124
VICTOR L. LOOSANOFF AND HARRY 0. DAVIS
soft shell clam as 62.5 p, while Battle (1932) gave the egg size as varying
from 70 to 8 0 p . Our measurements of hundreds of eggs discharged
by different females and on different occasions showed that the majority
were between 68 and 73 p in diameter, with a modal size of 70-5 p.
Beldirig (193 1) expressed the opinion that artificial cultivation of
M . arenuria is virtually impossible because the eggs either fail to
develop normally or else never pass the young veliger stage. Nevertheless, Belding was able to show that, unlike other pelecypods, eggs
stripped from M . arenaria can be artificially fertilized.
The smallest normal straight-hinge larvae recorded in our cultures
measured only about 86 x 71 p. These were, however, extremely
uncommon and normal, fully-formed straight-hinge larvae were
usually about 93 x 77 p. As in most pelecypod larvae, they were light
in color at this stagc and their internal organs were not well defined.
They remained quite light, almost transparent, until a length of about
110 p was reached. As the larvae grew, they became darker. Nevertheless, as mentioned on several occasions, these larvae do not possess
characteristic colors that would help to distinguish them from members
of other genera or species of bivalves. In our experiments, where
larvae of this species were fed different foods, their color ranged from
a dark reddish-brown to dark green. We cannot, therefore, agree
with Sullivan (1948) that brown pigmentation in large larvae of M.
arenaria is diagnoRtic of that species.
In older larvae measuring about 175p and longer we noticed the
presence, in the margins of the mantle, of irregular opaque spots
varying in size from 5 to 15p. These granules occurred with such
regularity that we are inclined to consider them a8 aharackristic of
thc speciali, at kaHt during Irttf. I&rvti t Ht&gc:H. .jwrgf.rinf:n ( I fr/tfj) flot,ic4i
a somewhat different pigmcntatiori of the soft parts of larvae of
M . nrertarici mtmuring ahout 200 p i d larger. He also suggested that
thiR may 1)c a reliablc specific character.
'Thc size of larvae of M . arennria at setting is extremely varied.
Metamorphosis may occur at any lerigth from 170 to 228 p. The latter
is the size of the largest free-swimming larva ever recorded in our
cultures. The majority metamorphosed at a length between 200 and
The smallest larva in which the foot was present waH about 166 p
long but many of the larvae had a well-developed foot by the time they
reached 175p in length. The presence of a large foot doeR not necessarily indicate that the velum ha8 already hccome non-fiinctional.
Larvae as long as 210 p have hcen w:m at timcH nwimmirlg rttmit cuing
both the velum, which still nppc:ared to ht: of ncJrrrirrI ~ i m ,
arid t l h
210 p.
VICTOR L. LOOSANOFF AND HARRY 0. DAVIS
soft shell clam as 62.5 p, while Battle (1932) gave the egg size as varying
from 70 to 8 0 p . Our measurements of hundreds of eggs discharged
by different females and on different occasions showed that the majority
were between 68 and 73 p in diameter, with a modal size of 70-5 p.
Beldirig (193 1) expressed the opinion that artificial cultivation of
M . arenuria is virtually impossible because the eggs either fail to
develop normally or else never pass the young veliger stage. Nevertheless, Belding was able to show that, unlike other pelecypods, eggs
stripped from M . arenaria can be artificially fertilized.
The smallest normal straight-hinge larvae recorded in our cultures
measured only about 86 x 71 p. These were, however, extremely
uncommon and normal, fully-formed straight-hinge larvae were
usually about 93 x 77 p. As in most pelecypod larvae, they were light
in color at this stagc and their internal organs were not well defined.
They remained quite light, almost transparent, until a length of about
110 p was reached. As the larvae grew, they became darker. Nevertheless, as mentioned on several occasions, these larvae do not possess
characteristic colors that would help to distinguish them from members
of other genera or species of bivalves. In our experiments, where
larvae of this species were fed different foods, their color ranged from
a dark reddish-brown to dark green. We cannot, therefore, agree
with Sullivan (1948) that brown pigmentation in large larvae of M.
arenaria is diagnoRtic of that species.
In older larvae measuring about 175p and longer we noticed the
presence, in the margins of the mantle, of irregular opaque spots
varying in size from 5 to 15p. These granules occurred with such
regularity that we are inclined to consider them a8 aharackristic of
thc speciali, at kaHt during Irttf. I&rvti t Ht&gc:H. .jwrgf.rinf:n ( I fr/tfj) flot,ic4i
a somewhat different pigmcntatiori of the soft parts of larvae of
M . nrertarici mtmuring ahout 200 p i d larger. He also suggested that
thiR may 1)c a reliablc specific character.
'Thc size of larvae of M . arennria at setting is extremely varied.
Metamorphosis may occur at any lerigth from 170 to 228 p. The latter
is the size of the largest free-swimming larva ever recorded in our
cultures. The majority metamorphosed at a length between 200 and
The smallest larva in which the foot was present waH about 166 p
long but many of the larvae had a well-developed foot by the time they
reached 175p in length. The presence of a large foot doeR not necessarily indicate that the velum ha8 already hccome non-fiinctional.
Larvae as long as 210 p have hcen w:m at timcH nwimmirlg rttmit cuing
both the velum, which still nppc:ared to ht: of ncJrrrirrI ~ i m ,
arid t l h
210 p.