362
N. BALAKRISHNAN NAIR AND M. SARASWATHY
like shipworm. Teredora and Uperotus are very closely related, with
Uperotus probably the more primitive. Teredothyra, Bactronophorus,
Neoteredo and Dicyathifer are related and all might have evolved from
Teredora-like forms having simple pallets. Bactronophorus and
Neoteredo are highly specialized and probably have not given rise to any
other group. Some species of Teredo with single cupped pallets might
have evolved from forms like Dicyathifer or from Psiloteredo and species
with double cupped pallets probably stemmed from Teredothyra.
Turner thus feels that Teredo as constituted by her is polyphyletic in
origin evolved from Teredothyra, Dicyathifer and Teredora. Lyrodus
represents the most highly evolved group in the non-segmented pallet
line and has stemmed from Teredothyra.
Information on the nature of growth of the pallet is helpful in many
ways. It throws light on the nature of development of the different
elements that compose this structure and may provide clues for evolutionary trends. It may assist in the correct identification of species
since recent studies have shown that there may be noticeable changes
in the shape of the pallet as a result of age. For example Rancurel
(1955) has shown that the young pallets of Teredora malleolus (Turton)
have double tubes and may easily be confused with those of species in
Teredothyra and with Teredo fulleri Clapp. Close examination of the
entire stages of development of the pallet in Teredora malleolus reveal
the gradual broadening of the blade of the pallet and reduction of the
diameter of the tubes consequent on the thickening of the base. The
pallet of the adult specimens apparently does not show any sign of the
double tubes. A similar condition has been illustrated by Turner (1966)
in the same species from Bastia, Corsica. Again in Bankia carinata
(Gray) Turner has shown that the young pallets are Lyrodus-like and
could easily be confused with that genus. Monod’s studies (1952) on
the pallets of Teredo ( Psiloteredo) senegalensis Blainville have shown
that petitii Recluz is just the juvenile stage and the ecotypical form of
senegalensis. Certain growth stages of Teredo trulliformis Miller (Teredo
clappi Bartsch) has been illustrated by Edmondson (1942). The young
stages of this form resemble those of young fulleri.
The growth of the pallets is influenced either by the addition of
material over the entire surface and the extension of the blade laterally
and distally, (Teredo, Psiloteredo, Neoteredo, Teredora, Dicyathifer and
Kuphus) or by the addition of segments, the oldest being the smallest.
New cones are slightly larger than the one that precedes giving rise to a
plume-shaped pallet as in Bankia, Nausitora, Spathoteredo or Nototeredo. In these forms the stalk is continued to the very end of the
blade, but growth takes place only at the proximal part of the pallet.
N. BALAKRISHNAN NAIR AND M. SARASWATHY
like shipworm. Teredora and Uperotus are very closely related, with
Uperotus probably the more primitive. Teredothyra, Bactronophorus,
Neoteredo and Dicyathifer are related and all might have evolved from
Teredora-like forms having simple pallets. Bactronophorus and
Neoteredo are highly specialized and probably have not given rise to any
other group. Some species of Teredo with single cupped pallets might
have evolved from forms like Dicyathifer or from Psiloteredo and species
with double cupped pallets probably stemmed from Teredothyra.
Turner thus feels that Teredo as constituted by her is polyphyletic in
origin evolved from Teredothyra, Dicyathifer and Teredora. Lyrodus
represents the most highly evolved group in the non-segmented pallet
line and has stemmed from Teredothyra.
Information on the nature of growth of the pallet is helpful in many
ways. It throws light on the nature of development of the different
elements that compose this structure and may provide clues for evolutionary trends. It may assist in the correct identification of species
since recent studies have shown that there may be noticeable changes
in the shape of the pallet as a result of age. For example Rancurel
(1955) has shown that the young pallets of Teredora malleolus (Turton)
have double tubes and may easily be confused with those of species in
Teredothyra and with Teredo fulleri Clapp. Close examination of the
entire stages of development of the pallet in Teredora malleolus reveal
the gradual broadening of the blade of the pallet and reduction of the
diameter of the tubes consequent on the thickening of the base. The
pallet of the adult specimens apparently does not show any sign of the
double tubes. A similar condition has been illustrated by Turner (1966)
in the same species from Bastia, Corsica. Again in Bankia carinata
(Gray) Turner has shown that the young pallets are Lyrodus-like and
could easily be confused with that genus. Monod’s studies (1952) on
the pallets of Teredo ( Psiloteredo) senegalensis Blainville have shown
that petitii Recluz is just the juvenile stage and the ecotypical form of
senegalensis. Certain growth stages of Teredo trulliformis Miller (Teredo
clappi Bartsch) has been illustrated by Edmondson (1942). The young
stages of this form resemble those of young fulleri.
The growth of the pallets is influenced either by the addition of
material over the entire surface and the extension of the blade laterally
and distally, (Teredo, Psiloteredo, Neoteredo, Teredora, Dicyathifer and
Kuphus) or by the addition of segments, the oldest being the smallest.
New cones are slightly larger than the one that precedes giving rise to a
plume-shaped pallet as in Bankia, Nausitora, Spathoteredo or Nototeredo. In these forms the stalk is continued to the very end of the
blade, but growth takes place only at the proximal part of the pallet.