Zoology 250 Lecture 9a
CTENOPHORA (comb jellies)
- 1) Odd phylum of ~100 species; all marine, most pelagic; can be key predators in mid-ocean environment (eat fish larvae & zooplankton)
- 2) 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
- c) two long, branching tentacles covered with colloblasts (unique, very adhesive cell type) extend from deep tentacle sheaths
- d) exhibit conspicuous biradial symmetry
- 3) Share three features with Cnidaria:
- a) diploblastic organization with extensive middle layer (mesoglea?)
- b) possess only a mouth (no true anus; curious anal pores)
- c) gastrovascular cavity with radiating canals
- 4) 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
- 5) Evolutionarily enigmatic; some believe related to deuterostomes
- a) middle layer exhibits tissue-like characters (muscle cells, nerve cells, mesenchyme cells)
- b) middle layer develops from mesenchyme cells similar to primary mesenchyme cells in larval echinoderms
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Copyright © 1999 by A. Richard Palmer. All rights reserved.
(revised Jan. 7, 1999)