of ChloreZEn, and kept at room temperature began to set about 14 days
after fertilization. Probably if given twttc:r foods, such as I. galbanu
and M. lutheri, which at the time of rearing P . morrhuanu were not
available at our laboratory, a better rate of survival and growth could
have been achieved.
Many cultures suffered mass mortality, which usually occurred
during the late stages of larval growth. These mortalities were probably
caused by the same fungi that were later found responsible for heavy
mortalities of larvae in ciiltures of M. mercenaria and several other
species.
0 . Petricola pholadiformis Lamarck
Even though the range of this clam extends from Prince Edward
Island to the West Indies and Texas and their larvae should be common
in plankton samples during the reproductive period, Sullivan (1948)
seems to be the only author who has desvribed them. According to
this author the first larvae of P. p?wladiformis normally appear in the
waters of Malpequo Bay, Prince Edward Island, about the 2nd week
of July and, after reaching peak numbers in early August, disappear
from plankton in early September.
In our laboratory, groups of P . pholcrdiformia were conditioned
for spawning from the middle of December until summer. I n the early
winter these efforts were not as successful as later in the season and
conditioning required a much longer time. For example, clams placed
in conditioning trays a t about 20°C in December required 4 to 6 weeks
before the majority responded to stimulation and spawned. In the
middle of April, however, only a week of vonditioning a t about 20°C
was sufficient, to bring these clams to spawiling condition.
Conditioned clams were induced to spawn by our usual method,
consisting of subjecting them to a quick increase in the water temperature from about 20" to 27°C and by the addition of a sperm suspension.
Later in the season spawning, especially of males. could be induced on
some occasions a t a temperature as low as 15°C. Raising the water
temperature to about 32°C always affected dams unfavorably.
Early in the season aevcral hours at the increased temperature
were often required before the first individiials, usually males, would
resp'md, whereas late in March and in A i d spawning was usually
provoked within tho first hour. Even young clams, leas than 1 yr old,
and individuals with partially damaged shellr responded to stimulation
and discharged large quantities of spawn. Often the same individual
would spawn for a while, cease spawning and then resume it. Many
individually-marked clams spawned several times during the Reason.
9
after fertilization. Probably if given twttc:r foods, such as I. galbanu
and M. lutheri, which at the time of rearing P . morrhuanu were not
available at our laboratory, a better rate of survival and growth could
have been achieved.
Many cultures suffered mass mortality, which usually occurred
during the late stages of larval growth. These mortalities were probably
caused by the same fungi that were later found responsible for heavy
mortalities of larvae in ciiltures of M. mercenaria and several other
species.
0 . Petricola pholadiformis Lamarck
Even though the range of this clam extends from Prince Edward
Island to the West Indies and Texas and their larvae should be common
in plankton samples during the reproductive period, Sullivan (1948)
seems to be the only author who has desvribed them. According to
this author the first larvae of P. p?wladiformis normally appear in the
waters of Malpequo Bay, Prince Edward Island, about the 2nd week
of July and, after reaching peak numbers in early August, disappear
from plankton in early September.
In our laboratory, groups of P . pholcrdiformia were conditioned
for spawning from the middle of December until summer. I n the early
winter these efforts were not as successful as later in the season and
conditioning required a much longer time. For example, clams placed
in conditioning trays a t about 20°C in December required 4 to 6 weeks
before the majority responded to stimulation and spawned. In the
middle of April, however, only a week of vonditioning a t about 20°C
was sufficient, to bring these clams to spawiling condition.
Conditioned clams were induced to spawn by our usual method,
consisting of subjecting them to a quick increase in the water temperature from about 20" to 27°C and by the addition of a sperm suspension.
Later in the season spawning, especially of males. could be induced on
some occasions a t a temperature as low as 15°C. Raising the water
temperature to about 32°C always affected dams unfavorably.
Early in the season aevcral hours at the increased temperature
were often required before the first individiials, usually males, would
resp'md, whereas late in March and in A i d spawning was usually
provoked within tho first hour. Even young clams, leas than 1 yr old,
and individuals with partially damaged shellr responded to stimulation
and discharged large quantities of spawn. Often the same individual
would spawn for a while, cease spawning and then resume it. Many
individually-marked clams spawned several times during the Reason.
9