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PACIFIC SCIENCE, Vol. IX, July, 1955 
actinulae are in general planuloid, tentacled 
organisms; the tentacles arising at the place 
on the circumference which demarks the 
aboral, ex-umbrellar, area from the oral, manu- 
brial area. In the actinula in its simplest form 
there is no sub-umbrellar region, but as it 
grows into a medusa the bell margin grows 
outward and downward, thus creating the 
sub-umbrellar space. Tetraplatia in form and 
adult structure strongly suggests its actinular 
affinities and except for the absence of ten- 
tacles seems to be a compromise between 
the structure of actinula larvae and adult 
trachyline medusae. 
There is very little information to guide us 
to a decision as to what position Tetraplatia 
should have among the Narcomedusae. May- 
er (1910) reviewed the several possible classi- 
fications within this group, and recognized 
only two families, the Solmaridae and Aegini- 
dae; the Solmaridae are without stomach 
pouches while the Aeginidae possess them. 
Unfortunately Mayer did not consider Tetra- 
platia at any point in his work. Of these two 
families of Narcomedusae, Tetraplatia , by its 
possession of a pouched stomach, seems to 
most closely approach the Aeginidae and 
within this family it would best be placed 
within the sub-family Cunanthinae. 
Within the Cunanthinae can be placed such 
genera as Cunantha , Hydroctena , Cunoctantha , 
and Cunina . Of these genera Tetraplatia would 
seem to be most closely related to Cunantha , 
although Mayer (1910, Vol. 2, p. 449) said, 
"... the 'genus’ Cunantha is, I believe, only 
a developmental stage of Aegina.” Cunantha 
is, however, clearly a medusan and does not 
grossly suggest Tetraplatia by its form, but its 
special features do suggest some of the special 
features of Tetraplatia . For example, the ex- 
umbrella bears rows of nematocysts as in 
Tetraplatia and moreover Cunantha has only 
four broad lappets. The stomach pouches of 
Cunantha are very small and only four in 
number, again as in Tetraplatia. The tentacles 
of Cunantha are rudimentary whereas there are 
none in Tetraplatia. If Cunantha exists as a 
valid genus might not this last character in- 
dicate a trend toward loss of tentacles? How- 
ever, the medusoid form, sensory clubs, 
numerous statoliths, otoporpae, and gonad 
ring of Cunantha all represent characters quite 
different from those of Tetraplatia. 
Broch (1929) in reviewing the classification 
of the Narcomedusae recognizes three fami- 
lies, the Cuninidae, Aeginidae and Solmari- 
dae. Of the three, again, Tetraplatia best fits 
the definition of the aeginids but at the same 
time cannot be clearly identified as an aeginid 
or indeed even as a narcomedusan if one 
considers its structure and particularly its 
possession of a statocyst. 
Dantan (1925) did not believe that the 
statocyst of Tetraplatia could be considered 
as derived from the endoderm. Indeed, the 
whole statocyst is not, nor is it in other 
trachylines, although the internal cells of the 
lithostyle are. In Tetraplatia it seems to be 
fairly obvious that the lithostyles, or at least 
the lithocytes, are endodermal. This character 
then clearly places Tetraplatia among the 
trachylines. Dantan (1925, p. 452) although 
disagreeing entirely with Carlgren’s classifica- 
tion of Tetraplatia , tried to conserve Carlgren’s 
name, Pteromedusae, by making it a family 
of the Anthomedusae. This was a kind gesture 
on Dantan’s part; however, it is an action 
contrary to the International Rules of Zoo- 
logical Nomenclature under which the only 
allowable family name would have to be 
Tetraplatiidae if Tetraplatia is the type genus. 
If Tetraplatia is to be placed among the 
Narcomedusae it will stand out as a very 
aberrant, highly divergent, form. Its posses- 
sion of an enclosed lithostyle is a trachy- 
medusan character and the definition of the 
Narcomedusae would therefore have to be 
modified to meet this situation. That Tetra- 
platia has strong narcomedusan characters 
certainly is not to be denied; however, it is 
an animal that seems to have evolved along a 
path quite distinct from the normal narco- 
medusan line. One can hypothesize that 
Tetraplatia is the result of retrogressive evolu- 
