THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
359
the food rope towards the mouth. The ciliated groove in apposition
with the branchial groove forms a ciliated tunnel.
Posteriorly in the region of the ctenidia the grooves become shallow
and eventually persist as two ciliated tracts. The cilia of these are unlike those in the groove in being scattered and short. These ciliary tracts
could be traced to the very end of the mantle cavity. Further, the
mantle epithelium along the roof of the epibranchial cavity is produced
into a series of lamellae which project into the cavity especially dorsolaterally. There is greater development of muscle fibres along the roof
of the epibranchial chamber and the epithelial lining is interspersed
with gland cells. Nair (1957a) has recorded a concentration of mucous
glands along the dorso-median line of the supra-branchial cavity and
Sigerfoos (1908), noted a specialized type of gland in the posterior part
but neither of these occurs in Nausitora hedleyi. A congregation of
glandular structures has, however, been noted mid-dorsally at the
beginning of the siphons in N . hedlleyi.
2. The adductor muscles
The adductor muscles represent local enlargements and cross fusion
of the pallid muscles (Yonge, 1953). The anterior adductor muscle is
inserted on the ventral inner edge of the anterior lobe of each valve and
the posterior adductor has its attachment on the inner face of the
posterior wing of the shell-the auricle. Together they bring about a
powerful rocking movement. The ability for alternate contraction of
these muscles and the absence of the ligament help the shell valves to
move on a dorso-ventral axis-and supply the shell with power for
drilling. Pinkish in hue, they are composed of powerful strands of
striated muscles. In N . hedleyi the area occupied by the anterior adductor is only a tenth of that of the posterior adductor; both are
approximately bean-shaped.
3. The pallets
The pallets are unique structures characteristic of shipworms and
show distinguishable differences in the various genera. These variations
are not only characteristic of the different species but also of individuals
of the same species. In shipworm taxonomy differences in the shape
and proportions of the parts of the pallets have been regarded as important characters (see Bartsch, 1922,1923,1927,1927a; Iredale et al., 1932;
Moll, 1941 ; Roch, 1940 ; Nair, 1954). In many cases, the nature of the
pallets alone has been considered as the basis of specific identification
e.g. (Teredo (Teredo) beuufortanu Bartsch). In some instances new
species have been created on the basis of a single pair of pallets or a few
359
the food rope towards the mouth. The ciliated groove in apposition
with the branchial groove forms a ciliated tunnel.
Posteriorly in the region of the ctenidia the grooves become shallow
and eventually persist as two ciliated tracts. The cilia of these are unlike those in the groove in being scattered and short. These ciliary tracts
could be traced to the very end of the mantle cavity. Further, the
mantle epithelium along the roof of the epibranchial cavity is produced
into a series of lamellae which project into the cavity especially dorsolaterally. There is greater development of muscle fibres along the roof
of the epibranchial chamber and the epithelial lining is interspersed
with gland cells. Nair (1957a) has recorded a concentration of mucous
glands along the dorso-median line of the supra-branchial cavity and
Sigerfoos (1908), noted a specialized type of gland in the posterior part
but neither of these occurs in Nausitora hedleyi. A congregation of
glandular structures has, however, been noted mid-dorsally at the
beginning of the siphons in N . hedlleyi.
2. The adductor muscles
The adductor muscles represent local enlargements and cross fusion
of the pallid muscles (Yonge, 1953). The anterior adductor muscle is
inserted on the ventral inner edge of the anterior lobe of each valve and
the posterior adductor has its attachment on the inner face of the
posterior wing of the shell-the auricle. Together they bring about a
powerful rocking movement. The ability for alternate contraction of
these muscles and the absence of the ligament help the shell valves to
move on a dorso-ventral axis-and supply the shell with power for
drilling. Pinkish in hue, they are composed of powerful strands of
striated muscles. In N . hedleyi the area occupied by the anterior adductor is only a tenth of that of the posterior adductor; both are
approximately bean-shaped.
3. The pallets
The pallets are unique structures characteristic of shipworms and
show distinguishable differences in the various genera. These variations
are not only characteristic of the different species but also of individuals
of the same species. In shipworm taxonomy differences in the shape
and proportions of the parts of the pallets have been regarded as important characters (see Bartsch, 1922,1923,1927,1927a; Iredale et al., 1932;
Moll, 1941 ; Roch, 1940 ; Nair, 1954). In many cases, the nature of the
pallets alone has been considered as the basis of specific identification
e.g. (Teredo (Teredo) beuufortanu Bartsch). In some instances new
species have been created on the basis of a single pair of pallets or a few