130
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Leloup ; Cole (a) ; Meyer and Mann ; Havinga ; Dollfus) dealt with the
ecology, host mortalities, distribution, and morphology of the parasite.
Unfortunately, detailed histopathological findings were apparently not
available a t that time and as far as I can determine are still unavailable.
Mori (1935) has described a second species, Mytilicola orientalis, in
the gut of Crassostrea gigas from the Inland Sea of Japan. He has stated
that the same parasite also occurs in Mytilus crassitesta in the same
region. Wilson ( 1938) apparently overlooked Mori’s description since
he has described representatives of Mori’s copepod as Mytilicola ostreae
from Crassostrea gigas in Puget Sound, Washington. These oysters
had been introduced to Puget Sound from Japan. Basing his interpretation on the older definition of a parasite, that is, one which inflicts
injury to its host, Wilson did not consider Mytilicola orientalis as a
parasite since, in his opinion, it does not harm the host and its mouthparts are not suited for sucking blood or biting tissues. He did point
out, however, that this copepod maintains its position within the
oyster’s gut by holding on with the distal segments of the second
antennae which are provided with two spine-like setae and terminate
in a stout curved claw. Humes) (1958a) belief that M . orientalis is a
true parasite is shared by me. The fact that this copepod is consistently
and frequently found in the gut of oysters and other pelecypods suggest
some type of obligatory metabolic dependency. Certainly the structure
of their second antennae suggests adaptation to symbiosis, most
probably parasitism. Furthermore, Odlaug ( 1946), who studied the
physiological state of Ostrea lurida infected with Mytilicola orientalis,
has found that such oysters display a subnormal physiological condition
(lower Condition Index), thus indicating a metabolic drain on the host.
It should be noted that Odlaug has found that this copepod is more
numerous in Mytilus edulis than in Ostrea lurida and has concluded that
the mussel is the normal host, thus again suggesting some degree of
obligatory relationship. Similarly Rankin (personal communication)
has studied the effects of Mytilicola orientalis on Ostrea lurida. He has
found that if more than five copepods parasitize one oyster, the host
becomes weak and watery, and if twelve or more copepods are present,
death generally ensues. In one instance he noted erosion of the host’s
gut wall caused by ingestion by the copepod. This is the k s t , although
limited, observation of histopathology.
Sparks (1962) has contributed a study of Mytilicola orientaliscaused histopathology in Crassostrea gigas in the State of Washington.
He has reported that during light and initial infections the ciliated
columnar gut epithelium remains unaltered ; however, if large numbers
MARINE MOLLUSCS AS HOSTS FOR SYMBIOSES
Leloup ; Cole (a) ; Meyer and Mann ; Havinga ; Dollfus) dealt with the
ecology, host mortalities, distribution, and morphology of the parasite.
Unfortunately, detailed histopathological findings were apparently not
available a t that time and as far as I can determine are still unavailable.
Mori (1935) has described a second species, Mytilicola orientalis, in
the gut of Crassostrea gigas from the Inland Sea of Japan. He has stated
that the same parasite also occurs in Mytilus crassitesta in the same
region. Wilson ( 1938) apparently overlooked Mori’s description since
he has described representatives of Mori’s copepod as Mytilicola ostreae
from Crassostrea gigas in Puget Sound, Washington. These oysters
had been introduced to Puget Sound from Japan. Basing his interpretation on the older definition of a parasite, that is, one which inflicts
injury to its host, Wilson did not consider Mytilicola orientalis as a
parasite since, in his opinion, it does not harm the host and its mouthparts are not suited for sucking blood or biting tissues. He did point
out, however, that this copepod maintains its position within the
oyster’s gut by holding on with the distal segments of the second
antennae which are provided with two spine-like setae and terminate
in a stout curved claw. Humes) (1958a) belief that M . orientalis is a
true parasite is shared by me. The fact that this copepod is consistently
and frequently found in the gut of oysters and other pelecypods suggest
some type of obligatory metabolic dependency. Certainly the structure
of their second antennae suggests adaptation to symbiosis, most
probably parasitism. Furthermore, Odlaug ( 1946), who studied the
physiological state of Ostrea lurida infected with Mytilicola orientalis,
has found that such oysters display a subnormal physiological condition
(lower Condition Index), thus indicating a metabolic drain on the host.
It should be noted that Odlaug has found that this copepod is more
numerous in Mytilus edulis than in Ostrea lurida and has concluded that
the mussel is the normal host, thus again suggesting some degree of
obligatory relationship. Similarly Rankin (personal communication)
has studied the effects of Mytilicola orientalis on Ostrea lurida. He has
found that if more than five copepods parasitize one oyster, the host
becomes weak and watery, and if twelve or more copepods are present,
death generally ensues. In one instance he noted erosion of the host’s
gut wall caused by ingestion by the copepod. This is the k s t , although
limited, observation of histopathology.
Sparks (1962) has contributed a study of Mytilicola orientaliscaused histopathology in Crassostrea gigas in the State of Washington.
He has reported that during light and initial infections the ciliated
columnar gut epithelium remains unaltered ; however, if large numbers