Abstract

Elysia diomedea presents morphological variation (e.g. adult size, color) across its geographical distribution in Ecuador. Because of the reported morphological variation and absence of genetic information for this species in Ecuador, we first analyzed mtDNA sequences in three populations (Ballenita, La Cabuya, and Mompiche). We confirmed that individuals from the three locations belonged to E. diomedea and that there was no population structure that could explain their morphological differences. Next, we analyzed general aspects about the reproductive biology and embryology of this species. Live slugs from the Ballenita population were maintained and reproduced ex situ. Egg ribbons and embryos were fixed and observed by brightfield and confocal microscopy. We observed a single embryo per capsule, 98 embryos per mm2 of egg ribbon, and compared the cleavage pattern of this species to other heterobranchs and spiralians. E. diomedea early development was characterized by a slight unequal first cleavage, occurrence of a 3-cell stage in the second cleavage, and the formation of an enlarged second quartet of micromeres. We observed the presence of extra zygotic yolk bodies in the early embryos of some egg ribbons. Both reproductive and embryological characteristics, such as presence of stomodeum in the larva, and ingestion of particles after hatching confirmed the planktotrophic veliger larvae of this species, which differed from a majority of saccoglossans.