the water is directed to the different part of the animals such as coelon. Some of the water directed where it is circulated by the beating of cilia. Phylum Echinodermata are marine animals such as sae star, sand dollar, sea urchins, brittle star and sea cucumber and they are found in the ocean. These animals are also known as spiny-skinned animals and they are also endoskeleton made by calcium plate or ossicles with protruding spines.


Echinodermata are free-swimming larva to sessile and undergo metamorphosis from bilateral. The larva stage known as a bipinnaria and the adults have pentaradia symmetry. They have a segmentation or metamerism and they have coelomate. They use skin gills for breathing and they are capable of extensive regeneration. Bipinnias mouth is found at the oral surface which is the lower surface and its anus is at the aboral surface which is the upper surface. Bipinnaria do not have head or brain, they have a nervous system. They have tube feet as an arm which helps them to move and eat. Echinordermata divided in to five classes and are as follow.


Asteriodea class are star fish or sea fish. Their body have more arms. They are predators in much marine system and also prey on bivalve molluses such as clams and oysters. They have five arms projected from the central disk that can be regenerate. They have mouth on the oral surface. Crinoidea class are animals such as sea lilies and feater stars which are most primitive of the echinoderms. They have long stalk with branching arms that attach them to rock and the bottom of the ocean. Their mouth and anus are located on the upper surface. They have 5 to 200 arms with sticky tube feet to help them to capture the food and take in oxygen. They are also nocturnal feeders.


Echinodea are animals such as urchins and dollars. They do not have arms and their bodies are covered with movable spines and they use tube feet to move. Sea urchins and sand dollars also have differences. Sea urchins have a spherical shape, and sand dollars have flattened body. Urchins live in the bottom of the ocean, and dollars live where there is sand along the coastlines. Holothuroidea are animals such as sea cucumbers and they are found at the bottom of the ocean and hide themselves during the day. These animals do not have arms; they have a soft body with a tough and leathery outer skin. They can scare predators by ejecting part of their internal organs and regenerate this structure during the day.


The last class is ophiuroidea. These are the animals such as basket stars and brittle stars. These animals are found on the bottom of the oceans under stone and in holes. They have long and narrow arms which resemble tangle of snakes. They move faster than a star fish and they feed themselves by standing in the food with arms.


References:

Wikipedia contributors. Water vascular system [internet] wikipedia, The Free Encyclopaedia, 2006 May 8, 12:13 UCT. Available from: http://en.wikipedia.org/wiki/Water-vascular-system


Lizzy Maluleke
CSIR PTA
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Cell number 072 351 8488
Tell [012] 841 2133
Fax [012] 842 3676
E-mail mmaluleke@csir.co.za
Weblog: http://mmaluleke.blogspot.com

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