REARING OF BNALVE MOLLUSKS
83
The majority of larvae of C. virginica metamorphoses between 275
and 315 p in length, but occasionally free-swimming larvae may be
365 p long. Larvae were grown to metamorphosis at temperatures
ranging from about 17" to 33°C ; at the latter temperature some larvae
metamorphosed in about 12 days. Naked flagellates, such as I. galbana
and M . luthpri, are the best foods, whereas some of the green algae
with thick cell walls, such as certain Chlorelh species, are not readily
utilized by early veligers, especially at comparatively low temperaturea.
Stafford (1912), in his paper on recognition of bivalve larvae in
plankton collections, offered a description and drawings of larvae of
C. virginica of different stages. His description and, especially, the
length-width relationships of the larvae are widely different from ours.
For example, Stafford gives the following length-width (depth)
measurements, in micron8, as typical for oyster larvae: 82-8 x 69.0;
193.2 ; 310.5 x 276.0 ; and 345.0 x 303.6. A comparison with our data
shows that the majority of the above length-width ratios cannot
apply to larvae of C. virginica. For example, we found that among the
130 of our larvae measuring 110 p in length the width varied only from
105 to 125 p. I n other words, none of these larvae were only 96-6 p
wide, as indicated by Stafford. His discrepancies in length-width
ratio are even greater when he gives measurements of larger larvae.
Finally, his larvae always measure more in length than in width
(depth) although, as has already been mentioned, when a length of
about 125 p is reached, the width of the larvae begins to exceed the
length by about 5 to 1 0 p arid contiIiuwi t20 do 80 until metamorphorri8.
Siillivari'fi ( I ! b t H ) ~ n ( ~ ~ ~ ~ i i l ' ( ~ i i i t r i i t ~
t~lrict I ~ t i o ( . ~ ) t i ) i r r o ~ ~ ~ ~ ~ t ~ R
(if' Iiirvrw of
( '. viq/ii/iui JWI- I ~ I I I ~
t * ~L(~II.ILII*.
'l'hie color of larvae varies somewhat with the food, but healthy
larvae are usually a golden brown, particularly in the area of the
digestive diverticulum. Young larvae are usually pinkish-orange en
masse, but this color changes to brown and, later, to almost black as
the larvae grow larger..
Larvae are highly active and remain in suspension throughout the
free-swimming period. Large larvae, 200 p or more in length, have a.
tendency to gather on the surface of the water and may appear as
small " rafts '' floating just beneath the surface. A pronounced " eye "
spot develops, when larvae are about 270 p in length, and is present
throughout the remainder of the free-swimming period.
Larvae of C'. virginica may be affected by fungus, rYirdpidium
zoophthorum, and die, but they are much less RUHceptible to this
disease than larvae of M. mercenaria and some other formH.
110.4 x 96.6; 124.2 x 110.4; 151.8 >( 131.1; 165.6 X 144.9; 207.0 X
7
83
The majority of larvae of C. virginica metamorphoses between 275
and 315 p in length, but occasionally free-swimming larvae may be
365 p long. Larvae were grown to metamorphosis at temperatures
ranging from about 17" to 33°C ; at the latter temperature some larvae
metamorphosed in about 12 days. Naked flagellates, such as I. galbana
and M . luthpri, are the best foods, whereas some of the green algae
with thick cell walls, such as certain Chlorelh species, are not readily
utilized by early veligers, especially at comparatively low temperaturea.
Stafford (1912), in his paper on recognition of bivalve larvae in
plankton collections, offered a description and drawings of larvae of
C. virginica of different stages. His description and, especially, the
length-width relationships of the larvae are widely different from ours.
For example, Stafford gives the following length-width (depth)
measurements, in micron8, as typical for oyster larvae: 82-8 x 69.0;
193.2 ; 310.5 x 276.0 ; and 345.0 x 303.6. A comparison with our data
shows that the majority of the above length-width ratios cannot
apply to larvae of C. virginica. For example, we found that among the
130 of our larvae measuring 110 p in length the width varied only from
105 to 125 p. I n other words, none of these larvae were only 96-6 p
wide, as indicated by Stafford. His discrepancies in length-width
ratio are even greater when he gives measurements of larger larvae.
Finally, his larvae always measure more in length than in width
(depth) although, as has already been mentioned, when a length of
about 125 p is reached, the width of the larvae begins to exceed the
length by about 5 to 1 0 p arid contiIiuwi t20 do 80 until metamorphorri8.
Siillivari'fi ( I ! b t H ) ~ n ( ~ ~ ~ ~ i i l ' ( ~ i i i t r i i t ~
t~lrict I ~ t i o ( . ~ ) t i ) i r r o ~ ~ ~ ~ ~ t ~ R
(if' Iiirvrw of
( '. viq/ii/iui JWI- I ~ I I I ~
t * ~L(~II.ILII*.
'l'hie color of larvae varies somewhat with the food, but healthy
larvae are usually a golden brown, particularly in the area of the
digestive diverticulum. Young larvae are usually pinkish-orange en
masse, but this color changes to brown and, later, to almost black as
the larvae grow larger..
Larvae are highly active and remain in suspension throughout the
free-swimming period. Large larvae, 200 p or more in length, have a.
tendency to gather on the surface of the water and may appear as
small " rafts '' floating just beneath the surface. A pronounced " eye "
spot develops, when larvae are about 270 p in length, and is present
throughout the remainder of the free-swimming period.
Larvae of C'. virginica may be affected by fungus, rYirdpidium
zoophthorum, and die, but they are much less RUHceptible to this
disease than larvae of M. mercenaria and some other formH.
110.4 x 96.6; 124.2 x 110.4; 151.8 >( 131.1; 165.6 X 144.9; 207.0 X
7