Localization of serotonin and fmrfamide in the bivalve molluscMytilis edulis at early stages of its development

Location and time of appearance of serotonin and FM RFamide in ontogenesis of the bivalve mollusc Mytilus adulis L. has been studied. Serotonin first appears at a transfer from the last trochophore stage to the early veliger stage, 30–32 h after fertilization and is detected in a large cell located immediately at the base of the apical plume. FMRFamide appears 14–15 h after fertilization, during the transfer from the conchostoma stage to the early trochophore stage before the turning out of the shell gland and is a marker of the future shell site. It is located as a transverse stretch on the back of the larva in the area of the future shell. After the turning out of the shell gland the stretch is markedly shortened, while its processes approach the larval surface and are located under the shell. A suggestion is made about a morphogenetic function of FMRFamide.