Previous Home Next 
- 1) An odd phylum of appr. 100 species; all marine, most pelagic; common members of the "gelatinous zooplankton"; they can be significant predators in mid-ocean environment (eat fish larvae & zooplankton)
- 2) Share 3 features with Cnidaria which they resemble superficially:
- a) diploblastic organization with extensive, mostly non-cellular middle layer (mesoglea?)
- b) possess only a mouth (no true anus; curious anal pores)
- c) gastrovascular cavity with radiating canals
- 3) Exhibit some curious differences from Cnidaria:
- a) asexual reproduction not well-developed
- b) all are hermaphroditic
- c) highly determinate, bi-radial cleavage
- d) lack cnidocytes
- 4) Three distinctive features:
- a) possess eight vertical "comb rows"; combs are formed from paddle-like groups of cilia
- b) comb cilia are the largest cilia known in Metazoa; ctenophores are the largest animals still able to swim using cilia
- c) two long, branching tentacles covered with colloblasts (unique, very adhesive cell type) extend from deep tentacle sheaths
- d) exhibit conspicuous biradial symmetry
- 5) Evolutionarily enigmatic; some believe related to deuterostomes
- a) middle layer exhibits some tissue-like characters (muscle cells, nerve cells, mesenchyme cells); may not be true "mesoglea"
- b) middle layer develops from mesenchyme cells similar to primary mesenchyme cells in larval echinoderms
- c) stay tuned!
Back to Zool 250 Home Page
Copyright © 2002 by A. Richard Palmer. All rights reserved.
(revised Feb. 3, 2002)
