Trachymedusae

Taxobox
name = Trachymedusae
regnum = Animalia
subregnum = Eumetazoa
phylum = Cnidaria
subphylum = Medusozoa
classis = Hydrozoa
subclassis = Trachylinae
ordo = Trachymedusae
ordo_authority = Haeckel, 1879
subdivision_ranks = Families
subdivision = 5, see text

Trachymedusae are an order in the cnidarian class Hydrozoa. They contain some 50 species, divided among about 30 genera and 5 families, of which the Rhopalonematidae are by far the most diverse. They only reproduce sexually as medusa, never forming polypsSchuchert (2005)] . It is not known with certainty whether the group as delimited here is indeed monophyletic.

Predominatly living in the deep open oceans, they are small medusae with hemispherical to heightened bells that have a smooth and straight margin of thick tissue with ample nematocysts. They have 4, 6, 8 or more radial canals, with 8 being most common. The gonads are borne at the radial canals or where these meet the manubrium. The statocysts are of mixed tissue from both endoderm and ectoderm. Thir cnidome can include stenoteles.

Families:
* Geryoniidae
* Halicreatidae
* Petasidae
* Ptychogastriidae
* Rhopalonematidae

Footnotes

References

* (2005): [http://www.ville-ge.ch/mhng/hydrozoa/hydrozoa-directory.htm The Hydrozoa Directory] - [http://www.ville-ge.ch/mhng/hydrozoa/trachy/trachymedusae.htm Order Trachymedusae Haeckel, 1879] . Retrieved 2008-JUL-08.