Neural extract induction of egg-laying and subsequent embryological development in hard and soft egg capsules of the marine snail, Chorus giganteus

The great abundance, long evolutionary history, and diversity of gastropods make this class of mollusks interesting for studies of the evolution and m echanisms of reproductive adaptations. This study investigated induction of laying of egg capsules and subsequent intracapsular embryonic development of the Chilean muricid snail Chorus giganteus, whose natural population has suffered a serious decline during the last 20 years. Central nervous syste m (CNS) extracts (supernatants of homogenates of combined circumesophageal, pedal, and buccal ganglia that were boiled and centrifuged) caused the lay ing of both soft bulb-shaped capsules and hard well-formed capsules. Latenc y between injection and capsule laying was 3-6 h. Neither control injection s of vehicle (filtered sea water) nor injection of extracts containing less than half of a CNS per recipient caused laying. All but two of 36 capsules laid in response to extract injection contained eggs. Eggs in soft capsule s developed normally initially but were subject to infections; although egg s in some hard capsules showed arrested development, in others development appeared to proceed normally, and veliger larvae developed in one hard caps ule that was maintained for 49 days. The capsule wails: of induced hard cap sules had a similar multilayered microscopic structure to spontaneously lai d capsules. Soft capsules had a less compact middle lamina with missing or much less compact outer lamina. These experiments demonstrate the presence of a putative hormone activating egg laying in nervous system extracts of C . giganteus and demonstrate that normal intracapsular development can occur in some of the resultant capsules.