98
VICTOR L. LOOSANOW AND W
Y C. DAVIS
in larvae only about 180 p long, but often it was only a thickening
of the shell edge on the side opposite the foot. In our extensive studies
of living material and numerous preparations of larvae imbedded in
balsam, in permanent slides, we were unable to find such " deformed "
larvae as those shown by Sullivan (1948).
Early larval stages of A. simplex are very light, almost transparent in color (Fig. 32). Even larvae nearing metamorphosis remain
silvery transparent except, of course, their digestive organs which, aa
a rule, take on the color of the food that they contain. I n this respect
our observations are rather different from those of Sullivan (1948), who
stated that, at first, Anomia larvae are pale yellow but, later, become
deep yellow, except for the viscera, which are dark gray.
Since larvae of A. simplex may be mistaken for those of oysters,
especially in advanced stages when umbones in both species are quite
prominent, one way to distinguish the two species is to remember that
in A. simplex the digestive organs are situated much higher, lying
almost under the umbones.
I n the early stages of our work on cultivation of A. simplex larvae,
which was conducted in 1950 and 1951, the only food that was regularly available waa a mixture of green algae composed largely of
Chlorella. Although the larvae reached metamorphosis when fed this
food, their growth, as a rule, was slow and mortality heavy. Later,
when cultures of I. galbana and M. lutheri became available, the larvae
responded well to the new food, growing much faater and showing
lower mortality. When fed these flagellates at room temperatures,
many larvae of A. simplex began to metamorphose after the 12th day
although, in the same cultures, some larvae were still swimming
33 days after fertilization.
As already mentioned, one of the most interesting observations
made on cultures of A. simplex was what appeared to be partial metamorphosis, or metamorphosis without attachment to substratum
(Loosanoff, 1961). Partial metamorphosis was characterized by
disappearance of the velum, but retention of a functional foot. Moreover, these partially metamorphosed individuals were unable to
attach to the substratum, and their shells showed a distinct demttrcation line between larval and post-larval portions.
G. Pecten irradians Lamarck
The early embryonic development of the bay scallop, P. iwadians,
also called Aequipecten irradians, has been described by a number of
authors, including Fullarton (1890), Drew (1906), Belding (1910),
VICTOR L. LOOSANOW AND W
Y C. DAVIS
in larvae only about 180 p long, but often it was only a thickening
of the shell edge on the side opposite the foot. In our extensive studies
of living material and numerous preparations of larvae imbedded in
balsam, in permanent slides, we were unable to find such " deformed "
larvae as those shown by Sullivan (1948).
Early larval stages of A. simplex are very light, almost transparent in color (Fig. 32). Even larvae nearing metamorphosis remain
silvery transparent except, of course, their digestive organs which, aa
a rule, take on the color of the food that they contain. I n this respect
our observations are rather different from those of Sullivan (1948), who
stated that, at first, Anomia larvae are pale yellow but, later, become
deep yellow, except for the viscera, which are dark gray.
Since larvae of A. simplex may be mistaken for those of oysters,
especially in advanced stages when umbones in both species are quite
prominent, one way to distinguish the two species is to remember that
in A. simplex the digestive organs are situated much higher, lying
almost under the umbones.
I n the early stages of our work on cultivation of A. simplex larvae,
which was conducted in 1950 and 1951, the only food that was regularly available waa a mixture of green algae composed largely of
Chlorella. Although the larvae reached metamorphosis when fed this
food, their growth, as a rule, was slow and mortality heavy. Later,
when cultures of I. galbana and M. lutheri became available, the larvae
responded well to the new food, growing much faater and showing
lower mortality. When fed these flagellates at room temperatures,
many larvae of A. simplex began to metamorphose after the 12th day
although, in the same cultures, some larvae were still swimming
33 days after fertilization.
As already mentioned, one of the most interesting observations
made on cultures of A. simplex was what appeared to be partial metamorphosis, or metamorphosis without attachment to substratum
(Loosanoff, 1961). Partial metamorphosis was characterized by
disappearance of the velum, but retention of a functional foot. Moreover, these partially metamorphosed individuals were unable to
attach to the substratum, and their shells showed a distinct demttrcation line between larval and post-larval portions.
G. Pecten irradians Lamarck
The early embryonic development of the bay scallop, P. iwadians,
also called Aequipecten irradians, has been described by a number of
authors, including Fullarton (1890), Drew (1906), Belding (1910),