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SETTLEMENT,
METAMORPHOSIS AND HARD TISSUE FORMATION IN
CHITONS
Members
of the class Polyplacophora are a small group of marine mollusks
found in a wide range of habitats in both temperate and tropical
regions. Some species are found at great depth. Despite many
investigations, very little is known of their early life
histories. More information is required on the larval growth,
settlement, metamorphosis and mineralization of hard tissues
such as valve (shell-plate), radular teeth and scale.
The chitons, Acanthopleura
japonica and Acanthochitona
achates are abundant in the intertidal zones along rocky
coasts of Japan. Using these species, I attempted to induce
spawning and larval settlement and metamorphosis.
The periostracum of the mussel, Septifer
virgatus induced settlement and metamorphosis in A.
japonica. L-DOPA and DL-DOPA induced settlement but not
metamorphosis.
Valve formation and calcification appear to begin at
metamorphosis. The juvenile at less than one day from
metamorphosing had seven valves both in A. japonica and in A. achates.
Radula
sac appears in free-swimming larva. The accumulation of iron was
observed in the central part of the larvae. It is suggested that
iron mineralization had been occur during larval stage. The
radular teeth of A.
japonica undergo a morphological change during their
ontogeny. The adult of A. japonica had two mono-cuspid major lateral teeth per row, the
juvenile just after metamorphosing from larva had two-cuspid
lateral tooth. Whereas the change from juvenile to adult tooth
was not observed in A.
achates. Ontogenetic change in morphology of radular teeth
may occur in those species in which there is a marked change in
the diet between juveniles and the adult. |
