Early development of two species of Spirobranchus Blainville, 1818 (Polychaeta: Serpulidae) from the Southern Mexican Pacific

Species of the genus Spirobranchus are sessile polychaetes with an important role in marine ecosystems since they are suspension-feeding invertebrates. However, for most species almost nothing is known about their early and larval development, so we describe the early development of two species of Spirobranchus from the Southern Mexican Pacific. The early trochophore larva of S. incrassatus was formed 12 h post-fertilization at 28 degrees C and was described up to a 24-day-old metamorph, whilst it was only possible to follow S. cf. corniculatus to the eight-day-old early trochophore larva. With this study, we describe the early embryological stages, which provide an understanding of the reproductive biology of these polychaetes. Furthermore, this type of information is the basis for future experimental work on the possible response of embryos and larvae to changes in environmental variables, such as temperature.