120
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
many other larvae, even those nearing metamorphosis, did not display
it. Sullivan (1948) did not mention the presence of an " eye '' in E.
directus larvae and Werner (1939), working with a species that he
called Cultellus pellucidus, a form closely related to En&, stated that
its larvae do not possess " eyes ". This observation is quite important
because, according to Rees (1960), the description by Werner of
C. pellucidas was really that of Ensis. Our observation that the
"eye "-like structure is sometimes present in larvae of E. directw
and Werner's, that it is always absent in the species that he studied,
may indicate that Reed assumption is not correct and that the
C. pellucidus of Werner was not an Ensis.
One of the characteristics of larvae of E. directus which may be of
diagnostic value is the presence of a clear area around the edge of the
shell. This area, which does not occur in larvae of other speciea tihat
we have studied, is well defined and clearly seen. It appeared in larvae
of about 120 p long and persisted until they reached a length of 180
to 190 p . Later this area became less definite and more or less merged
with other parts of the shell. Near setting, however, a purple wst
became apparent along the edge of the larval shell.
In rearing of E. directus the presence of many abnormal larvae
was quite common, not only in cultures that were started from stripped
eggs, but also in those that were grown from normally discharged o m .
In several cultures, usually those where larvae were approwhing
setting stage, mortalities on an epizootic scale were recorded. In
several instances practically all of the larvae died within a short period,
usually less than one day. Since this happened before we learned the
devastating effect of larval diseases caused by fungi or bacteria, we
did not establish the cause of death of these larvae but strongly suspect
that these mortalities were principally the result of fungus infestations.
Q. dlactra (= Spisula) 80&h3ima Dillwgn
The clams used in these studies were taken from the sandy beclchee
of the south shore of Long Island, New York. They were shipped to
Milford and kept for many months, either in the laboratory or in the
harbor, without any appreciable mortality, although the salinity at
Milford is about 27 ppt, or approximately 8 ppt lower than in the
areas where the clams were dredged. The clams survived equally
well whether they were allowed to dig into sand or were kept in wire
baskets containing no soil. To prevent mortality, however, it was
necessary to expel bubbles of air which were trapped inside the clams
while they were out of water. Clams placed on their sides cannot expel
these bubbles and, eventually, die.
VICTOR L. LOOSANOFF AND HARRY C. DAVIS
many other larvae, even those nearing metamorphosis, did not display
it. Sullivan (1948) did not mention the presence of an " eye '' in E.
directus larvae and Werner (1939), working with a species that he
called Cultellus pellucidus, a form closely related to En&, stated that
its larvae do not possess " eyes ". This observation is quite important
because, according to Rees (1960), the description by Werner of
C. pellucidas was really that of Ensis. Our observation that the
"eye "-like structure is sometimes present in larvae of E. directw
and Werner's, that it is always absent in the species that he studied,
may indicate that Reed assumption is not correct and that the
C. pellucidus of Werner was not an Ensis.
One of the characteristics of larvae of E. directus which may be of
diagnostic value is the presence of a clear area around the edge of the
shell. This area, which does not occur in larvae of other speciea tihat
we have studied, is well defined and clearly seen. It appeared in larvae
of about 120 p long and persisted until they reached a length of 180
to 190 p . Later this area became less definite and more or less merged
with other parts of the shell. Near setting, however, a purple wst
became apparent along the edge of the larval shell.
In rearing of E. directus the presence of many abnormal larvae
was quite common, not only in cultures that were started from stripped
eggs, but also in those that were grown from normally discharged o m .
In several cultures, usually those where larvae were approwhing
setting stage, mortalities on an epizootic scale were recorded. In
several instances practically all of the larvae died within a short period,
usually less than one day. Since this happened before we learned the
devastating effect of larval diseases caused by fungi or bacteria, we
did not establish the cause of death of these larvae but strongly suspect
that these mortalities were principally the result of fungus infestations.
Q. dlactra (= Spisula) 80&h3ima Dillwgn
The clams used in these studies were taken from the sandy beclchee
of the south shore of Long Island, New York. They were shipped to
Milford and kept for many months, either in the laboratory or in the
harbor, without any appreciable mortality, although the salinity at
Milford is about 27 ppt, or approximately 8 ppt lower than in the
areas where the clams were dredged. The clams survived equally
well whether they were allowed to dig into sand or were kept in wire
baskets containing no soil. To prevent mortality, however, it was
necessary to expel bubbles of air which were trapped inside the clams
while they were out of water. Clams placed on their sides cannot expel
these bubbles and, eventually, die.