Echinoderms+(Alex+Walker)


 * Phylum**: Echinodermata


 * Subkingdom**: Eumetazoa
 * Phylum**: Echinodermata
 * Classes**: Asteroidea (Starfish), Ophiuroidea (Brittle Stars), Echinoidea (Sea Urchins), Crinoidea (Feather Stars), Holothuroidea (Sea Cucumbers)




 * Body Plan**: Echinoderm larvae initially exhibit bilateral symmetry and eventually grow to exhibit radial symmetry as adults. Echinoderms possess a brittle external skeleton which is composed primarily of calcium and can feature defense mechanisms such as spines. This group of animals also utilizes a water vascular system, unique to Echinoderms, which functions in gas exchange, feeding and movement through the use of tubes filled with fluid.


 * Germ Layers**: Triploblastic (endoderm, mesoderm and ectoderm).


 * Symmetry**: Most Echinoderms exhibit radial symmetry, in which specific units of the body are arranged around a central disc. Others, such as the Sea Cucumber, exhibit bilateral symmetry.


 * Coelomate**: Echinoderms are enterocoelous coelomates, meaning that the coelom forms from pouches which have been separated from the digestive tract.


 * Habitat**: Echinoderms can be found throughout the ocean and more commonly on the sea floor. Although the organisms are often benthic, some can swim for great lengths of time and can even attach themselves to other marine animals.


 * Movement**: Some Echinoderms move through the use of "tube feet". These tube feet consist of fluid-filled sac which can extend out through the external skeleton and push off along the ground. Other organisms in the phylum move through attaching themselves to other organisms.
 * Skeletal System**: External skeleton composed of calcium.


 * Evolutionary Advancement**: Many believe that echinoderms originated from sessile organisms with bilateral symmetry. Some believe that locomotion and radial symmetry allowed echinoderms to attach to other organisms and gain greater access to nutrients. There remains an extensive fossil record of echinoderms because their skeleton is composed of calcium carbonate.


 * Special Adaptations**: Echinoderms are particularly known for their ability to regenerate lost limbs. In some cases, the entire body can be regenerated from a single limb so long as that limb contains part of the nervous system of the animal. This allows some organisms to reproduce asexually by separating themselves into two parts.


 * Feeding Patterns**: Echinoderms are either passive filter-feeders (Brittle Stars) or detritivores (Sea Stars). They possess a simple digestive system which consists of a mouth, stomach and anus. The mouth is often found on the underside of the animal and the anus is typically located facing upwards.


 * Respiration**: Echinoderms have a relatively primitive method of respiration which uses tube feet and simple gill systems for contact with the surrounding water. This allows for a direct exchange of carbon dioxide and oxygen.


 * Circulation**: Echinoderms do not possess a true heart yet due to their radial symmetry, blood flows from the center of the organism to the surrounding limbs by way of the water vascular system.

Organisms possess no specialized excretory organs and ammonia gas, the most common form of waste, is removed from the body through diffusion.
 * Excretory**:


 * Nervous System**: Echinoderms do not have brains and rely upon nerves located along each limb. In addition, some possess eye spots which are only capable of sensing light.

Echinoderms are separated into male and female organisms, yet certain organisms can reproduce both sexually and asexually. During sexual reproduction, millions of eggs are deposited on the sea floor where they can be fertilized by spermatozoa. In asexual reproduction, echinoderms are capable of of separating themselves into two parts and then regenerating lost limbs.
 * Reproduction**:

http://www.lowbird.com/data/images/2011/06/starfish.jpg http://www.seasky.org/wallpaper/assets/wallpaper_sea/brittle-star-1024.jpg http://images.nationalgeographic.com/wpf/media-live/photos/000/179/cache/sea-urchins08-sea-urchin_17935_600x450.jpg http://www.alaska-in-pictures.com/data/media/1/feather-star-pattern_6081.jpg http://www.starfish.ch/Fotos/echinoderms-Stachelhauter/seacucumbers-Seewalzen/Bohadschia-argus1.jpg http://www.sfdj.com/learn/13.jpg http://universe-review.ca/I10-82-starfish.jpg http://www.mesa.edu.au/echinoderms/images/class.jpg
 * Pictures URLs**:

http://www.mesa.edu.au/friends/seashores/echinoderms.html http://www.bumblebee.org/invertebrates/ECHINODERMATA.htm http://www.nhc.ed.ac.uk/index.php?page=24.25.312.320 http://www.mesa.edu.au/echinoderms/default.asp http://www.oceaninn.com/the-nature-preserve/echinoderms/
 * Bibliography**: