360
N. BALAKRISHNAN NAIR AND M. SARASWATHY
of them (Bankia (Neobanlcia) barthelewi Bartsch). Lack of appreciation
of the range of variations in the pallets has been responsible for the
creation of a large number of species which later on turn out to be
synonyms. Miller (1923) has shown that in San Francisco Bay the
pallets of Teredo navalis exhibit a wide range of variations. Similarly
Nair (1959) illustrated considerable variations in the size and shape of
the pallets of Nototeredo norvagica from Western Norway. Apart
from the genetic variations, the size and shape of the pallets may
be considerably affected by age and wear and environmental factors.
Drying up of the pallets and " exfoliation " of the periostracal cap are
also likely to give an incorrect picture. Since these structures are constantly put to use to close the opening of the burrow they are subjected
to considerable mechanical wear and tear. They are also chemically
affected by the changes in the nature and composition of the ambient
water. Variations in the nature of such deterioration can also take
place in the pallets of living specimens. Those of Bankia (Nausitora)
jamesi Bartsch have been illustrated by Turner (1966). Heavy settlement
on a restricted substratum may misshapen the pallet in stenomorphic
forms (gartsch, 192311 ; Nak, 1959). Even the two pieces of a single pair
may be so unlike each other that they may be regarded as belonging to
different specimens. Therefore, in any taxonomic consideration at
generic and specific levels based on differences exhibited by the pallets,
the range of variations exhibited by them under different ecological
conditions and due t o age and wear should be carefully considered before
new species are described. The pallets of certain species such as those
of Lyrodus exhibit remarkable variations (Fig. 10). This has led authors
to create new species, most of which turn out to be ecological forms of
the cosmopolitan, Lyrodus pedicellatus Quatrefages.
The mechanism of the pallets in Bankia has been adequately
described, and illustrated by Sigerfoos (1908). Turner (1966) has
recently endeavoured t o trace the evolution of the pallet in the Teredinidae. According to her, during the evolution of the Teredinidae,
following the development of the caecum and the separation of the
intestine from the heart, a major divergence occurred. In response to
the need for an efficient mechanism to close the opening of the burrow
one line accomplished this by adding new segments to the proximal end
of the pallet giving rise to the segmented pallet line-the Bankiinae,
and the other by depositing new material over the entire surface of the
pallet leading to the non-segmented pallet line-the Teredininae. However, May (1929) interpreted this concentric incremental growth in
Teredo navalis as fused segments. The evolution of the segmented
pallet line is quite direct beginning with Nototeredo. The next step is
N. BALAKRISHNAN NAIR AND M. SARASWATHY
of them (Bankia (Neobanlcia) barthelewi Bartsch). Lack of appreciation
of the range of variations in the pallets has been responsible for the
creation of a large number of species which later on turn out to be
synonyms. Miller (1923) has shown that in San Francisco Bay the
pallets of Teredo navalis exhibit a wide range of variations. Similarly
Nair (1959) illustrated considerable variations in the size and shape of
the pallets of Nototeredo norvagica from Western Norway. Apart
from the genetic variations, the size and shape of the pallets may
be considerably affected by age and wear and environmental factors.
Drying up of the pallets and " exfoliation " of the periostracal cap are
also likely to give an incorrect picture. Since these structures are constantly put to use to close the opening of the burrow they are subjected
to considerable mechanical wear and tear. They are also chemically
affected by the changes in the nature and composition of the ambient
water. Variations in the nature of such deterioration can also take
place in the pallets of living specimens. Those of Bankia (Nausitora)
jamesi Bartsch have been illustrated by Turner (1966). Heavy settlement
on a restricted substratum may misshapen the pallet in stenomorphic
forms (gartsch, 192311 ; Nak, 1959). Even the two pieces of a single pair
may be so unlike each other that they may be regarded as belonging to
different specimens. Therefore, in any taxonomic consideration at
generic and specific levels based on differences exhibited by the pallets,
the range of variations exhibited by them under different ecological
conditions and due t o age and wear should be carefully considered before
new species are described. The pallets of certain species such as those
of Lyrodus exhibit remarkable variations (Fig. 10). This has led authors
to create new species, most of which turn out to be ecological forms of
the cosmopolitan, Lyrodus pedicellatus Quatrefages.
The mechanism of the pallets in Bankia has been adequately
described, and illustrated by Sigerfoos (1908). Turner (1966) has
recently endeavoured t o trace the evolution of the pallet in the Teredinidae. According to her, during the evolution of the Teredinidae,
following the development of the caecum and the separation of the
intestine from the heart, a major divergence occurred. In response to
the need for an efficient mechanism to close the opening of the burrow
one line accomplished this by adding new segments to the proximal end
of the pallet giving rise to the segmented pallet line-the Bankiinae,
and the other by depositing new material over the entire surface of the
pallet leading to the non-segmented pallet line-the Teredininae. However, May (1929) interpreted this concentric incremental growth in
Teredo navalis as fused segments. The evolution of the segmented
pallet line is quite direct beginning with Nototeredo. The next step is