REARING O F BIVALVE MOLLUSKS
123
that the most recent description of what were assumed to be larvae
of M d r a (= Spisulu) solidissinla was reported by Sullivan (1948). She
gave the minimum size of straight-hinge larvae as about 95 x 80 p,
which is approximately 15 p longer than usually found in our cultures,
while the maximum size of 270 x 2 4 5 p closely agreed with our
measurements. In both instances the length-width relationship given
by Sullivan falls near the median line of length-width relationships
which we found for larvae of M. solidissima.
In describing larvae of a related form, Spisula subtruncata, Jlargensen (1946) reported that veligers are about 400 p at the time of
metamorphosis. Kandler (1926) stated, however, that the length of
this species at metamorphosis is only 3lOp. Considering that lmai
p t d . (1953) found the maximum size of' larvae of M a c h ( Spisuln)
sachalinerisis to be about 270 p, virtually the same as we found for
M . solidissima, and because Imai's conclusions and ours are based on
measurements of larvae of a known origin, we think that Kandler's
measurements are more realistic than Jsrgensen's and that the latter
was probably describing larvae other than those belonging to the genus
Hactra (= Spisula). The same consideration leads us to believe that the
descriptions and measurements offered by Rees ( 1950) of advanced
stages of larvae presumably of the superfamily Mactracea, including
Spisula solida (360 p ) and Spisula plliptica (355 p), are really those of
some other species.
R. Mya arenaria Linn6
Our efforts to induce spawning of M. arenaria were confined largely
to the period extending from March until the middle of July. Several
groups of these clams were also conditioned and Hpawnwl in winter.
Moreover, to induce spawning of' evcn well-coriditionr:~l arid rtpjiitrwi t l y
ripe M. arenaria is difficult, nevr:rthc,l A f!:HH.
In developing a method to indur:c: fipawrlirig of t l i c : ~ : cliirrifi wv f.rtc:tj
many approachw, iiicliitlirig niichlwr i w l grii~liid d i r m p f i 111 wrr1,t.r
tc*m p r R 1 , i i rv , (4 i i ~ r
I ~ P H i r i Ii f I , ~ i i l
I i I i 1,y , tiy(lroHtiLtic prt:wu rf., light
inkiwities and the addition of sex protlucis. Usually, none of theRe
worked. The only method that proved to he successful with some
regularity consisted of subjecting ripe clams to water of relatively
high temperature, of about 26" to 28"C, for long period8 often extending
from 6 to 8 hr and adding, during this time, a suspension of sex products. Many clams spawned profusely when this method was employed
and discharged a large number of c g p , I)ut a high perccmtage (Jf these
eggs usually dt~velopeti into abnormal larva(..
Belding (1931) reported the diametcr of the average egg of the
123
that the most recent description of what were assumed to be larvae
of M d r a (= Spisulu) solidissinla was reported by Sullivan (1948). She
gave the minimum size of straight-hinge larvae as about 95 x 80 p,
which is approximately 15 p longer than usually found in our cultures,
while the maximum size of 270 x 2 4 5 p closely agreed with our
measurements. In both instances the length-width relationship given
by Sullivan falls near the median line of length-width relationships
which we found for larvae of M. solidissima.
In describing larvae of a related form, Spisula subtruncata, Jlargensen (1946) reported that veligers are about 400 p at the time of
metamorphosis. Kandler (1926) stated, however, that the length of
this species at metamorphosis is only 3lOp. Considering that lmai
p t d . (1953) found the maximum size of' larvae of M a c h ( Spisuln)
sachalinerisis to be about 270 p, virtually the same as we found for
M . solidissima, and because Imai's conclusions and ours are based on
measurements of larvae of a known origin, we think that Kandler's
measurements are more realistic than Jsrgensen's and that the latter
was probably describing larvae other than those belonging to the genus
Hactra (= Spisula). The same consideration leads us to believe that the
descriptions and measurements offered by Rees ( 1950) of advanced
stages of larvae presumably of the superfamily Mactracea, including
Spisula solida (360 p ) and Spisula plliptica (355 p), are really those of
some other species.
R. Mya arenaria Linn6
Our efforts to induce spawning of M. arenaria were confined largely
to the period extending from March until the middle of July. Several
groups of these clams were also conditioned and Hpawnwl in winter.
Moreover, to induce spawning of' evcn well-coriditionr:~l arid rtpjiitrwi t l y
ripe M. arenaria is difficult, nevr:rthc,l A f!:HH.
In developing a method to indur:c: fipawrlirig of t l i c : ~ : cliirrifi wv f.rtc:tj
many approachw, iiicliitlirig niichlwr i w l grii~liid d i r m p f i 111 wrr1,t.r
tc*m p r R 1 , i i rv , (4 i i ~ r
I ~ P H i r i Ii f I , ~ i i l
I i I i 1,y , tiy(lroHtiLtic prt:wu rf., light
inkiwities and the addition of sex protlucis. Usually, none of theRe
worked. The only method that proved to he successful with some
regularity consisted of subjecting ripe clams to water of relatively
high temperature, of about 26" to 28"C, for long period8 often extending
from 6 to 8 hr and adding, during this time, a suspension of sex products. Many clams spawned profusely when this method was employed
and discharged a large number of c g p , I)ut a high perccmtage (Jf these
eggs usually dt~velopeti into abnormal larva(..
Belding (1931) reported the diametcr of the average egg of the