Reproductive seasonality, oviposition and development of the nassariid whelk Buccinanops cochlidium (Dillwyn, 1817) in Patagonia, Argentina

Abstract

Seasonality of reproduction in Buccinanops cochlidium, including mating, oviposition and embryonic development, was studied within a population in Patagonia. Mating was observed mainly during autumn and winter (March to October). Females carrying egg capsules were found between July and October when water temperature was 10°C, while development of embryos continued until February (the hatching peak) when water temperature was 18°C. All egg capsule masses were found attached to the shells of females 80–102 mm in length. The spawn consisted of 80 to 238 egg capsules, attached to the apertural callus of the shell. Linear regression analysis showed no significant relationship between female size and number of egg capsules. Each egg capsule contained 3100 eggs on average, with a mean egg diameter before cleavage of 227.5 µm. One to 20 embryos completed their development within each egg capsule by ingesting around 570 nurse eggs. The embryos followed a typical holoblastic spiralian division until gastrulation. During the ‘veliger’ stage the embryo consumed nurse eggs and formed a large rounded embryo up to 2 mm in diameter. After shell development the embryos hatched as crawling juveniles of 4.0 mm shell length through an opening opposite to the capsule stalk. There was an inverse relationship between the mean hatching shell size and the number of embryos per egg capsule. Under laboratory conditions development was completed in four months.