THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
427
live as long as normal ones, they are unable to increase the length or
diameter of their tubes. Their only growth, he observed, was a regular
addition of the denticulate ridges and an increase in the thickness of
the shell and abnormalities in the nature and the relative proportions
of the different parts of the shell. While normal specimens grew to a
length of 10 mm in less than 2 weeks time, stenomorplzs, even at the
age of 10 months remained unchanged a t this length. Edmondson
(1942) noted " stenomorphic ) ) forms in Teredo milleri and T . gregoreyi
from Hawaii. I n Bankia indica of Madras, the growth as reported by
Nair (1960) is 9 mm in 17 days, 23 mm in 32 days, 142 mm in 68 days,
224 mm in 95 days, 257 mm in 125 days, 274 mm in 165 days, 290 mm
in 191 days and 302 mm in 219 days, representing an average rate of
boring of 4.3 cmlmonth. Data on growth in length of the animal,
growth in the size of the shell, increase in the number of ridges on the
shell valves and increase in the weight of the animal indicate that
growth is very rapid during the first 90 days and thereafter slackens
and the trend indicates that growth becomes negligible at the end of
about 220days. Retardation of growth has been attributed to depletion of the woody material on the panel as a result of overcrowding.
Growth rate studies on B. campanellata (Nagabhushanam, 1959) revealed a growth of nearly 51.5 mm/month. Maximum growth during
the year was recorded in December when the burrow length increased
by 60 mm. Teredo furcillatus in Visakhapatnam harbour was found to
reach a maximum of 90 mm, dry weight 110 mg and wet weight 319 mg
at the end of 5 months. Maximum growth was recorded in May when
the burrow length increased by about 29 mm. Maximum growth coincided with the highest temperature, i.e. 30-9"C (Nagabhushanam,
1961). We assessed the growth of the estuarine N . hedleyi in the
indigenous timber Hangifera indica. The length of the burrow, wet and
dry weights of the animal, weight of the shells and of the pallets, the
number of denticulated ridges over the shell, length and height of the
shell, proportion of the pallet blade and stalk and the number of cones
that form the blade were all considered over a period of nearly 6 months.
The salient features of the growth rates of this species assessed on the
basis of the above characters were as follows : growth was rapid during
the period between 45 and 135 days after settlement (13.9.65to 12.12.65)
with the maximum growth between 105 and 120 days of age. Thereafter, growth slackened and the trend indicated that growth was
negligible a t the end of 150 days. This might be owing to retardation in
growth as a result of the effects of overcrowding and the depletion of
the substrate preventing further boring. It might also be the effect of
an increasing and unfavourable salinity. While reasonably valid cor-
427
live as long as normal ones, they are unable to increase the length or
diameter of their tubes. Their only growth, he observed, was a regular
addition of the denticulate ridges and an increase in the thickness of
the shell and abnormalities in the nature and the relative proportions
of the different parts of the shell. While normal specimens grew to a
length of 10 mm in less than 2 weeks time, stenomorplzs, even at the
age of 10 months remained unchanged a t this length. Edmondson
(1942) noted " stenomorphic ) ) forms in Teredo milleri and T . gregoreyi
from Hawaii. I n Bankia indica of Madras, the growth as reported by
Nair (1960) is 9 mm in 17 days, 23 mm in 32 days, 142 mm in 68 days,
224 mm in 95 days, 257 mm in 125 days, 274 mm in 165 days, 290 mm
in 191 days and 302 mm in 219 days, representing an average rate of
boring of 4.3 cmlmonth. Data on growth in length of the animal,
growth in the size of the shell, increase in the number of ridges on the
shell valves and increase in the weight of the animal indicate that
growth is very rapid during the first 90 days and thereafter slackens
and the trend indicates that growth becomes negligible at the end of
about 220days. Retardation of growth has been attributed to depletion of the woody material on the panel as a result of overcrowding.
Growth rate studies on B. campanellata (Nagabhushanam, 1959) revealed a growth of nearly 51.5 mm/month. Maximum growth during
the year was recorded in December when the burrow length increased
by 60 mm. Teredo furcillatus in Visakhapatnam harbour was found to
reach a maximum of 90 mm, dry weight 110 mg and wet weight 319 mg
at the end of 5 months. Maximum growth was recorded in May when
the burrow length increased by about 29 mm. Maximum growth coincided with the highest temperature, i.e. 30-9"C (Nagabhushanam,
1961). We assessed the growth of the estuarine N . hedleyi in the
indigenous timber Hangifera indica. The length of the burrow, wet and
dry weights of the animal, weight of the shells and of the pallets, the
number of denticulated ridges over the shell, length and height of the
shell, proportion of the pallet blade and stalk and the number of cones
that form the blade were all considered over a period of nearly 6 months.
The salient features of the growth rates of this species assessed on the
basis of the above characters were as follows : growth was rapid during
the period between 45 and 135 days after settlement (13.9.65to 12.12.65)
with the maximum growth between 105 and 120 days of age. Thereafter, growth slackened and the trend indicated that growth was
negligible a t the end of 150 days. This might be owing to retardation in
growth as a result of the effects of overcrowding and the depletion of
the substrate preventing further boring. It might also be the effect of
an increasing and unfavourable salinity. While reasonably valid cor-