| Abstract: | The cuticle of Proneomenia consists of a mucoid matrix containing calcareous spicules and is secreted by the mantle epithelium at the base of the ventral (pedal) groove and over the general body surface. Histochemical examination shows the matrix to be composed of a glycoprotein complex with high acid mucopolysaccharide and low protein contents in which tanning plays little part in stabilization.
The cuticle of the Aplacophora is tentatively equated with an early mucoid stage in the evolution of the molluscan shell and it is suggested that secretion of additional protein, followed by hardening by quinone-tanning, are necessary further stages before a calcified shell evolves. The aplacophoran cuticle is compared with that of Acanthochitona (Polyplacophora) and, although they are similar in many respects, the latter has in addition a discrete inner cuticular layer whichmay act as a semi-conducting membrane in the deposition of the calcareous plates. The spicules are similar in both groups, each being secreted within a thin cup-like membrane which exhibits somewhat similar properties to the inner cuticle. |
