THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
357
mantle in the posterior region below the ctenidia reveals a greatly
thickened median swelling (Saraswathy and Nair, 1971). The exact
significance of these ridges which are absent in Teredo navalis and
T . megotara (Purchon, 1941) is not clear. These folds probably form
incomplete longitudinal partitions of the mantle chamber helping to
some extent in regulating the movement of waste matter in the mantle
cavity.
The free edge of the mantle is thickened and consists of the outer,
middle and inner folds typical of bivalves. Between the middle and the
outer fold runs the periostracal groove. The middle lobe which is
primarily sensory is devoid of any special sensory structures except at
the tip of the siphons where sensory papillae occur. The outer fold and
the periostracal groove are secretory, and so responsible for the ridges
and denticles resulting in the growth of the shell by marginal increment.
Periostracal fibres coalesce to form thick strands which pass over the
edge of the shell.
Within the connective tissue, especially of the anterior region of
Naueitora hedleyi granular bodies appearing in serial sections have been
shown to be developmental stages of certain parasitic protozoans,
probably of Boveria as described by Ikeda and Ozaki (1918).
Certain structures are associated with the connective tissue of the
mantle. Hancock (1845) considered them t o be silicious particles responsible for the formation of the burrow. Deshayes (1848) observed
non-nucleated mucous cells. Sigerfoos ( 1908) considered they were
reserves of calcium used for the formation and thickening of the calcareous tube which lines the burrow. Nair (1957a) observed spherical
nodular bodies in fresh connective tissue which were opaque in transmitted light and white in reflected light, soluble in water and turning
russet when treated with iodine. Alcohol in which specimens had been
preserved turned turbid. These structures were probably glycogen.
Twarog (quoted by Turner, 1966) found that the " granules " in the
mantle were insoluble in acid, in alkali and in distilled water and did not
change colour when treated with iodine and so concluded the material
was not glycogen. On prolonged heating a carbon residue was left
suggesting that the substance is at least partially organic. The contradictory nature of these observations suggests that the structures
examined were not all the same.
In the genus Kuphw the unusually thick mantle is composed of
seven layers, an outer epithelium followed in order by thin layers of
circular and longitudinal muscles, a thick layer of transverse muscles
again by thin layers circular and longitudinal muscles and by the inner
epithelium (Turner, 1966).
357
mantle in the posterior region below the ctenidia reveals a greatly
thickened median swelling (Saraswathy and Nair, 1971). The exact
significance of these ridges which are absent in Teredo navalis and
T . megotara (Purchon, 1941) is not clear. These folds probably form
incomplete longitudinal partitions of the mantle chamber helping to
some extent in regulating the movement of waste matter in the mantle
cavity.
The free edge of the mantle is thickened and consists of the outer,
middle and inner folds typical of bivalves. Between the middle and the
outer fold runs the periostracal groove. The middle lobe which is
primarily sensory is devoid of any special sensory structures except at
the tip of the siphons where sensory papillae occur. The outer fold and
the periostracal groove are secretory, and so responsible for the ridges
and denticles resulting in the growth of the shell by marginal increment.
Periostracal fibres coalesce to form thick strands which pass over the
edge of the shell.
Within the connective tissue, especially of the anterior region of
Naueitora hedleyi granular bodies appearing in serial sections have been
shown to be developmental stages of certain parasitic protozoans,
probably of Boveria as described by Ikeda and Ozaki (1918).
Certain structures are associated with the connective tissue of the
mantle. Hancock (1845) considered them t o be silicious particles responsible for the formation of the burrow. Deshayes (1848) observed
non-nucleated mucous cells. Sigerfoos ( 1908) considered they were
reserves of calcium used for the formation and thickening of the calcareous tube which lines the burrow. Nair (1957a) observed spherical
nodular bodies in fresh connective tissue which were opaque in transmitted light and white in reflected light, soluble in water and turning
russet when treated with iodine. Alcohol in which specimens had been
preserved turned turbid. These structures were probably glycogen.
Twarog (quoted by Turner, 1966) found that the " granules " in the
mantle were insoluble in acid, in alkali and in distilled water and did not
change colour when treated with iodine and so concluded the material
was not glycogen. On prolonged heating a carbon residue was left
suggesting that the substance is at least partially organic. The contradictory nature of these observations suggests that the structures
examined were not all the same.
In the genus Kuphw the unusually thick mantle is composed of
seven layers, an outer epithelium followed in order by thin layers of
circular and longitudinal muscles, a thick layer of transverse muscles
again by thin layers circular and longitudinal muscles and by the inner
epithelium (Turner, 1966).