134 
PACIFIC SCIENCE, VoL XIV, April I960 
Marutea commensal with Heterocentrotus 
mammillatus. 
Coutiere, 1905. Fauna and Geog. Mal- 
dive and Laccadive Archipelagoes 2(4): 868. 
[Comparison with A. dorsalis.'] 
Nobili, 1907. Mem. R. Accad. Torino 
II, 57: 353; 5 specimens from Marutea, one 
from Fakarawa, one from Rikitea, French 
Oceania. [Remarks on commensalism.} 
Arete indicus Coutiere, 1905. Fauna and Geog. 
Maidive and Laccadive Archipelagoes 2(4): 
863, figs. 134, 135; one specimen from Mal- 
dive Archipelago, numerous specimens from 
Djibouti and 1 from Central America. [See 
A. dorsalis indicus Coutiere above.} 
Nobili, 1906. Bull. Sci. Fr. Belg. 20: 
24; 1 specimen from the Persian Gulf. [Par- 
tial redescription.} 
Balss, 1915. Ergebn. Zool. 30: 21; 
specimens from the Red Sea. [Locality only.} 
Coutiere, 1921. Trans. Linn. Soc. Lond. 
17(4): 413; specimens from the Indian 
Ocean. [Locality only.} 
Arete iphianassa de Man, 1910. Tijdschr. Ned. 
Dierk. Ver. II, 11 (5) : 312; 2 specimens from 
Indonesia. 
de Man, 1911. Siboga Exped. 39a 1 (2) : 
16, pis. 3, 4, figs. 11-lle. [Same as the above 
with figures.} 
de Man, 1922. Siboga Exped. 39a 4 (5) : 
22, pi. Ill, figs. 11-1 If; 1 specimen from 
Indonesia. [Redescription.} 
Banner, 1956. Pacif. Sci. 10(3): 324; 
6 examples from the Marianas Islands. [Lo- 
cality only.} 
Arete maruteensis Coutiere var. salibabuensis 
de Man, 1910. Tijdschr. Ned. Dierk. Ver. II, 
11(5): 313; 1 female from Salibabu Island, 
Indonesia. 
de Man, 1911. Siboga Exped. 39a 1 (2) : 
169, fig. 13 a-c. [Same specimens as the 
above, with plates.} 
Arete amboinensis de Man, 1910. Arch, Natur- 
gesch. 76(1): 25, figs. 1-6; 1 example from 
Amboina. 
Arete intermedins Yu, 1931. Bull. Mus. Hist. 
Nat., Paris 3(6): 513, fig. 1; one specimen 
from Amoy, China. 
Arete ghardaqensis Ramadan, 1936. Bull. Fac. 
Sci. Egypt. Univ. 6: 15, pi. 1, fig. 208; 5 
specimens from the Red Sea. 
Athanas AND Arete 
According to Couriered monograph (1899: 
322 et seq.) the principal differences between 
Athanas and Arete lie in the carpus of the 
second legs, five-jointed in Athanas and four- 
jointed in Arete; in the biunguiculation of the 
dactylus of the third leg in Arete, simple in 
Athanas; and in the branchial formula, which 
contains only six epipodites in Arete and seven 
in Athanas. The other differences he cited were 
mostly differences in proportion, not form. 
("Antennules et antennes & Athanas, mais mas- 
sives et courtes.”) With his description of 
Athanas areteformis Coutiere felt he had a speci- 
men that showed transition between the two 
genera. Subsequent description of species by 
various authors extended the knowledge of dif- 
ferences in form within the two genera, espe- 
cially in Athanas, which, for example, was found 
to include species with a biunguiculate dactylus. 
The two genera have continued to be ac- 
cepted as separate in spite of the fact that 
Athanas areteformis on one hand and Arete bor- 
radailei and, later, Arete ghardaqensis, on the 
other hand, lie in a position somewhat inter- 
mediate between the two genera. They were still 
separated on the basis of the carpus of the 
second legs and on the branchial formula. 
This is in spite of the fact that in other genera 
it has been recognized that the branchial for- 
mula varies within a genus, for example in 
Betaeus and Alpheopsis, and that the number of 
carpal articles of the second legs may also vary 
as in Alpheopsis and Synalpheus. Kemp (1915: 
295 ) in his description of At h anus polymorphus 
reported that in his specimens the number of 
carpal articles varied from four to five. 
In the present study, the branchial formula 
of Athanas djiboutensis was examined in 17 
specimens from one locality on Canton Island, 
Phoenix group. Because the species is small and 
the branchial formula is difficult to discern, most 
specimens were examined on both sides. Only 
two of the specimens had mastigobranchs on the 
third thoracic appendages and the setobranchs 
on the fourth, the branchial formula for the 
genus; on the other 15 specimens the last masti- 
