THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
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gouldi (Bartsch), B. setacea (Tryon) and B. carinata (Gray), variations
exist in different genera.
While the labial palps are free and distinguishable in Teredora
princesae, T . malleolus, Uperotus clavus, U. rehderi, Psiloteredo megotara,
Nototeredo norvagica, N . knoxi and N . edax, they are attached and inconspicuous in Kuphus polythalamia, Bactronophorus thoracites, Neoteredo reynei, Dicyathifer manni, Teredothyra matocotana, T . dominicensis, Psiloteredo healdi, P. senegalensis, Teredo furcifera, T . fulleri, T .
clappi, T . navalis, T . poculifer, Lyrodus massa, L. pedicellatus, L.
takanoshimensis, L. mediolobata, Spathoteredo spatha, X. obtusa,
Nausitora fusticula, N . hedleyi, N . dunlopei, Bankia gouldi, B. indica,
B. australis, B. setacea and B. campanellata.
Though shipworms have the basic palp structure of an outer and
inner pair, these structures vary considerably in size and efficiency. In
all species hitherto studied the outer and inner palps may be recognized.
Variations in the relative proportions of these are to be attributed to
habitat specializations and to the degree of dependence on planktonic
food. The palps of Teredo norvegica (Nototeredo norvagica) are by far
the most conspicuous and perhaps capable of quantitative selection
(Purchon, 1941). That the nature of the palps in the Teredinidae has
an evolutionary significance is evident because all the genera known to
possess free and distinct labial palps are comparatively less evolved
than those genera with reduced palps. A trend towards reduction in
functional efficiency is evident during the course of evolution where a
noticeable shift from dominant plankton feeding towards dominant
cellulose feeding has taken place with associated adjustments in structure and physiology.
In the digestive system, the organs which show noticeable variations are the stomach, caecum and intestine. Moreover, the anal canal
may be open or closed. The stomach is globular in genera such as
KzLphus, Bactronophorus, Neoteredo, Dicyathifer, Teredothyra, Uperotus,
Psiloteredo and Nototeredo ; is elongate-globular in Teredora and elongate
in Teredo, Lyrodus, Nausitora and Bankia. Five evaginations of the
stomach have been reported for Teredo navalis, Bankia indica and
Nausitora hedleyi. These are the style sac, the lateral pouch (=left
pouch of Purchon, 1960), the dorsal caecum (=dorsal hood of Purchon),
the digestive diverticula and the caecum (=appendix of Purchon). The
stomach in the above is assignable to type V (Purchon 1960).
By far the most conspicuous part of the gut is the caecum (appendix)
which extends horizontally backwards. It is absent in the genus
Kuphus, is small in Dicyathifer, Teredothyra matocotana and Nototeredo
knoxi, moderately large in Bactronophorus, Teredothyra dominieensis,
369
gouldi (Bartsch), B. setacea (Tryon) and B. carinata (Gray), variations
exist in different genera.
While the labial palps are free and distinguishable in Teredora
princesae, T . malleolus, Uperotus clavus, U. rehderi, Psiloteredo megotara,
Nototeredo norvagica, N . knoxi and N . edax, they are attached and inconspicuous in Kuphus polythalamia, Bactronophorus thoracites, Neoteredo reynei, Dicyathifer manni, Teredothyra matocotana, T . dominicensis, Psiloteredo healdi, P. senegalensis, Teredo furcifera, T . fulleri, T .
clappi, T . navalis, T . poculifer, Lyrodus massa, L. pedicellatus, L.
takanoshimensis, L. mediolobata, Spathoteredo spatha, X. obtusa,
Nausitora fusticula, N . hedleyi, N . dunlopei, Bankia gouldi, B. indica,
B. australis, B. setacea and B. campanellata.
Though shipworms have the basic palp structure of an outer and
inner pair, these structures vary considerably in size and efficiency. In
all species hitherto studied the outer and inner palps may be recognized.
Variations in the relative proportions of these are to be attributed to
habitat specializations and to the degree of dependence on planktonic
food. The palps of Teredo norvegica (Nototeredo norvagica) are by far
the most conspicuous and perhaps capable of quantitative selection
(Purchon, 1941). That the nature of the palps in the Teredinidae has
an evolutionary significance is evident because all the genera known to
possess free and distinct labial palps are comparatively less evolved
than those genera with reduced palps. A trend towards reduction in
functional efficiency is evident during the course of evolution where a
noticeable shift from dominant plankton feeding towards dominant
cellulose feeding has taken place with associated adjustments in structure and physiology.
In the digestive system, the organs which show noticeable variations are the stomach, caecum and intestine. Moreover, the anal canal
may be open or closed. The stomach is globular in genera such as
KzLphus, Bactronophorus, Neoteredo, Dicyathifer, Teredothyra, Uperotus,
Psiloteredo and Nototeredo ; is elongate-globular in Teredora and elongate
in Teredo, Lyrodus, Nausitora and Bankia. Five evaginations of the
stomach have been reported for Teredo navalis, Bankia indica and
Nausitora hedleyi. These are the style sac, the lateral pouch (=left
pouch of Purchon, 1960), the dorsal caecum (=dorsal hood of Purchon),
the digestive diverticula and the caecum (=appendix of Purchon). The
stomach in the above is assignable to type V (Purchon 1960).
By far the most conspicuous part of the gut is the caecum (appendix)
which extends horizontally backwards. It is absent in the genus
Kuphus, is small in Dicyathifer, Teredothyra matocotana and Nototeredo
knoxi, moderately large in Bactronophorus, Teredothyra dominieensis,