880 
THE VOYAGE OF H.M.S. CHALLENGER. 
a special subgenus ; they all present considerable differences from the shallow- water 
species, but these appear to be due to modifications produced by some unknown causes 
which affect the inhabitants of the deep sea, and not to be a mark of near affinity ; for 
example, the epimera of Serolis bromleyana, Serolis near a, and to a less degree of 
Serolis gracilis, are enormously elongated, and terminate in sharp spine-like points ; 
this, however, is not necessarily an indication 
of near affinity, because the same thing is met 
with in other deep-sea Isopoda ; moreover, 
Serolis necera, in the disposition of the spines 
and carinse of the caudal shield, most nearly 
resembles Serolis schythei among the shallow- 
water species, while Serolis bromleyana is unlike 
this or any other shallow-water species that has 
been yet described. Serolis antarctica is con- 
spicuous for the extensive sculpturing of the 
dorsal surface of the body, and eyes are quite 
absent — a condition obviously correlated with 
the great depth at which it exists ; in the other 
species the eyes are large but whitish in colour 
from the partial or entire absence of pigment, 
as in many deep-sea fishes, Pycnogonids and 
Crustacea. 
“ The large size of Serolis necera and Serolis 
bromleyana is all the more remarkable since it 
does not appear to be a general rule that the 
deep-sea Isopoda are conspicuously larger than 
their shallow-water allies, though there are certain exceptions, such as Bathynomus 
giganteus of Milne-Edwards, which is no less than 9 inches in length. , 
“ Nearly all the families of the Isopoda are represented by deep-sea forms, but in very 
different proportions ; the most characteristic are the Munnopsidse and the Arcturidse, 
and of both these a great number of new species were obtained during the voyage. The 
Munnopsidse are indeed typical inhabitants of the deep sea, as has been already made 
known by the results of Professor Sars’ dredgings off the coast of Norway; very few of the 
forms described by him were got in water shallower than 120 fathoms, and the majority 
range beyond the 300 fathom limit. The Munnopsidse collected by the Challenger 
were invariably dredged in very deep water, one species having been obtained from 
2600 fathoms. At Station 68, in 2175 fathoms, a very remarkable example of the 
Munnopsidse was dredged ; this specimen is of considerable size, upwards of an inch in 
length (the majority of the group do not exceed half an inch or so), and the integument. 
Fig. 025. — Serolis bromleyana , Sulim. Antarctic 
Ocean, 1975 fatlioms. 
