9. THE CLASS CRUSTACEA
309
upward, in the gill-tubes, which would appear to argue an entry while still
in the nauplius-stage, through the inhalant siphon and the water-pores of
the gill-plates.
Ecology. According to Wright, female copepods found in clams
during June carry egg sacs enclosing eggs a t various stages of development, but by August they have lost their egg sacs.
Males have been reported to be much faster swimmers than females
when teased out of their hosts.
Pathology. The only information available on the effects of M .
metisiensis on its host is that reported by Wright who has stated :
No considerable irritation appears to be set up by the presence ofthe parasite
in the gill-tubes. The claws of the posterior antennae and the setae of the
various appendages are often invested by a yellowish film undoubtedly
derived from the blood of the host, but no greater exudation resulting in the
formation of a cyst round the foreign body is to be observed. . . . The granular
contents of the intestine of the copepod have a bluish-green tint, which is
most readily noticed in the wider rectum, but I must leave undecided
whether these are derived from the blood of the host.
12. Pseudomyicola ostreae Yamaguti, 1936. (Pig. 207) RADGL~FF~
Pseudomyicola ostreae, the genotype, was described by Yamaguti
(1936) based on two female specimens recovered from the branchial
cavity of Ostrea denselamellosa cultured a t the Hutami oyster bed in
Hy6go Prefecture, Japan. I n following Humes and Cressey (1958), I
am assigning it to the family Pseudomyicolidae.
Description. Female (Fig. 207) 2.1-2-43 mm long, uniformly grayish
in alcohol-preserved specimens ; head 0.45-0.51 mm x 0.525-0.625 mm,
abruptly narrowed anteriorly, with setae on each side as in first thoracic
segment ; head indistinctly demarcated from thorax ; thorax 0.9-1.25
mm long, with first four segments almost uniformly broad, 0.67 mm in
maximum breadth; fifth thoracic segment about half as long as and
much narrower than fourth but slightly broader than genital segment ;
genital segment 0.225-0.260 mm x 0.28 mm, with two transverse
rows of spines and scattered setae on ventral surface ; egg strings not
seen; abdomen of three segments, first segment 0.12-0.13 mm x 0.20.21 mm, with about ten setae on ventral side near posterior margin,
second segment 0.10-0.11 mm x 0-175 mm, third segment 0.0880.1 mm x 0.14-0.15 mm, with numerous small spines on ventral and
outer sides near posterior end; caudal rami narrow, 0.16-0.18 mm x
0.035-0.04 mm, each with two spines on outer margin, three a t tip and
(Order Cyclopoida; family Pseudomyicolidae)
309
upward, in the gill-tubes, which would appear to argue an entry while still
in the nauplius-stage, through the inhalant siphon and the water-pores of
the gill-plates.
Ecology. According to Wright, female copepods found in clams
during June carry egg sacs enclosing eggs a t various stages of development, but by August they have lost their egg sacs.
Males have been reported to be much faster swimmers than females
when teased out of their hosts.
Pathology. The only information available on the effects of M .
metisiensis on its host is that reported by Wright who has stated :
No considerable irritation appears to be set up by the presence ofthe parasite
in the gill-tubes. The claws of the posterior antennae and the setae of the
various appendages are often invested by a yellowish film undoubtedly
derived from the blood of the host, but no greater exudation resulting in the
formation of a cyst round the foreign body is to be observed. . . . The granular
contents of the intestine of the copepod have a bluish-green tint, which is
most readily noticed in the wider rectum, but I must leave undecided
whether these are derived from the blood of the host.
12. Pseudomyicola ostreae Yamaguti, 1936. (Pig. 207) RADGL~FF~
Pseudomyicola ostreae, the genotype, was described by Yamaguti
(1936) based on two female specimens recovered from the branchial
cavity of Ostrea denselamellosa cultured a t the Hutami oyster bed in
Hy6go Prefecture, Japan. I n following Humes and Cressey (1958), I
am assigning it to the family Pseudomyicolidae.
Description. Female (Fig. 207) 2.1-2-43 mm long, uniformly grayish
in alcohol-preserved specimens ; head 0.45-0.51 mm x 0.525-0.625 mm,
abruptly narrowed anteriorly, with setae on each side as in first thoracic
segment ; head indistinctly demarcated from thorax ; thorax 0.9-1.25
mm long, with first four segments almost uniformly broad, 0.67 mm in
maximum breadth; fifth thoracic segment about half as long as and
much narrower than fourth but slightly broader than genital segment ;
genital segment 0.225-0.260 mm x 0.28 mm, with two transverse
rows of spines and scattered setae on ventral surface ; egg strings not
seen; abdomen of three segments, first segment 0.12-0.13 mm x 0.20.21 mm, with about ten setae on ventral side near posterior margin,
second segment 0.10-0.11 mm x 0-175 mm, third segment 0.0880.1 mm x 0.14-0.15 mm, with numerous small spines on ventral and
outer sides near posterior end; caudal rami narrow, 0.16-0.18 mm x
0.035-0.04 mm, each with two spines on outer margin, three a t tip and
(Order Cyclopoida; family Pseudomyicolidae)