• 1) An odd phylum of ~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 extend from deep tentacle sheaths and are covered with colloblasts (unique, very adhesive cell type)
  • 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!

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