Echinodermata

What Are Echinoderms? Definition: An invertebrate marine animal usually characterized by a five-fold symmetry, and possessing an internal skeleton of calcite plates, and a complex water vascular system. Includes: chinoids (sea urchins) crinoids (sea lilies) asteroids (starfish) Holothuroids (sea cucumbers) Ophiuroids (basket stars) Sea Urchin

5 Classes of Echinoderms Class Asteroidia: Sea stars or Starfishes have arms that are supported by elements in the body wall, not separable from a central disc. They usually have five arms though some have more. Class Ophiuroidea: Brittle and Basket stars have thin, flexible branching arms that have internal structures for support and not attached to the animals' central discs; use their entire arms, not just tube feet for locomotion. Class Crinoidea: The Sea Lilies and Feather Stars, characterized by having 1) A stalk and being attached to the substrate 2) Erect feeding structures on their upper surfaces. They have upward and outward extending arms supported by calcareous plates. 3) Crinoids are the only ones with their mouths, water-vascular system and anus on the body surface away from the substratum. 4) Semi-rigid bodies restricting them to suspension feeding. Class Echinoidea: Urchins and Sand Dollar, body walls composed of plates with moveable spines and no arms. Their overall shape is globular to oval. 5. Class Holothuroidea: Sea Cucumbers, feeding tentacles extending from their circum-oral feeding ring, wide range of reduction in endoskeletons.

Symmetry, Germ Layers, and Coelum Adults have pentiradial symmetry 3 germ layers Considered “coelomates” because they have a fluid-filled cavity between the body wall and the gut Have well-developed coelum, forming the perivisceral cavity and the cavity of the water-vascular system

Water-Vascular System Enclosed system within the body of an echinoderm that contains many branches and conducts the flow of water, which is mainly drawn into the animal through a perforated plate. Branches extend into the tube feet, which helps with movement in the mobile animals

Movement Mobile echinoderms are slow. Some echinoderms, like sea lilies, don’t move at all Move by using tube feet and pushing with their spines Tube Feet are extended by using hydraulic pressure from water drawn through the water vascular system, and consists of two parts: ampulla and podia. Allow for sticking the floor of the ocean and slow movement Tube feet are used for both movement and feeding Tube Feet of a Starfish: http://www.youtube.com/watch?v=4IRF-pKVtuU

Spines Many echinoderms contain internal spines that are part of the internal skeletal structure and are covered by the epidermis These spines are used in combination with the tube feet to propel the animals forward Some, like the crown of thorns starfish, have many external spines used for protection

Development Begins with a bilaterally symmetrical embryo, with a coeloblastula developing first “Second mouth” forms with gastrulation, the mesoderm moves inwards, and the coelum forms Each taxon produces a distinct larvum, the left hand side of which develops into the adult organism, the right hand side eventually being absorbed; the left hand side typically becomes the oral plate. Blastulas and gastrulas of a starfish

Reproduction and Life Cycle Use both sexual and asexual reproduction Asexual Reproduction: -Used mainly by sea stars and sea cucumbers -Organisms cleave themselves into two or more parts, and then re-grow the missing body parts Sexual Reproduction: Eggs and sperm are released into open water and fertilized externally. The fertilized eggs develop into planktonic larvae and go through two stages: bipinnaria and brachiolaria. Bilaterally symmetrical and have bands of cilia used in swimming and feeding. As the larvae gradually metamorphose into adults, a complex reorganization and degeneration of internal organs occurs. The left side of the larva becomes the oral surface of the adult, which faces down, and the right side becomes the aboral surface, which faces up. The larvae settle to the sea floor and adopt the adult pentaradial symmetry.

Reproduction and Life Cycle (Continued)

Starfish Digestion Digestion is carried out in two stomachs: the pyloric stomach and the cardiac stomach Cardiac Stomach -Can be pushed outside of the body to engulf food -Sometimes the water vascular system is used to pry open the shells of molusks; once inside the shell, the cardiac stomach begins to swallow and digest the food. It is then brought back inside the body, where the partially digested food is sent to the pyloric stomach and then on to the intestines and excreted through the anus or the mouth.

Starfish Stomachs

Tissues and Organs Contain a complete digestive tube (tubular gut) that leads from mouth to anus Have an open and reduced circulatory system but no heart Have a simple radial nervous system with a modified nerve net, but no brain Some contain a ganglia Have gonads in various places in their bodies

Interesting Facts Sea cucumbers: http://www.youtube.com/watch?v=vsLBOkYLLeI The word echinoderm means “spiny-skinned” A starfish is one of the only animals that can turn its stomach inside out Echinoderms have no finite life expectancy and no “old age”

Sources http://www.wetwebmedia.com/echinode.htm http://animaldiversity.ummz.umich.edu/site/accounts/information/Echinodermata.html http://en.wikibooks.org/wiki/General_Biology/Animal_Evolution#Three_Germ_Layers http://www-biol.paisley.ac.uk/biomedia/text/txt_echino.htm   http://www.oceaninn.com/guides/echino.htm http://ebiomedia.com/prod/BOechinoderms.html http://en.wikipedia.org/wiki/Tube_feet http://www.dailykos.com/story/2006/10/20/201118/36 Picture http://people.hws.edu/mitchell/oz/images96/Linckia.jpg http://cache.eb.com/eb/image?id=72235&rendTypeId=35 http://www.oceaninn.com/guides/echino59.gif http://oceanexplorer.noaa.gov/explorations/03edge/logs/aug27/media/seaurchin_600.jpg