Hydra: Phylum Cnideria



The diagram below will help you locate the bud, basal disc and tentacles on this hydra

  Some information is from the red book (Animals without backbones, pg. 81)

http://en.wikipedia.org/wiki/Hydra_(genus)
http://www.madsci.org/posts/archives/2000-11/973856032.Zo.r.html

Morphology- At one end of a hydra is a adhesive foot which is called the basal disc. At the other end is the mouth and one to twelve tentacles (cnidae). Each tentacle has cnidocytes (stinging cells) which containg nematocysts that shoot out a paralysing dart like thread when a little trigger hair (cnidocil) comes in contact with prey. The hydra has two main body layers (epidermis and gastrodermis) that are separated by a gel-like substance (mesoglea). Respiration and excretion occur by diffusion in the epidermis layer.

Habitat- Unpolluted fresh water lakes, streams and ponds in temperate and rainforest areas.

Movement- The simplest movement is by gliding (ameboid movement by basal cells) yet the fastest method looks somewhat like somersaulting. The tentacles attach to the bottom (adhesive thread capsules), the base is "thrown" over, the base attachs to the bottom again, the tentacles release and this whole procedure is repeated.



A Somersaulting Hydra



On this hydra there are 6 tentactles
that help it eat and move.





Eating- The tentacles stretch out and when one comes in contact with prey it paralyses it. The tentacles wrap around the prey and slowly bring it to the mouth. Digestive enzymes are released to break down the food and then phagocytosis occurs to engulf the bits of food.