REARING OF BIVALVE MOLLUSKS
127
species. The fact that Jsrgensen stated on several occasions that
metamorphosis of M. arenuria may occur upon attainment of a much
smaller size than 300p strongly suppo~%s our opinion. For example,
Jsrgensen mentioned that in Ringkbing Fjord the size of larvae at
metamorphosis in shallow water varies between 200 and 225p, thus
being within the size range observed in oiir cultures.
S. Teredo nuvalis Linn6
Larvae of T . navalis have been described by many authors, including
Jsrgensen (1946), Sullivan (1948) and, ako, Imai, Hatanaka and Sato
(1950), who gave a good description of the method of rearing them.
In our laboratory adult T . navali9 wcre conditioned to spawn as
early as the fist part of December. This was done by placing pieces of
wood, containing wood-borers, in sea water maintained at a temperature between 16" and 20°C. Spawning occurred at temperatures of
14°C and higher, and larvae were released at temperatures ranging
from about 16" to 20°C. Grave (1928) reported that spawning of
T. nuvalis began when the water temperature reached 11" to 12°C.
Imai et al. (1950b), however, found that spawning begins when the
water temperature reaches 18°C. Sullivan's (1948) data closely agree
with ours, that spawning and swarming niay occur at approximately
15°C.
Although T . navalis is naturally larviparous, both recentlyfertilized eggs and immature larvae removed from the gill chambers
of the parents developed normally past metamorphosis. The diameter
of unfertilized eggs varied between 50 and 60 p, agreeing with measurements given by Jsrgensen (1946) and Gofitello et al. (1967). In the
diasected adults, however, most of the egg(i found were either already
fertilized or immature, thus presenting difiiculty in obtaining reliable
egg measurements.
The smallest larvae released in natur a1 H warm ings at our laboratory
measured only 80 x 7 0 p , whilo the largejt larvae found in the gill
chamber of the mother.were 9Op long, or approximately lop longer
than reported by Jrargensen (1946). Evidently, the length of larvae
at the time of release may vary by at least 20 p. Imai et al. (1950b)
indioated that the mean size at the time of release is 85 x 72p. Our
observations that the average size of just-released Teredo laxvae is
between 86 and 9 6 p &re in agreement with those of Sullivan (1948),
Jmgensen (1946) and Imai et al. (195Oa). We cannot, however, accept the
conclusion of Lane et al. (1954) who maintained that larvae are about
250 p in size when released from the gill chamber.
Eggs, in early stages of development, taken from the gill chamber
127
species. The fact that Jsrgensen stated on several occasions that
metamorphosis of M. arenuria may occur upon attainment of a much
smaller size than 300p strongly suppo~%s our opinion. For example,
Jsrgensen mentioned that in Ringkbing Fjord the size of larvae at
metamorphosis in shallow water varies between 200 and 225p, thus
being within the size range observed in oiir cultures.
S. Teredo nuvalis Linn6
Larvae of T . navalis have been described by many authors, including
Jsrgensen (1946), Sullivan (1948) and, ako, Imai, Hatanaka and Sato
(1950), who gave a good description of the method of rearing them.
In our laboratory adult T . navali9 wcre conditioned to spawn as
early as the fist part of December. This was done by placing pieces of
wood, containing wood-borers, in sea water maintained at a temperature between 16" and 20°C. Spawning occurred at temperatures of
14°C and higher, and larvae were released at temperatures ranging
from about 16" to 20°C. Grave (1928) reported that spawning of
T. nuvalis began when the water temperature reached 11" to 12°C.
Imai et al. (1950b), however, found that spawning begins when the
water temperature reaches 18°C. Sullivan's (1948) data closely agree
with ours, that spawning and swarming niay occur at approximately
15°C.
Although T . navalis is naturally larviparous, both recentlyfertilized eggs and immature larvae removed from the gill chambers
of the parents developed normally past metamorphosis. The diameter
of unfertilized eggs varied between 50 and 60 p, agreeing with measurements given by Jsrgensen (1946) and Gofitello et al. (1967). In the
diasected adults, however, most of the egg(i found were either already
fertilized or immature, thus presenting difiiculty in obtaining reliable
egg measurements.
The smallest larvae released in natur a1 H warm ings at our laboratory
measured only 80 x 7 0 p , whilo the largejt larvae found in the gill
chamber of the mother.were 9Op long, or approximately lop longer
than reported by Jrargensen (1946). Evidently, the length of larvae
at the time of release may vary by at least 20 p. Imai et al. (1950b)
indioated that the mean size at the time of release is 85 x 72p. Our
observations that the average size of just-released Teredo laxvae is
between 86 and 9 6 p &re in agreement with those of Sullivan (1948),
Jmgensen (1946) and Imai et al. (195Oa). We cannot, however, accept the
conclusion of Lane et al. (1954) who maintained that larvae are about
250 p in size when released from the gill chamber.
Eggs, in early stages of development, taken from the gill chamber