Trachylinae (also Trachylina, Trachylinida, etc.) is a subclass of

hydrozoans Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specialize ...

. It is placed at order rank in many older classifications, and limited to contain the

Narcomedusae Narcomedusae is an order of hydrozoans in the subclass Trachylinae. Members of this order do not normally have a polyp stage. The medusa has a dome-shaped bell with thin sides. The tentacles are attached above the lobed margin of the bell with ...

Trachymedusae Trachymedusae belong to the phylum Cnidaria and the class Hydrozoa, among the 30 genera are 5 families containing around 50 species in all, the family Rhopalonematidae has the greatest diversity. Description Trachymedusae are identifiable by the ...

, the

Actinulidae Actinulida are an order of hydrozoans in the subclass 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 Narcomedus ...

, then considered an independent order, and also the

Limnomedusae Limnomedusae is an order of hydrozoans. Taxonomy The taxon was erected by Danish marine biologist Paul Lassenius Kramp in 1938 to accommodate certain families of hydrozoans with biphasic life histories. It includes genera with medusae with ect ...

which were traditionally placed in the

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

Hydroida Hydroidolina is a subclass of Hydrozoa and makes up 90% of the class. Controversy surrounds who the sister groups of Hydroidolina are, but research has shown that three orders remain consistent as direct relatives: Siphonophorae, Anthoathecata, an ...

". It is not entirely clear whether the Limnomedusae and the Trachymedusae as conventionally circumscribed are

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

The freshwater jelly ''

Craspedacusta sowerbyi ''Craspedacusta sowerbii'' or peach blossom jellyfish is a species of freshwater hydrozoan jellyfish, or hydromedusa cnidarian. Hydromedusan jellyfish differ from scyphozoan jellyfish because they have a muscular, shelf-like structure called ...

'' is a well-known member of the Limnomedusae and might thus belong here.

Development

Of the four orders:

, and

, 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 Embryonic may refer to: *Of or relating to an embryo * ''Embryonic'' (album), a 2009 studio album by the Flaming Lips *''Embryonics ''Embryonics'' is a double-CD compilation of tracks by the Australian progressive metal band, Alchemist. It w ...

and

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

stage.Osadchenko, Kraus (2018)

Footnotes

References

* (2005)
The Hydrozoa Directory

Retrieved 2008-JUL-08. *Osadchenko, B.V., Kraus, Y.A. Trachylina: The Group That Remains Enigmatic Despite 150 Years of Investigations. Russ J Dev Biol 49, 134–145 (2018). https://doi.org/10.1134/S1062360418030074 Hydrozoa Animal subclasses {{Hydrozoa-stub