CONICET | Buscador de Institutos y Recursos Humanos

Embryo morphology, feeding mechanism and changes in composition of the egg capsule content duringdevelopment (intracapsular fluids and embryos) were studied in Odontocymbiola magellanica fromnewly spawned egg capsules to the pre-hatching juvenile stage. Changes in embryo morphology andbehavior are presented, based on observations and micrographs of living specimens and scanning electronmicroscopy. The arrangement of velar cilia and athrocytes and shell gland location and developmentdiffered markedly from other studied caenogastropods. Embryo ingestion of intracapsular fluid was promotedby velar ciliary currents at least from the early veliger stage, while feeding by grazing on the innermembranous layer of the egg capsule was rarely observed until juveniles were about to hatch. The maingrowth of embryos occurred during the veliger stages. A significant nutritional investment in egg capsules,as compared with other South American volutids was observed. Nutrition from proteins seemed topredominate at the expense of a high molecular weight fraction (>220 kDa). Calcium concentration in theintracapsular fluid remained constant during development, but notably, the total intracapsular content(i.e., the amount contained in both fluid and embryos) increased 3-fold, whichmaybe explained by extractionfrom the egg capsule magnesium-rich calcite cover, or alternatively, by uptake of calcium from thesurrounding sea water. Ammonia, a major end-product of nitrogen metabolism in marine invertebrates,was present in both embryos and intracapsular fluid, from which it may easily diffuse to the surroundingsea water through the egg capsule wall. Our results on embryo morphology, development and biochemicalchanges provide useful comparative data for evolutionary and developmental studies in the Volutidaeas well as in other caenogastropods.