404
N. BALAKRISHNAN NAIR AND M. SARASWATHY
x 70 p in size. Through allometric growth the valves assume a bulbous
form around the eleventh day. By about 15 days the shell valves increase to 250 x 2 6 5 p the height becoming distinctly more than the
length. The valves have bold and dark rims. It is interesting to note
that the shape and nature of the valves of the late veliger of even such
widely different genera as Teredo and Bankia seem to be remarkably
similar (Sullivan, 1948 ; Quayle, 1953 ; Nair, 1956a ; Loosanoff, Davis
and Chanley, 1966). The valves of these two genera are also similar in
possessing three provincular teeth on the right valve and two on the left
as also reported in Lyrodus pedicellatus by Rancurel (1951). The valves
of the late veliger shell are equilateral, characteristically convex with
high steeply slanting, narrow shoulders, prominent knob-like umbones,
and short sharply curved bases (Nair, 1956a).
Many authors have given essentially similar descriptions of the
teredinid larvae (Sigerfoos, 1896, 1908 ; Borisjak, 1905 ; Nakazawa,
1915 ; Miyazaki, 1935 ; Lebour, 1938, 1946 ; Jarrgensen, 1946 ; Sullivan,
1948; Rees, 1950; Quayle, 1952; Isham and Tierney, 1953; Nab,
1956a). Nevertheless, the size at which free swimming planktonic larvae
are ready for settlement varies. Thus, the late larvae of an oviparous
species Teredo norvegica measure 380 p in length (Lebour, 1938), those
of Bankia indica 273 x 265 p (height x length) on an average, those
of the incubatory species, Teredo navalis 235 x 2 1 5 p (Imai et al.,
1950) in Japanese waters and 250 x 220 p in Malpique Bay (Sullivan,
1948). The largest swimming larvae in the cultures of Loosanoff and
Davis (1963) were approximately 231 x 200 p.
The colour of the larvae darkens soon after they reach 1 O O p in
length. The larvae of advanced stages of Teredo navalis do not develop
an eye, the foot is extremely slender and worm-like and they attach
themselves to the substratum by a byssus (Loosanoff and Davis, 1963).
Imai et al. (1950) observed that neither foot, otocyst nor gill filaments
appear before the larvae reach the size of 215 x 200 p but Loosanoff
and Davis (1963) observed the appearance of these in larvae at least
15 p smaller.
These larvae lead a pelagic life swimming actively and feeding on
plankton. They are hardy, surviving in laboratory bowls in which the
water was not changed for 9 days. The larvae of Bankia indica when
about 17 days old are ready for settling on wood (Nair, 1956a). Preparatory to this they settle and then crawl on the surface of the wood
pieces left in the container (Fig. 33). The period of crawling over the
substratum varies greatly and may extend for up to an hour. During
this period activity diminishes till the foot comes to rest in a depression
on the surface of the wood. Subsequently the shell is lifted while byssal
N. BALAKRISHNAN NAIR AND M. SARASWATHY
x 70 p in size. Through allometric growth the valves assume a bulbous
form around the eleventh day. By about 15 days the shell valves increase to 250 x 2 6 5 p the height becoming distinctly more than the
length. The valves have bold and dark rims. It is interesting to note
that the shape and nature of the valves of the late veliger of even such
widely different genera as Teredo and Bankia seem to be remarkably
similar (Sullivan, 1948 ; Quayle, 1953 ; Nair, 1956a ; Loosanoff, Davis
and Chanley, 1966). The valves of these two genera are also similar in
possessing three provincular teeth on the right valve and two on the left
as also reported in Lyrodus pedicellatus by Rancurel (1951). The valves
of the late veliger shell are equilateral, characteristically convex with
high steeply slanting, narrow shoulders, prominent knob-like umbones,
and short sharply curved bases (Nair, 1956a).
Many authors have given essentially similar descriptions of the
teredinid larvae (Sigerfoos, 1896, 1908 ; Borisjak, 1905 ; Nakazawa,
1915 ; Miyazaki, 1935 ; Lebour, 1938, 1946 ; Jarrgensen, 1946 ; Sullivan,
1948; Rees, 1950; Quayle, 1952; Isham and Tierney, 1953; Nab,
1956a). Nevertheless, the size at which free swimming planktonic larvae
are ready for settlement varies. Thus, the late larvae of an oviparous
species Teredo norvegica measure 380 p in length (Lebour, 1938), those
of Bankia indica 273 x 265 p (height x length) on an average, those
of the incubatory species, Teredo navalis 235 x 2 1 5 p (Imai et al.,
1950) in Japanese waters and 250 x 220 p in Malpique Bay (Sullivan,
1948). The largest swimming larvae in the cultures of Loosanoff and
Davis (1963) were approximately 231 x 200 p.
The colour of the larvae darkens soon after they reach 1 O O p in
length. The larvae of advanced stages of Teredo navalis do not develop
an eye, the foot is extremely slender and worm-like and they attach
themselves to the substratum by a byssus (Loosanoff and Davis, 1963).
Imai et al. (1950) observed that neither foot, otocyst nor gill filaments
appear before the larvae reach the size of 215 x 200 p but Loosanoff
and Davis (1963) observed the appearance of these in larvae at least
15 p smaller.
These larvae lead a pelagic life swimming actively and feeding on
plankton. They are hardy, surviving in laboratory bowls in which the
water was not changed for 9 days. The larvae of Bankia indica when
about 17 days old are ready for settling on wood (Nair, 1956a). Preparatory to this they settle and then crawl on the surface of the wood
pieces left in the container (Fig. 33). The period of crawling over the
substratum varies greatly and may extend for up to an hour. During
this period activity diminishes till the foot comes to rest in a depression
on the surface of the wood. Subsequently the shell is lifted while byssal