''Tetraplatia'' is a genus of hydrozoans in the order

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 ...

. It is the sole genus in the monotypic

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Tetraplatidae.

Taxonomy and systematics

Since their discovery in the 1850s, there has been disagreement over the

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

of the tetraplatids. Some authorities considered that they were aberrant

hydrozoa 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 specializ ...

ns while others thought that they were unusual scyphozoans,

cubozoa Box jellyfish (class Cubozoa) are cnidarian invertebrates distinguished by their box-like (i.e. cube-shaped) body. Some species of box jellyfish produce potent venom delivered by contact with their tentacles. Stings from some species, including ...

ns or

staurozoa Staurozoa is a class of Medusozoa, jellyfishes and hydrozoans. It has one extant order: Stauromedusae (stalked jellyfishes) with a total of 50 known species. A fossil group called Conulariida has been proposed as a second order, although this is ...

ns. Examination of the

ribosomal DNA Ribosomal DNA (rDNA) is a DNA sequence that codes for ribosomal RNA. These sequences regulate transcription initiation and amplification, and contain both transcribed and non-transcribed spacer segments. In the human genome there are 5 chromos ...

has shown that they are hydrozoans in the order

. The genus seems to be of recent origin.

Genera and species

The World Register of Marine Species lists the following taxa in the family Tetraplatidae: *Genus ''Tetraplatia'' Busch, 1851 **''Tetraplatia chuni'' Carlgren, 1909 **''Tetraplatia volitans'' Busch, 1851

Characteristics

Unlike the other members of the order, members of the family Tetraplatidae have no tentacles nor bell but are worm-like in shape. The body is divided by a transverse groove beside which there are four muscular flaps or lappets used for swimming. Each of these contains two sense organs. In one species there are four flying buttresses alternating with the lappets. The gonads are epidermal and have lobes either side of the groove.

''Tetraplatia chuni''

''Tetraplatia chuni'' is similar in shape and size to ''T. volitans'' but lacks the flying buttresses connecting the two ends. It seems to be a much rarer species as only a few specimens have been recorded. These have all been found in the southern Atlantic Ocean.

''Tetraplatia volitans''

''Tetraplatia volitans'' has s spindle shaped body 4-9mm long with a transverse groove nearer the aboral end. Four flying buttresses arch over this groove and connect the oral and aboral ends. It has four longitudinal rows of nematocysts with four shorter rows in between. There are eight pairs of lappets with sense organs between. The species has a cosmopolitan distribution, being found worldwide from the surface down to a depth of about 900 meters. It feeds on small

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

.''Tetraplatia volitans'' Busch, 1851
Retrieved 2011-11-07.

References

Narcomedusae {{hydrozoa-stub