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 Ctenophora - comb jellies
This phylum's 'place'
relative to other phyla:
  • Metazoan
    • Diploblast?
Classes within this taxon:

Ctenophores are gelataneous marine animals, typically planktonic.
100-150 species but diversity is likely significant higher (Why?)

    General Characteristics



Why might radial symmetry work well for a planktonic organism?


Natural History

Why light up?

Class of ctenophores

Class Tentaculata presence of two tentacles

Includes VenusíGirdle

  Mythologic tree

and a parasitic form living in the body of the pelagic Thaliacean Salp. 

Class Nuda no tentacles

Includes the species Beroe, roughly thimble shaped and opens up like a sack to engulf their prey.


The phylogenetic relationship of ctenophores to other phyla

Not well preserved as fossils (why?), Recently, two species have been found from the Late Devonian, and are quite similar to living ctenophores. Other ctenophore-like forms have been found in the Cambrian-age Burgess Shale and Chengjiang Formation.

Despite similarities to cnidarians, ctenophores appear more closely related to the bilaterian animals:

However, some molecular data has contradicted this view.  Perhaps (also suggested by gross morphological similarities):

or even:

More recent molecular data suggest that ctenophores may be the first phylum to split off from the lineage that gave rise to all other animals, including sponges!  Development of the nervous system seems to be radically different, supporting this idea.

Ideas to consider from the ctenophores:

Intermediate characteristics do not necessarily imply intermediate ancestry. How else could these intermediate characteristics be explained?  Should we necessarily always think of each phylum as a modification of a previous phylum so that all phyla can be lined up from most primitive to most advanced?


What might a phylogenetic tree of the four basal phyla look like based on morphology?
Lecture Sources:
  • Pechenik. Jan A.  2000. Biology of the Invertebrates.  McGraw-Hill, New York.

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