engleski

Mineral Components in the Opisthobranch Gastropod Shell Aplysia spp.

One of the characteristics of marine gastropods is a spiral shell in the larval life phase which completely encloses and protects the specimen's soft tissue. As distinguished from the majority of other species the Opisthobranch group, in adult life, have solid shells that are more or less reduced. After veliger metamorphosis the shell may develop into a complete shell (Cephalaspidea), a reduced form of simple shell (Anaspidea) or may completely disappear in adult specimens (Nudibranchia). Herein, the crystal structure and phase composition of larval and adult shells of two sea hare species Aplysia spp. were analysed by X-ray diffraction. Diffraction patterns of A. punctata embryos show that the very first aragonite minerals appear 12 days after egg-strings deposition. Fully formed aragonite crystals were recorded in more developed embryos even before hatching (23 days). Veligers have the first shell made of aragonite and interestingly the operculum is also calcified. Morphologically reduced adult shells consist of two organic layers between which is inserted a calcified layer comprising of aragonite (71 M %) and feldspar (19 M %). The first traces of mineralisation within the related species A. fasciata do not appear until 14 days after egg-strings deposition. The adult shell was found to consist only of aragonite crystals.

mineral composition; Opisthobrancia shell; Aplysia spp.; aragonite; feldspar; X-ray diffraction

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