276 
PACIFIC SCIENCE, Vol. XV, April 1961 
gata\ they differ in the nature of the homogomph 
spiniger, the pygidium, and the presence or ab- 
sence of cilia on the parapodia. There are some 
distinct characteristics for the male of M. varie- 
gata\ it is not known whether or not sexual 
dimorphism occurs in M. eniwetokensis. The 
diagnostic characters for the known species of 
the genus are summarized in Table 1. 
TYPE MATERIAL : The holotype, one paratype, 
and two additional specimens have been de- 
posited in the U. S. National Museum. 
TYPE LOCALITY: Intertidal region on the 
lagoon side of Aaraanbiru Island, Eniwetok 
Atoll, Marshall Islands ( Fig. 1 ) . 
ECOLOGY: As stated above, pieces of coral 
rock of loose substrate were preserved in the 
field at each station visited. M. eniwetokensis 
was collected in this manner. It was associated 
with the following species of polychaetes: 
Aaraanbiru Island, lagoon side, substrate 
coral rock and beach rock with algae attached. 
Polychaetes: M. eniwetokensis (2 specimens), 
Haplosyllis spongicola Grube ( 1 ) , Opistosyllis 
longicinata Monro (6), Ceratonereis mirabilis 
Kinberg ( 17 ) , Eunice afra Peters ( 1 ) , Lysidice 
collaris Grube (3 ), Palola siciliensis Grube 
( 3 ) , Dodecaceria laddi Hartman ( 2 ) , and Poly- 
op hthalmus pictus (Dujardin) (19). 
Igurin Island, ocean side, substrate coral rock 
and fragments taken from under coral head 
near surge zone. Polychaetes: Micronereis eni- 
wetokensis (1 specimen), Eurythoe complanata 
TABLE 1 
Comparisons of the Known Species of Micronereis 
CHARACTERISTIC 
M. variegata 
M. nanaimoensis 
M. halei 
M. eniwetokensis 
Length 
2-4 mm. 
13-15 mm. 
7 mm. 
1. 5-2.0 mm. 
Number of 
setigerous segments 
$ 
$ 
17-18 
21 
23 
26 
20-25 
(sex unknown) 
17 
( sex unknown ) 
Palpi 
absent 
present 
present 
present 
Jaws 
dimorphic; 
$ 5 teeth 
2 4 teeth 
4-5 teeth 
6 teeth 
4 teeth 
Crotchets in $ , 
tnird segment 
2 curved 
5+ crested 
unknown 
unknown 
Spines on appendage 
of homogomph 
spinigers 
present 
present 
absent 
absent 
Cilia on parapodia 
absent 
present 
absent 
present 
Pygidium 
2 anal cirri 
2 anal cirri in $ 
and $ ; also 2 
lateral lobes in $ 
2 lateral lobes; 
ventral bilobed 
membrane 
Unique pigmentation 
none 
2 red bands on 
tentacular cirri; 
see original account 
for body 
pigmentation 
brown band on 
tentacular cirri 
none 
Unique characters 
none 
capillary setae in 
6 
inferior notopodial 
and 
superior neuropodial 
lobes in parapodium 
none 
Geographical 
distribution 
Europe, 
Mediterranean Sea 
British Columbia, 
Canada 
South Australia 
Eniwetok Atoll, 
Marshall Islands 
