296
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
in shape of recurved hook ; four swimming legs resemble those of female
except for setal armature ; endopodites of legs bear long terminal setae ;
second and third legs similar ; fifth leg as erect lobe with three terminal
setae and one on outer margin; sixth leg as flat rounded lobe with
two setae, located on posterior area of ventral surface of sixth thoracic
somite.
Humes’ ( 195413) table comparing the distinguishing characteristics
of the three species of Mytilicola found in commercially important
molluscs is reproduced in Table XVI.
Although the various stages in the life cycle of M .
porrecta have not been found, the nauplius, metanauplius, and most
probably the first copepodid stages undoubtedly are free-swimming as
they are in the two related species. Parasitization of the molluscs
most probably occurs when first copepodids invade these hosts.
Ecology. According to Humes (1954b), the pelecypods in which M .
porrecta are found occur in water with a salinity of 25 %, , . Modiolus
demissus granosissimus is the most frequently infected (42 yo) followed
by Brachidontes recurvus (18%). Only one Mercenaria mercenaria was
examined and it was infected. Humes also has noted that 400 Crassostrea virginica were examined from the area but none was parasitized.
This suggested that perhaps as in the case of M . intestinalis, the
invasive first copepodid stage is selective for certain pelecypods. The
largest number of M . porrecta in a single Modiolus was fifteen (five
males and ten females) but the average number was 2.75.
Pathology. Although pathological changes in pelecypods harboring
M . porrecta have not been studied, the fact that both M . intestinalis
and M . orientalis are known to cause injury suggests that this species
may also be injurious.
4. Panaietis haliotis Yamaguti, 1936. (Figs. 194 and 195)
Life cycle.
(Order Cyclopoida ; family Clausidiidae)
Panaietis haliotis was described by Yamaguti (1936) based on one
male and three females found in the mouth cavity of the abalone
Hccliotis (Sulculus) gigantea from “ the Pacific coast ” of Japan.
Description. Adult female (Fig. 194) with elongate body, 7.4-7-6 mm
long, tapering posteriorly ; head broadened posteriorly, 0.92-0.98 mm
long x 1-6-1.7 mm broad a t posterior end, with nearly truncate
frontal margin 0.62-0.7 mm broad ; five thoracic segments distinct,
with rounded sides, gradually narrowed posteriorly, 2.8-3.0 mm long
in combined length ; genital segment 0-5-0.6 mm long x 1.2-1.8 mm
broad, with prominent sides ; egg strings 2-25-2.7 mm long x 0.4-0.5
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
in shape of recurved hook ; four swimming legs resemble those of female
except for setal armature ; endopodites of legs bear long terminal setae ;
second and third legs similar ; fifth leg as erect lobe with three terminal
setae and one on outer margin; sixth leg as flat rounded lobe with
two setae, located on posterior area of ventral surface of sixth thoracic
somite.
Humes’ ( 195413) table comparing the distinguishing characteristics
of the three species of Mytilicola found in commercially important
molluscs is reproduced in Table XVI.
Although the various stages in the life cycle of M .
porrecta have not been found, the nauplius, metanauplius, and most
probably the first copepodid stages undoubtedly are free-swimming as
they are in the two related species. Parasitization of the molluscs
most probably occurs when first copepodids invade these hosts.
Ecology. According to Humes (1954b), the pelecypods in which M .
porrecta are found occur in water with a salinity of 25 %, , . Modiolus
demissus granosissimus is the most frequently infected (42 yo) followed
by Brachidontes recurvus (18%). Only one Mercenaria mercenaria was
examined and it was infected. Humes also has noted that 400 Crassostrea virginica were examined from the area but none was parasitized.
This suggested that perhaps as in the case of M . intestinalis, the
invasive first copepodid stage is selective for certain pelecypods. The
largest number of M . porrecta in a single Modiolus was fifteen (five
males and ten females) but the average number was 2.75.
Pathology. Although pathological changes in pelecypods harboring
M . porrecta have not been studied, the fact that both M . intestinalis
and M . orientalis are known to cause injury suggests that this species
may also be injurious.
4. Panaietis haliotis Yamaguti, 1936. (Figs. 194 and 195)
Life cycle.
(Order Cyclopoida ; family Clausidiidae)
Panaietis haliotis was described by Yamaguti (1936) based on one
male and three females found in the mouth cavity of the abalone
Hccliotis (Sulculus) gigantea from “ the Pacific coast ” of Japan.
Description. Adult female (Fig. 194) with elongate body, 7.4-7-6 mm
long, tapering posteriorly ; head broadened posteriorly, 0.92-0.98 mm
long x 1-6-1.7 mm broad a t posterior end, with nearly truncate
frontal margin 0.62-0.7 mm broad ; five thoracic segments distinct,
with rounded sides, gradually narrowed posteriorly, 2.8-3.0 mm long
in combined length ; genital segment 0-5-0.6 mm long x 1.2-1.8 mm
broad, with prominent sides ; egg strings 2-25-2.7 mm long x 0.4-0.5