66 
PACIFIC SCIENCE, Vol. VIII, January, 1954 
curious phenomenon concerning the distribu- 
tion of Prohoscidactyla is the extremely wide 
range of the species, P. ornata. Kramp (1952) 
lists this species from the Pacific coast of 
Mexico, Japan, the tropical Pacific, the Ma- 
layan Archipelago, and from Madras, India, 
and, further, from the Atlantic coast of North 
America, the Bahamas, Brazil, and Fernando 
Po on the west coast of Africa. The other 
species have much more localized distribu- 
tions. Maas (1905) has pointed out that the 
habit of budding practically puts Prohoscidac- 
tyla in a class with holoplanktonic organisms. 
Actually, the habit of budding does not seem 
to be a character of the genus but rather of 
the subspecies of P. ornata which, indeed, 
may well account for its curious and wide- 
spread distribution. 
At this time it would appear that the follow- 
ing species exist, occupying in general the 
following areas. Most of the literature relevant 
to these distributions has already been cited, 
and that which has been omitted can be found 
in Mayer (1910) or Browne and Kramp (1939). 
1 . P. flavicirrata 
2. P. circumsabella 
3. P. Occident alls 
4. P. stellata 
5. P. ornata ornata 
6. P. ornata gemmifera 
7. P. ornata stolonifera 
8. P. mutabilis 
North Pacific 
Central Californian Pacific 
Southern Californian Pacific 
European North Atlantic 
Atlantic, New England to 
North Carolina 
East and West Tropical 
Atlantic 
East and West Tropical 
Pacific to Indian Ocean 
South Atlantic and Straits 
of Magellan 
The above species may be related and may 
have evolved along the following lines, but, 
of course, this is speculative. To begin with, 
I suggest a northern, inherently variable me- 
dusa such as P. flavicirrata which possibly as 
a circumpolar species gave rise to the Atlantic 
P. stellata. P. flavicirrata or its predecessor 
also gave rise to P. circumsabella and to P. 
ornata. P. ornata seems to have developed its 
southern subspecies gemmifera in the Atlantic 
which by spanning the Panamanian Isthmus 
has given rise to the subspecies stolonifera 
which has spread via the tropical current sys- 
tems throughout the tropical Pacific. P. oc- 
cidentalis may be the offshoot of P. ornata 
stolonifera or of P. circumsabella or some other 
species. The origin of P. mutabilis of the 
Falkland Islands and perhaps of the Pacific 
is not apparent. However, another pattern of 
evolution can be suggested which, based upon 
major existing ocean currents, seems even 
more plausible. Thus, starting with the vari- 
able P. mutabilis and utilizing the currents of 
the South Atlantic Ocean, medusae could be 
carried to the Isthmus of Panama, to the 
Gulf Stream, and into the North Atlantic to 
England. The Pacific species could be de- 
rived from a crossing at Panama or by moving 
directly into the Pacific from the circumpolar 
Antarctic currents. It would be possible to 
start at almost any point in the oceans and 
arrive at the same end results. 
It is, of course, not necessary to accept any 
point or species as the origin of this group 
of medusae; the important fact would seem 
to be that today Prohoscidactyla is a genus 
which occurs in most oceans and presumably 
has spread to these oceans via ocean currents 
acting upon the planktonic medusoid phase 
of its life history. One factor which would 
appear to limit the distribution of this genus 
in its spread would be a lack of suitable hoses. 
Therefore, if this group and its evolution are 
to be understood adequately, further studies 
are needed not only on the hydroids and 
medusae but also on the sabellids to whose 
fate Prohoscidactyla has apparently attached 
its own hopes for the future. 
REFERENCES 
Berkeley, E., and C. Berkeley. 1952. Part 
9, Annelida, 9b (2) Polychaeta Sedentaria. 
Canadian Pacific Fauna. 139 pp. University 
of Toronto Press, Toronto. 
Bigelow, H. B. 1909. The Medusae. Harvard 
Univ., Mus. Comp. ZooL, Mem. 37: 1-243, 
48 pis. 
Brandt, J. T. 1834. Prodromus descriptionis 
animalium ab H. Mertensio in orbis ter- 
