THE BIOLOGY OF WOOD-BORING TEREDINID MOLLUSCS
409
Barger, 1926) confirmed the former, but not the latter, conclusion.
Further work on this is needed.
Settlement of the larvae has been followed in certain species. I n
T. pedicellata settlement takes place preferably after 24 and 48 h of free
swimming existence (see Lane, 1955). On settlement the larva crawls
actively with the aid of the foot and with its aid selects a satisfactory
locus for penetration of the wood (Fig. 33). Isham and Tierney (1953)
have shown that the wood must be properly conditioned for penetration and this involves among others saturation with water and the
development of a suitable microflora and fauna (Becker and Kohlmeyer, 1958 ; Nair, 1965).
In T. pedicellata Isham and Tierney (1953) report a profound change
in behaviour 24 h after release from the parent (Fig. 33). The larva
changes the mode of locomotion from swimming t o crawling over the
available substrata using its highly mobile and sensory foot t o produce
" a lurching locomotor pattern, searching, probing and prospecting the
surface of the timber for a suitable locus for penetration ". During the
process of penetration, according to Lane (1955) " the shells are rocked
rhythmically back and forth in a rough scraping movement, the foot
meanwhile industrially sweeping the surface of the spot where penetration is t o occur. Before long, a small heap of debris is cleared from
beneath the shells by the foot. This accumulates as a conical pile
within which the larvae may still be observed to move. The shell soon
becomes calcified, teeth begin to appear on the shell valves. Soon the
animal becomes completely buried in the wood that is to constitute its
shelter for the rest of its life." At the time of initial penetration, the
larval shell valves are of conchyolin and without denticulations, the
mobile foot is unarmed but the larva possesses considerable concentrations of cellulase even at this stage. Taking all into consideration
Lane (1959) concludes that initial penetration is accomplished by both
mechanical and chemical means.
X. THE SEASON OF SETTLEMENT
The time of settlement is of special interest apart from its biological
importance because it is then that the infective free swimming larvae
come into contact with fresh surfaces and experience the effect of
preservatives used on them. Precise knowledge of the times of settlement of the different species in a locality is of importance in connection
with such operations as replacements, dry docking and repainting of
wooden boats, pile driving, etc. Biologically, the period and extent of
settlement are significant since they are reflections of the breeding season
and a reliable measure of their breeding success. This is due to the fact
409
Barger, 1926) confirmed the former, but not the latter, conclusion.
Further work on this is needed.
Settlement of the larvae has been followed in certain species. I n
T. pedicellata settlement takes place preferably after 24 and 48 h of free
swimming existence (see Lane, 1955). On settlement the larva crawls
actively with the aid of the foot and with its aid selects a satisfactory
locus for penetration of the wood (Fig. 33). Isham and Tierney (1953)
have shown that the wood must be properly conditioned for penetration and this involves among others saturation with water and the
development of a suitable microflora and fauna (Becker and Kohlmeyer, 1958 ; Nair, 1965).
In T. pedicellata Isham and Tierney (1953) report a profound change
in behaviour 24 h after release from the parent (Fig. 33). The larva
changes the mode of locomotion from swimming t o crawling over the
available substrata using its highly mobile and sensory foot t o produce
" a lurching locomotor pattern, searching, probing and prospecting the
surface of the timber for a suitable locus for penetration ". During the
process of penetration, according to Lane (1955) " the shells are rocked
rhythmically back and forth in a rough scraping movement, the foot
meanwhile industrially sweeping the surface of the spot where penetration is t o occur. Before long, a small heap of debris is cleared from
beneath the shells by the foot. This accumulates as a conical pile
within which the larvae may still be observed to move. The shell soon
becomes calcified, teeth begin to appear on the shell valves. Soon the
animal becomes completely buried in the wood that is to constitute its
shelter for the rest of its life." At the time of initial penetration, the
larval shell valves are of conchyolin and without denticulations, the
mobile foot is unarmed but the larva possesses considerable concentrations of cellulase even at this stage. Taking all into consideration
Lane (1959) concludes that initial penetration is accomplished by both
mechanical and chemical means.
X. THE SEASON OF SETTLEMENT
The time of settlement is of special interest apart from its biological
importance because it is then that the infective free swimming larvae
come into contact with fresh surfaces and experience the effect of
preservatives used on them. Precise knowledge of the times of settlement of the different species in a locality is of importance in connection
with such operations as replacements, dry docking and repainting of
wooden boats, pile driving, etc. Biologically, the period and extent of
settlement are significant since they are reflections of the breeding season
and a reliable measure of their breeding success. This is due to the fact