146 
The proportions of the chelipeds are given in 
Table 3. The 2.7 mm. female from Tahiti with 
the asymmetrical chela (Fig. 3 n) is almost cer- 
tain to belong to this species, for it was col- 
lected with larger specimens of the species with 
normal chelae. There may be some question 
about the 3.0 mm. female from Eniwetok (Fig. 
3 o) for it was collected alone and its rostrum 
had been broken. However, as its chelae could 
represent an earlier stage of development, as it 
agrees with the species on other characteristics, 
and as it was collected from the typical habitat 
of this species, we believe we can safely assume 
it to belong to A. rhothionastes. The develop- 
ment of ischial spines of the chelipeds appears 
to be variable. 
If these two smallest specimens given in the 
table do belong to this species, then here again 
we have the variation on the chelipeds with age 
and sex that seems to be characteristic of so 
many species of this genus. The degree of uni- 
formity in the rostrum and corneal spines casts 
some doubt upon the uniting of species like 
A. naifaroensis and A. areteformis (see previous 
sections ) . 
A. rhothionastes is closely related, morpho- 
logically, to two species, A. lamellifer Kubo and 
A. marshallensis Chace. This group of species 
of the Dimorphus group are characterized by 
the lack of supracorneal teeth, acute extracorneal 
teeth, rounded infracorneal teeth, with the palm 
definitely longer than the carpus in mature 
females, and with simple dactyli of the third 
legs. The distinction between this species and 
A. lamellifer is fine and questionable, for the 
chief differences lie in the length of the rostrum, 
which exceeds the length of the antennular 
peduncle in A. lamellifer and usually reaches 
only to the end of the second antennular article 
in A. rhothionastes, and in the armature of the 
fingers of the large chela of the male, bearing 
merely setae in Kubo’s species and bearing heavy 
teeth and setae in this species. The ischium of 
the cheliped of A. rhothionastes appears con- 
sistently longer than that reported by Kubo. The 
carpus of the cheliped is consistently longer in 
A. marshallensis than in A. rhothionastes in the 
immature stages and in the fully developed 
females; there are no obvious differences be- 
tween the males of the two species. 
PACIFIC SCIENCE, Vol. XIV, April I960 
Possibly better than the morphological dif- 
ferentiation between the three species would be 
the ecological differences. A. rhothionastes so far 
as had been collected always occurs in regions of 
surge or heavy surf on coral reefs, usually on the 
outermost reef fronts in the coralline ridge and 
near the end of the surge channels; A. lamellifer 
has been reported only from the colder waters 
of Tokyo Bay (Tiba Prefecture of Kubo is now 
transliterated Chika) under stones on a muddy 
shore, and while there was nothing in the orig- 
inal listing for A. marshallensis that would in- 
dicate ecology, all specimens I have collected 
from Eniwetok, the type locality, came from 
under rocks on a sandy bottom in a somewhat 
protected cove on the lagoon side of one of the 
islets. 
The specific name is derived from the Greek 
rhothion, meaning breakers or surf, and nastes, 
meaning inhabitant. 
Athanas esakii Kubo 
Athanas esakii Kubo, 1940^. J. Fish. Inst. Tokyo 
34(1): 93-95, fig. 13 a-p. 
DISCUSSION: This small and obviously im- 
mature specimen was collected with numerous 
and larger specimens of A. marshallensis Chace 
apparently in a single ecological niche. On the 
basis of ecology, therefore, the separation of the 
two species is doubtful. 
The specimen appears to be distinct from 
A. marshallensis only in the presence of an acute 
infracorneal tooth, all traces of which are lack- 
ing in A. marshallensis . While this characteristic 
does not appear to be reliable in other species 
of this genus, as in A. areteformis, the lack of 
intergrading specimens would make the place- 
ment of A. marshallensis in synonymy at this 
time a questionable step. 
The chelae of this specimen are not exactly 
like either A. marshallensis nor A. esakii , but 
sufficiently close to both that the differences 
could easily be the result of immaturity. In this 
specimen the chelae have the following pro- 
portions: 
Merus Carpus Palm Fingers 
Smaller chela 1.5 1.0 1.0 0.6 
Larger chela 1.3 0.8 1.0 0.5 
