Alicaligus tripartitus gen. et sp. nov., a Caligid Copepod 
found on the Gills of Sarda orient alis (T. & S.) 1 
Sueo M. Shiino 2 
The new parasitic copepod which forms 
the object of the present paper was found by 
the author on the gills of Sarda orientalis (T. 
& S.) at Owase, Mie Prefecture, Japan. It was 
rather small and its outward appearance was 
very peculiar. A closer examination revealed 
that it belongs to the suborder Caligoida and, 
according to the structure of the first and the 
last legs, ought to be classed within the family 
Caligidae. However, it cannot be referred to 
any of the hitherto known genera of this 
family, but evidently forms the type of a new 
genus, the diagnosis of which is given below. 
The parasite sticks to a host gill filament 
lengthwise, grasping it by the second max- 
illipeds and directing the tail to its free end. 
Unlike orginary caligids, the new one does 
not appear to be capable of swimming, at 
least in the mature stage. 
Alicaligus gen. nov. 
female. Cephalon and first 3 thoracic seg- 
ments fused into a strongly convex carapace, 
with its lateral parts bent ventrad as paired 
folds. Fourth segment small, without dorsal 
plates. Genital segment expanded, much 
larger than carapace. Abdomen likewise di- 
lated, 1 -segmented. Frontal plates with suck- 
ing disks. Cephalic appendages as in Caligus . 
1 Contribution No. 19 from the Faculty of Fisheries, 
Prefectural University of Mie, Tsu-City, Japan. Manu- 
script received June 18, 1954. 
2 Faculty of Fisheries, Prefectural University of Mie, 
Tsu-City, Japan. 
First maxillae and sternal furca absent, second 
maxillae close to sides of mouth tube. First 
and last pairs of legs uniramous, 3-jointed. 
Other legs biramous, with rami 3-jointed in 
second pair, but 1-jointed in third pair. En- 
dopodites of latter rudimentary. Caudal rami 
laminate. 
male. In general appearance much different 
from female, but resembling ordinary caligid 
males. Carapace flattened; neither genital seg- 
ment, nor abdomen expanded. First maxillae 
present. Otherwise as in female. 
Type species: Alicaligus tripartitus n. sp. 
Alicaligus tripartitus sp. nov. 
Figs. 1, 2 
5 females and 3 males. One of them, a 
female, has been selected as the holotype, 
others are paratypes. They are preserved in 
Mie Prefectural University. 
female. Body divisible into 3 regions, con- 
nected one with another by narrowed articula- 
tion: carapace, fourth thoracic plus genital 
segments, and abdomen. Length 3.13 mm., 
carapace 0.83 X 1.00 mm., fourth plus gen- 
ital segments 1.08 X 1.68 mm., abdomen 
1.30 X 1.52 mm., and egg strings 1.62 X 0.33 
mm. Opaque, whitish, without pigment. 
Carapace quadrilateral in dorsal view, 
strongly convex above, with lateral parts 
curved ventrad as a pair of oblong folds. 
Front somewhat prominent medially, eyes 
close to anterior end. Dorsal surface uneven, 
more or less rugose, hardly divisible into dis- 
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