Abstract

Early life stages of three co-occurring whelks from New Zealand waters, the buccinids Cominella virgata, C. maculosa and the muricid Haustrum scobina, were studied in order to compare their oviposition patterns, capsule morphology and intra-capsular traits. Duration of intra-capsular development was similar among species (i.e. 10 weeks until hatching); nonetheless, differences in provisioning and allocation were observed. Cominella virgata (1 embryo per capsule) and C. maculosa (7.7 +/- 0.2 embryos per capsule) provided their embryos with a jelly-like albumen matrix and all of embryos within the capsule developed. Haustrum scobina encapsulated 235 +/- 17 embryos per capsule but only 10 on average reached the hatching stage, with the remaining siblings being consumed as nurse embryos during development (i.e. morula stage). Hatchling morphology and mean size varied among species: C. virgata had a 'double whorled' shell of 2.7 mm length (SL), whereas C. maculosa and H. scobina had 'single whorled' shells of 1.6 mm and 1.2 mm SL, respectively. Trade-offs between size at hatching and hatchling number also occurred in the latter two species. Inter-specific differences in capsular and juvenile traits described here are likely to have major ecological consequences during the early life history stages of these co-occurring direct-developing snails.