Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!elroy.jpl.nasa.gov!usc!jarthur!nntp-server.caltech.edu!behind!squirrel From: squirrel@behind.caltech.edu (Patricia M. White) Newsgroups: sci.bio Subject: JellyFish Classification Message-ID: Date: 31 May 91 02:03:05 GMT Sender: news@nntp-server.caltech.edu Distribution: sci Organization: California Institute of Technology, Pasadena Lines: 41 >This question came up in conversation recently (don't ask how): Are jellyfish >animals, or are they colonies of plants or animals, like coral or sponges? We >checked some textbooks but couldn't seem to get a satisfactory answer. What >is the definitional distinction between an animal and a colony? >Just curious. >John Walsh >U33695@UICVM.BITNET My text, _The Invertebrate World_, Barth and Broshears, Saunders College Publishing, 1982, states that most jellyfish are members of the class Scyphoza, although the famed Portugese man-of-war is in the related class Hydrozoa. These are two of the classes included in the phylum Cnidaria, commonly called coelenterata. Coelenterata are radially symmetric, which means they are rather simple organisms. They possess a gastrovascular cavity, an internal space for the digestion and distribution of nutrients, "making them far more complex than sponges." For a text like this, normally as dry as the Gobi, the authors get nearly poetic about the creatures, likening them to a flexible bottle with the cork pulled. In answer to your question, the medusae, which are the jellyfish, are the sexually reproductive form in the life cycle of the organisms. Most of the time they are polyps, which are stationary and frequently colonial. Polyps expand (it's hard to say reproduce) in an asexual fashion. These two forms, polyps and jellyfish, seem very different, but they are the same animal in different life stages. Remember that there are about 8900 species in the phylum, and so there are many variations on this scheme. Some very large colonies are supposed to contain both medusae and polyps. I'm not a taxonomist, but it seems to me that a colony is a group of organisms that can survive if you disassociate them into their respective parts, whereas an animal dies if you dissect it. Pat, squirrel@above.cs.caltech.edu