Trachylinae

Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of hydrozoans. It is placed at order rank in many older classifications, and limited to contain the Narcomedusae, Trachymedusae, the Actinulidae, then considered an independent order, and also the Limnomedusae which were traditionally placed in the paraphyletic "Hydroida". It is not entirely clear whether the Limnomedusae and the Trachymedusae as conventionally circumscribed are monophyletic^[1]

Trachylinae
Crossota sp.
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Hydrozoa
Subclass:	Trachylinae Haeckel, 1879
Orders
Actinulida Swedmark & Teissier, 1958 Limnomedusae Kramp, 1938 Narcomedusae Haeckel, 1879 Trachymedusae Haeckel, 1866
Synonyms
Automedusae Trachylida Trachylidae Trachylina Trachylinida

The freshwater jelly Craspedacusta sowerbyi is a well-known member of the Limnomedusae and might thus belong here.

Development

Of the four orders: Narcomedusae, Trachymedusae, Actinulidae, and Limnomedusae, only Limnomedusae has any sort of polyp stage, and even then it is very tiny(less than 1mm) with no tentacles. This is uncommon for other jellyfish under the phylum cnidaria. These jellyfish also tend to have fewer cells during their embryonic and larvae stage.^[2]