72
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
or, perhaps, even days. This opinion is indirectly supported by the
suggestion of Thorson (1946), Wilson (1958) and other investigators
that pediveligers of many bivalves are able to postpone metamorphosis
if conditions of environment are unfavorable for completion of this
important stage.
Literature contains few references to anatomical changes accompanying metamorphosis of bivalves. This is understandable because,
until recently, few forms were successfully and repeatedly grown
to this stage. Prytherch's (1934) description of metamorphosis in
C. virginiea, Cole's (1938) in 0. e d u b and, especially, Quayle's (1962)
in Venerupie pullustra should be mentioned as contributing to our
knowledge in this field. However, since a description of the major
anatomical changes occurring during metamorphosis does not constitute a part of this paper, no references will be made to the details
of this phenomenon in larvae of the mollusks studied by us.
As already mentioned, the number of days required for larvae of
the same species to reach metamorphosis depends upon a complex
combination of ecological factors, of which temperature and quantity
and quality of food are the most important. Each species, of course, has
its optimal temperature range for larval development, as well as
minimum and maximum levels within which development is possible.
Since all species that we cultured were grown to metamorphosis at
room temperatures ranging from 18" to 24OC, it is quite certain that
this part of the temperature range is comparatively favorable for
development of most bivalves of our waters, as well as some of the
exotic species with which we worked. However, information aa to
complete temperature range within which development of each of
these species is possible is still lacking in most instances.
For example, aa
already mentioned, in the case of M . mercenaria it has been ascertained
that larvae grown at 18°C began to metamorphose 16 days after
fertilization and continued to set as late as the 30th day. Thus; at thh
temperature, the period between beginning and completion of metamorphosis of larvae of the same cultures extended for 14 days. At a
temperature of 24°C the earliest metamorphosing larvae were noticed
on the 11th day, and the latest, 22 days after fertilization. At the
considerably higher temperature of 30°C setting of clam larvae began
as early as the 7th day after fertilization and was normally completed
within 5 to 7 days, or by the 14th day, although in some of the more
erratic cultures the last setting larvae were observed on the 16th day
after fertilization (Loosanoff et al., 1951).
Similar observations on larvae of C. virginicu showed that, at a
We have obtained such data for some species.
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
or, perhaps, even days. This opinion is indirectly supported by the
suggestion of Thorson (1946), Wilson (1958) and other investigators
that pediveligers of many bivalves are able to postpone metamorphosis
if conditions of environment are unfavorable for completion of this
important stage.
Literature contains few references to anatomical changes accompanying metamorphosis of bivalves. This is understandable because,
until recently, few forms were successfully and repeatedly grown
to this stage. Prytherch's (1934) description of metamorphosis in
C. virginiea, Cole's (1938) in 0. e d u b and, especially, Quayle's (1962)
in Venerupie pullustra should be mentioned as contributing to our
knowledge in this field. However, since a description of the major
anatomical changes occurring during metamorphosis does not constitute a part of this paper, no references will be made to the details
of this phenomenon in larvae of the mollusks studied by us.
As already mentioned, the number of days required for larvae of
the same species to reach metamorphosis depends upon a complex
combination of ecological factors, of which temperature and quantity
and quality of food are the most important. Each species, of course, has
its optimal temperature range for larval development, as well as
minimum and maximum levels within which development is possible.
Since all species that we cultured were grown to metamorphosis at
room temperatures ranging from 18" to 24OC, it is quite certain that
this part of the temperature range is comparatively favorable for
development of most bivalves of our waters, as well as some of the
exotic species with which we worked. However, information aa to
complete temperature range within which development of each of
these species is possible is still lacking in most instances.
For example, aa
already mentioned, in the case of M . mercenaria it has been ascertained
that larvae grown at 18°C began to metamorphose 16 days after
fertilization and continued to set as late as the 30th day. Thus; at thh
temperature, the period between beginning and completion of metamorphosis of larvae of the same cultures extended for 14 days. At a
temperature of 24°C the earliest metamorphosing larvae were noticed
on the 11th day, and the latest, 22 days after fertilization. At the
considerably higher temperature of 30°C setting of clam larvae began
as early as the 7th day after fertilization and was normally completed
within 5 to 7 days, or by the 14th day, although in some of the more
erratic cultures the last setting larvae were observed on the 16th day
after fertilization (Loosanoff et al., 1951).
Similar observations on larvae of C. virginicu showed that, at a
We have obtained such data for some species.