REARMQ OF BIVALVE MOLLUSKS
61
and oyster larvae than did equal quantities of any of these foods
separately.
D . euchlora and Dunalidla sp., both naked flagellates, as are
1. galbarn and N. lutheri, also induced better growth of oyster larvae
during the first 6 days of their development than did any of the forms
having cell walls. Thus, Davis concliidetl that, with the exception of
Prymnesium parvum, which is toxic, evm the poorest of the naked
flagellates is a better food for young Iirrvrbe of G . virginica than any of
the organisms with cell walls. This coriclusion supports the earlier
one of Cole (1939) and Bruce et al. (1940), that nanoplankton may
differ in their value as food for larvae of 0. edulis. Davis found, nevertheless, that Chlorella (580), Platymows sp., Chlorococcum sp., and
Phaeodactylum tricornutum, all forms having cell walls, were utilized
by larvae of C . virginica, but growth, particularly of younger individuals,
was slow and might have occurred because of presence in the water of
other food materials.
Observations on behavior of larvae of approximately twenty
different species of bivalves grown at our laboratory have shown that,
in general, as far as their qualitative food requirements are concerned,
they can be roughly divided into two or, perhaps, three groups. The
first group, well-represented by larvae of oysters of the genus Crassostrea, is able to utilize, during early straight-hinge stages, only a few
of the many food forms (Davis, 1953; Davis and Guillard, 1958). The
second group includes larvae of such species aa Mereenaria mercenaria
and Mytilus edulis, which seem to be able to utilize most of the microorganisms, provided that they are small (.nough to be ingested. The
third, an intermediate group, also can be tentatively recognized. This
group includes such larvae as those of larviparous oysters of the genuu
Ostrea, which are much less restricted in their qualitative food rcquirements than larvae of the genus Cruseostron, yet they are unable to
grow quite as well on some of the foods as larvae of M . mercenaria.
The food requirements of the two marginal groups were clearly
shown in our experiments where larvae of the oyster, C. virginica, and
clam, M . mercenaria, were placed simultaneously and kept together
in the same laboratory culture vessels or in large outdoor tanks. All
cultures were given the same food, which consisted of mixed phptoplankton in which small, green algae, such as Chlorella, normally predominated. Under these conditions larvae of 21.1. nlercenaria grew rapidly
and metamorphosed approximately in 12 days, while larvae of C. virginica, after attaining straight-hinge stage, showed virtually no growth
and eventually died. The results of theje early experiments were
confirmed by Davis (1953), who showed that while young larvae of
61
and oyster larvae than did equal quantities of any of these foods
separately.
D . euchlora and Dunalidla sp., both naked flagellates, as are
1. galbarn and N. lutheri, also induced better growth of oyster larvae
during the first 6 days of their development than did any of the forms
having cell walls. Thus, Davis concliidetl that, with the exception of
Prymnesium parvum, which is toxic, evm the poorest of the naked
flagellates is a better food for young Iirrvrbe of G . virginica than any of
the organisms with cell walls. This coriclusion supports the earlier
one of Cole (1939) and Bruce et al. (1940), that nanoplankton may
differ in their value as food for larvae of 0. edulis. Davis found, nevertheless, that Chlorella (580), Platymows sp., Chlorococcum sp., and
Phaeodactylum tricornutum, all forms having cell walls, were utilized
by larvae of C . virginica, but growth, particularly of younger individuals,
was slow and might have occurred because of presence in the water of
other food materials.
Observations on behavior of larvae of approximately twenty
different species of bivalves grown at our laboratory have shown that,
in general, as far as their qualitative food requirements are concerned,
they can be roughly divided into two or, perhaps, three groups. The
first group, well-represented by larvae of oysters of the genus Crassostrea, is able to utilize, during early straight-hinge stages, only a few
of the many food forms (Davis, 1953; Davis and Guillard, 1958). The
second group includes larvae of such species aa Mereenaria mercenaria
and Mytilus edulis, which seem to be able to utilize most of the microorganisms, provided that they are small (.nough to be ingested. The
third, an intermediate group, also can be tentatively recognized. This
group includes such larvae as those of larviparous oysters of the genuu
Ostrea, which are much less restricted in their qualitative food rcquirements than larvae of the genus Cruseostron, yet they are unable to
grow quite as well on some of the foods as larvae of M . mercenaria.
The food requirements of the two marginal groups were clearly
shown in our experiments where larvae of the oyster, C. virginica, and
clam, M . mercenaria, were placed simultaneously and kept together
in the same laboratory culture vessels or in large outdoor tanks. All
cultures were given the same food, which consisted of mixed phptoplankton in which small, green algae, such as Chlorella, normally predominated. Under these conditions larvae of 21.1. nlercenaria grew rapidly
and metamorphosed approximately in 12 days, while larvae of C. virginica, after attaining straight-hinge stage, showed virtually no growth
and eventually died. The results of theje early experiments were
confirmed by Davis (1953), who showed that while young larvae of