THE BIOLOGY OF WOOD-BORING TEREDINID MOLLUSCS
381
concerned with plankton feeding. In the Teredinidae consequent on a
shift in emphasis from plankton feeding to a diet consisting chiefly of
wood fragments, the ctenidia have undergone relative changes. In two
genera, Teredora and Uperotus, the ctenidia extend the entire length of
the animal from the base of the siphons to the mouth (Saraswathy and
Nair, 1965). Others have discontinuous ctenidia.
I n Nausitora hedleyi, N . dunlopei and Neoteredo reynei, the ctenidia
are short with rather truncate lamellae, an extreme case of reduction
in contrast to the condition in the genera Uperotw and Teredora. The
condition in others seems to be intermediate between these
extremes.
This apparent difference in the extent and efficiency of the ckenidium
is interestingly correlated with the extent of the development of the
apecialized region of the digestive diverticula which probably represents
the region for the reception and intracellular digestion of, wood particles. In Teredora princesae where the ctenidia are well developed with
the most extensive gills bearing long gill lamellae, the specialized part
of the digestive diverticula cannot be seen even in serial sections.
Probably, this species feeds almost entirely on plankton. In Teredo
furcifera where the ctenidia are of medium size, the specialized part is
distinguishable histologically while in Nausitora hedleyi where the
ctenidia are considerably reduced in extent the specialized region forms
the dominant part of the digestive diverticula. Nawitora fusticula is
interesting in that it bears short truncate gills and apparently has
secondarily returned to filter feeding by adding the filtering mechanism
(Fig. 12, h) to the end of the inhalant siphon (Turner, 1966). I n all
cases, however, the ctenidia must assist in feeding by the collection of
the small amounts of nannoplankton needed to supplement the scarce
nitrogenous constituents present in the wood. Morton (1970), who
describes the various cilary currents in Teredo nacalis and Lyrodus
pedicellatus, finds little evidence of selection. Both wood particles and
plankton enter the mouth.
9. Glands of Deshayes
These organs are peculiar to shipworms. Sigerfoos (1908) who named
them described them in different degrees of development in Teredo
dilatata, Bankia gouldi and Teredo navalis and distinguished three
groups, one investing the gill lamellae, another in the tissue beneath
the umbonal region of the shell and the third inside the afferent
branchial vein. Deshayes (1848) had considered that these were
separate structures with different functions.
The first group occur packed within the interfilamentar spaces of
381
concerned with plankton feeding. In the Teredinidae consequent on a
shift in emphasis from plankton feeding to a diet consisting chiefly of
wood fragments, the ctenidia have undergone relative changes. In two
genera, Teredora and Uperotus, the ctenidia extend the entire length of
the animal from the base of the siphons to the mouth (Saraswathy and
Nair, 1965). Others have discontinuous ctenidia.
I n Nausitora hedleyi, N . dunlopei and Neoteredo reynei, the ctenidia
are short with rather truncate lamellae, an extreme case of reduction
in contrast to the condition in the genera Uperotw and Teredora. The
condition in others seems to be intermediate between these
extremes.
This apparent difference in the extent and efficiency of the ckenidium
is interestingly correlated with the extent of the development of the
apecialized region of the digestive diverticula which probably represents
the region for the reception and intracellular digestion of, wood particles. In Teredora princesae where the ctenidia are well developed with
the most extensive gills bearing long gill lamellae, the specialized part
of the digestive diverticula cannot be seen even in serial sections.
Probably, this species feeds almost entirely on plankton. In Teredo
furcifera where the ctenidia are of medium size, the specialized part is
distinguishable histologically while in Nausitora hedleyi where the
ctenidia are considerably reduced in extent the specialized region forms
the dominant part of the digestive diverticula. Nawitora fusticula is
interesting in that it bears short truncate gills and apparently has
secondarily returned to filter feeding by adding the filtering mechanism
(Fig. 12, h) to the end of the inhalant siphon (Turner, 1966). I n all
cases, however, the ctenidia must assist in feeding by the collection of
the small amounts of nannoplankton needed to supplement the scarce
nitrogenous constituents present in the wood. Morton (1970), who
describes the various cilary currents in Teredo nacalis and Lyrodus
pedicellatus, finds little evidence of selection. Both wood particles and
plankton enter the mouth.
9. Glands of Deshayes
These organs are peculiar to shipworms. Sigerfoos (1908) who named
them described them in different degrees of development in Teredo
dilatata, Bankia gouldi and Teredo navalis and distinguished three
groups, one investing the gill lamellae, another in the tissue beneath
the umbonal region of the shell and the third inside the afferent
branchial vein. Deshayes (1848) had considered that these were
separate structures with different functions.
The first group occur packed within the interfilamentar spaces of