What are Echinoderms?
Echinoderms are aquatic creatures that usually live at the ocean floor. There are currently over 6,000 known species of echinoderms, some of which include:
- Asteroida: eg. sea daisies and sea stars (like Patrick!)
- Ophiuroidea: eg. brittle stars
- Echinoidea: eg. sea urchins and sand dollars
- Crinoidea: eg. sea lilies and feather stars
- Holothuroidea: eg. sea cucumbers (5).
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Ophiroidea- Brittle StarsBrittle Stars are characterized long, flexible arms. Its respiratory device consists of ten sac between the pouches of its stomach. Each sac opens through a slit to allow the flow of oxygen and carbon dioxide. The current along these slits is pushed along by flagellae, which are similar to the cilia of the sea stars (3).
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Crinoidea- Sea Lilies and Feather StarsCrinoids have the simplest respiratory systems among the echinodermata. They have simple water vascular systems that maintain hydraulic pressure in the tube feet. This is connected only to the body cavity. Crinoids also have a separate haemal system with fluid-filled sinuses within the connective tissue in the body cavity. The haemal system transports respiratory gases from the tube feet to the rest of the body. Oxygen is absorbed through the thin-walled tube feet.
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Evolution
The evolutionary history of the echinoderm dates back to the early Cambrian and from there rapidly diversified. Genetic studies suggest that echinoderm evolution occurred by means of extensive mutation in regulatory genes inherited from bilateral ancestors. Tube feet were used for respiration in early ancestors of echinodermata. The four non-crinoid classes have similar structure and function in their water vascular systems. Their intricate network of canals could have been built upon pre-existing anatomical structures, such as the lophophore and U-shaped gut of a lophophate-like common ancestor. The water vascular system probably arose as a feeding structure in early sessile echinoderms, as evidenced by fossil interpretations, and secondarily became used for locomotion. Another interpretation may be that the system evolved more than once among extinct and extant echinoderms for different purposes such as respiration, feeding, or locomotion. (4)
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(1) "Phylum Echinoderm." Echinoderms. MCWDN- Marine Biology Institution, n.d. Web. 14 June 2016.
(2) Ilyes, Laszlo. "What Is the Respiratory System of a Starfish?" Reference. IAC Publishing Labs Company, 2016. Web. 15 June 2016.
(3) "Echinodermata." The Columbia Encyclopedia, 6th Ed.. 2016, Brian R. West, Michael Allaby, AILSA ALLABY;MICHAEL ALLABY, and "Echinodermata." A Dictionary of Biology. 2004. "Echinodermata."Encyclopedia.com. HighBeam Research, 01 Jan. 2016. Web. 15 June 2016.
(4) Zelnio, Kevin. "Veins of Water: The Evolution of the Echinoderm Water-Vascular System." Veins of Water: The Evolution of the Echinoderm Water-Vascular System. Deep Sea News, 20 Mar. 2012. Web. 15 June 2016.
(5) Reece, Jane B., Lisa A. Urry, Michael L. Cain, Steven Alexander Wasserman, Peter V. Minorsky, Rob Jackson, and Neil A. Campbell. Campbell Biology. 10th ed. New York: Pearson Education, 2014. 707-09. Print.
(2) Ilyes, Laszlo. "What Is the Respiratory System of a Starfish?" Reference. IAC Publishing Labs Company, 2016. Web. 15 June 2016.
(3) "Echinodermata." The Columbia Encyclopedia, 6th Ed.. 2016, Brian R. West, Michael Allaby, AILSA ALLABY;MICHAEL ALLABY, and "Echinodermata." A Dictionary of Biology. 2004. "Echinodermata."Encyclopedia.com. HighBeam Research, 01 Jan. 2016. Web. 15 June 2016.
(4) Zelnio, Kevin. "Veins of Water: The Evolution of the Echinoderm Water-Vascular System." Veins of Water: The Evolution of the Echinoderm Water-Vascular System. Deep Sea News, 20 Mar. 2012. Web. 15 June 2016.
(5) Reece, Jane B., Lisa A. Urry, Michael L. Cain, Steven Alexander Wasserman, Peter V. Minorsky, Rob Jackson, and Neil A. Campbell. Campbell Biology. 10th ed. New York: Pearson Education, 2014. 707-09. Print.