Encapsulated development of the marine prosobranch gastropod Nucella lapillus

Nucella (=Thais) lapillus (L.) develops to the juvenile stage within an egg capsule. This study was undertaken to investigate nutritive and bacteriostatic properties of the intracapsular fluid for this species. Capsules were collected intertidally at Nahant, Massachusetts, USA, in the summers of 1982 and 1983. The average capsule contained only 1.1 l of intracapsular fluid per embryo. A statistically significant correlation was observed between capsule height and number of developing embryos contained therein, although the number of embryos per capsule was more closely related to capsule volume. Total dry weight of encapsulated, shelled embryos increased exponentially as a function of shell length. However, weight increases may be entirely due to shell calcification; the average dry tissue weight of shelled embryos was significantly below that for pre-shelled individuals, suggesting a net loss of biomass during development. Aliquots of intracapsular fluid failed to inhibit the growth of the 13 bacterial strains tested. Despite the above results, pre-shelled embryos generally survived only several days following their premature removal from egg capsules at 12°C. Shelled veligers were reared outside of the capsules with no apparent ill effects. An explanation for these survivorship results is elusive.