Tetraplatia — Hand 
333 
mesogleal septum separating the oral coelen- 
teric pouch from the aboral (Carlgren, 1909) 
or that the passageway may be blocked by an 
endodermal plug (Dantan, 1925), although 
neither of these structures is necessarily 
present. 
There are four gonads in the tetraplatians, 
each with an oral and an aboral bilobed por- 
tion. The gonads originate below the velum in 
the axes of the buttresses and project inside the 
animal, largely filling the coelenteron when 
the animal is mature. The sexes are separate. 
In summary, the tetraplatians are consid- 
ered to be tentacleless medusans whose body 
is divisible into aboral and oral halves, sep- 
arated by a line of tissue lying in the bottom 
of a constriction, this tissue representing the 
margin of the bell and the velum. The sub- 
umbrellar part of the animal is highly reduced 
and consists of only the manubrium and the 
tissues on the adoral surfaces of the lappets. 
REVIEW OF RECORDED KNOWLEDGE 
Tetraplatia volitans was first described by 
Busch (1851), presumably from a single spec- 
imen, taken at Malaga, Spain, in the Medi- 
terranean Sea. He apparently observed the 
animal alive for a period of 2 days, and al- 
though he did not express an opinion on the 
nature or affinities of the animal, his descrip- 
tion was good enough to enable subsequent 
authors to recognize it. Shortly after Busch’s 
discovery, Krohn (1853) reported the finding 
of four specimens at Messina, Sicily. Twelve 
years later, having obtained no more spec- 
imens, Krohn (1865) published detailed ob- 
servations on the four specimens he had 
obtained and suggested they must be young 
forms of some medusa (scyphozoan). Leuck- 
art (1866), in considering the work of Krohn, 
suggested that Tetraplatia might be related 
to the medusan group of aeginids (now nar- 
comedusans), and subsequently Claus (1878) 
in a very fine study established quite definitely 
the hydromedusan nature of the animal al- 
though at the same time he seemed to feel 
that it was half medusan and half polypoidal 
and thus intermediate between polyps and 
medusae. Claus, however, used the name Te- 
trapteron ( Tetraplatia ) volitans for this species, 
and thereby created the first of the two rec- 
ognized synonyms of Tetraplatia volitans , the 
second being that of Fewkes (1883) who used 
the name Tetraptera volitans . Haeckel (1879) 
in his ’'System der Medusen” suggested Te- 
traplatia might be a larval narcomedusan or 
that it might be intermediate between the 
hydroid polyps and the craspedote medusae. 
Fewkes (1883) in a brief note suggested that 
this curious animal might be best assigned a 
position between the craspedote medusae and 
the ctenophores. Viguier (1890), in an elab- 
orate study of Tetraplatia , discussed the sim- 
ilarities of this animal to the trachymedusans, 
hydromedusans, larval actinians, scyphome- 
dusans and ctenophores and seems to favor 
their relationship to the trachyline medusae. 
Perhaps the most careful and complete study 
of the tetraplatians is that of Carlgren (1909) 
based upon specimens from the Deutsche 
Tiefsee Expedition and also on specimens 
from Messina. From a single specimen from 
the west coast of Africa he described the 
species T. chuni, and after elaborate morpho- 
logical and histological study of it and of 
specimens of T. volitans , Carlgren proposed 
a new order, the Pteromedusae, for Tetra- 
platia. This order represented a third group 
of trachyline medusae of equal rank to the 
Trachymedusae and Narcomedusae. Subse- 
quent to Carlgren’s study Krumbach (1924) 
decided that the tetraplatians were really larval 
animals in spite of their possession of well 
developed gonads, and placed them among 
the Scyphomedusae. In 1925 Dantan pub- 
lished a detailed study of Tetraplatia volitans . 
He disagreed with Carlgren’s study on a 
number of points, perhaps the most impor- 
tant of which concerned the origin of the 
statocysts. Dantan maintained that these bal- 
ance organs were of ectodermal origin, as 
opposed to the endodermal origin proposed 
by Carlgren, and after much discussion placed 
Tetraplatia among the Anthomedusae. Weill 
