Z250 - Lec10 Outline. Ctenophora (2005)

Zoology 250 (2005)

Phylum CTENOPHORA:
(comb jellies)

(Ctenophora study images;
click on tree to see full cladogram)

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1) An odd phylum of approx. 100 species; all marine, most pelagic; common members of the "gelatinous zooplankton"
- a) they can be significant predators in mid-ocean environment (eat fish larvae and zooplankton; e.g., Mnemiopsis invasion of Caspian Sea)
- b) can be up to 10cm in body length with 70cm tentacles
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) Four distinctive features:
- a) possess eight vertical "comb rows"; combs are formed from paddle-like groups of cilia; combs are iridescent in bright light
- 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) wide variety of body forms (gooseberry most common, also lobate or ribbon-like; some benthic forms resemble flatworms)
- d) stay tuned!

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