9. T H E CLASS CRUSTACEA
301
Description. Adult female (Fig. 198) with fairly transparent body
of uniform grayish or pinkish color ; total length 1-1-1.3 mm ; metasome
cylindrical ; head fused with first segment and about as wide as long ;
second, third, and fourth segments slightly tapered, fifth segment
abruptly reduced to half the width of the fourth segment, but about
the same length ; urosome as long as metasome, tapered posteriorly ;
caudal rami a little longer than anal segment, six times as long as
wide; first antenna of six segments of which second segment is the
longest ; second antenna of four segments the terminal one of which is
tipped with two stout curved claws and three long, nearly straight
setae ; labrum ending in an acute, backwardly directed spine ; labium
with apparently movable terminal claw with hemispherical pad at
base beset with recurved bristles ; second maxilla of two joints with one
bristle midway on its posterior edge ; maxilliped absent ( 2 ) ; first four
swimming legs with both rami of three podomeres, distal margin of
basipodite of second leg and outer margins of both rami of first leg
fringed with stout triangular spines ; fifth leg of two segments with the
distal segment three times as long as wide and with long apical and
two stout outer serrate spines and a stalked filiform seta on dorsal
surface near tip.
Adult male much larger than female, 1.75-1-9 mm in total length ;
of same general shape as female; genital segment swollen and with
fringe of spines and single seta on each lateral margin; antennae,
mouth parts, and swimming legs as in female except that a pair of
two-jointed maxillipeds is present ; maxilliped with second segment
swollen and armed with two rows of tubercles and two setae on inner
surface, sickle-shaped apical claw, enlarged a t base where thereis a small
bristle, and serrated on inner margin.
Other informahon. Although this copepod is undoubtedly usually
found in the mantle cavity, on one occasion I found a single female in
the stomach of a specimen of M y a arenaria collected in Narragansett
Bay, Rhode Island.
M. S. Wilson (1950) has reduced Myicola spinosa, described by
Pearse (1947) from the gills and mantle of Tagelus gibbus, Dosinia
discus and Mercenaria mercenaria from Beaufort, North Carolina, to
synonymy with M . major.
7 . Other Clausidiids
I n addition to the clausidiids given above, Humes and Cressey (1958)
have described five additional species from the mantle cavities of marine
pelecypods from West Africa. Since these molluscs are presently of
301
Description. Adult female (Fig. 198) with fairly transparent body
of uniform grayish or pinkish color ; total length 1-1-1.3 mm ; metasome
cylindrical ; head fused with first segment and about as wide as long ;
second, third, and fourth segments slightly tapered, fifth segment
abruptly reduced to half the width of the fourth segment, but about
the same length ; urosome as long as metasome, tapered posteriorly ;
caudal rami a little longer than anal segment, six times as long as
wide; first antenna of six segments of which second segment is the
longest ; second antenna of four segments the terminal one of which is
tipped with two stout curved claws and three long, nearly straight
setae ; labrum ending in an acute, backwardly directed spine ; labium
with apparently movable terminal claw with hemispherical pad at
base beset with recurved bristles ; second maxilla of two joints with one
bristle midway on its posterior edge ; maxilliped absent ( 2 ) ; first four
swimming legs with both rami of three podomeres, distal margin of
basipodite of second leg and outer margins of both rami of first leg
fringed with stout triangular spines ; fifth leg of two segments with the
distal segment three times as long as wide and with long apical and
two stout outer serrate spines and a stalked filiform seta on dorsal
surface near tip.
Adult male much larger than female, 1.75-1-9 mm in total length ;
of same general shape as female; genital segment swollen and with
fringe of spines and single seta on each lateral margin; antennae,
mouth parts, and swimming legs as in female except that a pair of
two-jointed maxillipeds is present ; maxilliped with second segment
swollen and armed with two rows of tubercles and two setae on inner
surface, sickle-shaped apical claw, enlarged a t base where thereis a small
bristle, and serrated on inner margin.
Other informahon. Although this copepod is undoubtedly usually
found in the mantle cavity, on one occasion I found a single female in
the stomach of a specimen of M y a arenaria collected in Narragansett
Bay, Rhode Island.
M. S. Wilson (1950) has reduced Myicola spinosa, described by
Pearse (1947) from the gills and mantle of Tagelus gibbus, Dosinia
discus and Mercenaria mercenaria from Beaufort, North Carolina, to
synonymy with M . major.
7 . Other Clausidiids
I n addition to the clausidiids given above, Humes and Cressey (1958)
have described five additional species from the mantle cavities of marine
pelecypods from West Africa. Since these molluscs are presently of