112
VICTOR L. LOOYANOFF AND HARRY C. DAVIS
the larvae are about 140 p in length although, even then, the hinge
line may appear straight when seen from certain angles. As the larvw
grow, the umbo becomes more prominent and in older larvae it is
somewhat more pronounced than in M. mercenaria (Fig. 37).
When fed Chlorella sp. larvae reached metamorphosis in about
2 weeks. However, by giving them better food, such as naked flagellates, and by increasing the temperature of the water, setting size could
be reached several days earlier.
The smallest metamorphosed individuals with a large, functional
foot and fully resorbed velum measured about 175 p in length, or about
the same as that reported for M. mercenaria. The majority of the larvae
metamorphosed when they were between 200 and 220 p in length, but
some much larger larvae measuring about 235 p in length still possessed
a functional velum and were able to swim. Yoshida (1960) gave the
size of fully grown veligers of T . variegata as 215 x 195 p.
As in most of our larval cultures, the color of the larvae depended,
to a large extent, upon the food given. Furthermore, differences in
size among larvae of the same cultures were of about the same magnitude as in cultures of other species. It has also been definitely established
that larvae of T. semidecussata are susceptible to fungus diseases.
Because of our prolonged studies of T . semidecus~ata we have had
an opportunity to observe their adaptability to changes in their
surroundings. These clams were able to survive considerable variations
in temperature and salinity, which occur over the tidal flats of Milford
Harbor in front of our laboratory. During one winter, when the temperature of the water remained below zero for several weeks and the
shores were covered with a thick layer of ice, only about 3% of the
clams planted on the flat, near the mean low water level, died. The
clams also survived periods of freshets, such as were caused by hurricane
" Donna '' in 1960, when salinity of the water in Milford Harbor was
reduced almost to zero and remained low for several days.
The clams spawned and their larvae set normally in our experimental ponds. The small clams grew to a size of about 1 cm by the
middle of September.
N. Pitar (= Callocardia) MT~UUTUZ Godd
This small mollusk, which somewhat resembles H. mercenaria, is
found along the northern section of our Atlantic shore, roughly from
Prince Edward Island to Cape Hatteras. In some sections of this range,
in Narragansett Bay, it is quite numerous.
Recent literature contains few references to propagation or larval
VICTOR L. LOOYANOFF AND HARRY C. DAVIS
the larvae are about 140 p in length although, even then, the hinge
line may appear straight when seen from certain angles. As the larvw
grow, the umbo becomes more prominent and in older larvae it is
somewhat more pronounced than in M. mercenaria (Fig. 37).
When fed Chlorella sp. larvae reached metamorphosis in about
2 weeks. However, by giving them better food, such as naked flagellates, and by increasing the temperature of the water, setting size could
be reached several days earlier.
The smallest metamorphosed individuals with a large, functional
foot and fully resorbed velum measured about 175 p in length, or about
the same as that reported for M. mercenaria. The majority of the larvae
metamorphosed when they were between 200 and 220 p in length, but
some much larger larvae measuring about 235 p in length still possessed
a functional velum and were able to swim. Yoshida (1960) gave the
size of fully grown veligers of T . variegata as 215 x 195 p.
As in most of our larval cultures, the color of the larvae depended,
to a large extent, upon the food given. Furthermore, differences in
size among larvae of the same cultures were of about the same magnitude as in cultures of other species. It has also been definitely established
that larvae of T. semidecussata are susceptible to fungus diseases.
Because of our prolonged studies of T . semidecus~ata we have had
an opportunity to observe their adaptability to changes in their
surroundings. These clams were able to survive considerable variations
in temperature and salinity, which occur over the tidal flats of Milford
Harbor in front of our laboratory. During one winter, when the temperature of the water remained below zero for several weeks and the
shores were covered with a thick layer of ice, only about 3% of the
clams planted on the flat, near the mean low water level, died. The
clams also survived periods of freshets, such as were caused by hurricane
" Donna '' in 1960, when salinity of the water in Milford Harbor was
reduced almost to zero and remained low for several days.
The clams spawned and their larvae set normally in our experimental ponds. The small clams grew to a size of about 1 cm by the
middle of September.
N. Pitar (= Callocardia) MT~UUTUZ Godd
This small mollusk, which somewhat resembles H. mercenaria, is
found along the northern section of our Atlantic shore, roughly from
Prince Edward Island to Cape Hatteras. In some sections of this range,
in Narragansett Bay, it is quite numerous.
Recent literature contains few references to propagation or larval