Nervous system development in feeding and nonfeeding asteroid larvae and the early juvenile

Larval and juvenile nervous systems (NS) of three asterinid sea stars with contrasting feeding and nonfeeding modes of development were characterized using the echinoderm-specific synaptotagmin antibody. In the feeding bipinnaria and brachiolaria larvae of Patiriella regularis, the species with ancestral-type development, an extensive NS was associated with the ciliary bands (CBs) and attachment complex. Lecithotrophic planktonic (Meridastra calcar) and benthic (Parvulastra exigua) brachiolariae lacked CBs and the associated NS, but had an extensive NS in the attachment complex. The similarity in the distribution and morphology of synaptotagmin immunoreactive neurons and the anatomy of the NS in the attachment complex of these closely related sea stars suggests conservation of neurogenesis in settlement-stage larvae regardless of larval feeding mode. Nerve cells were prominent on the brachia of all three species. In advanced brachiolariae the larval nervous system was localized to the adhesive disc as the larval body resorbed during metamorphosis. The structures and tissues that contained larval neurons degenerated during metamorphosis. There was no evidence that the larval NS persists through metamorphosis. In juvenile development, synaptotagmin IR was first evident in the NS of the tube feet. As the central nervous system developed, synaptotagmin IR reflected the histological organization of the adult NS. The juvenile NS formed de novo with a temporal lapse between histogenesis and synaptotagmin IR. We evaluated the ontogeny of NS organization in the change in body plan from the bilateral larva to the radial juvenile.