Reproductive seasonality, oviposition and embryological development of the nassariid whelk Buccinanops cochlidium (Dillwyn, 1817) in Golfo San José (Patagonia, Argentina).

AVERBUJ A.; PENCHASZADEH, P. E.

JOURNAL OF MOLLUSCAN STUDIES

OXFORD UNIV PRESS

Año: 2010 vol. 76 p. 25 - 32

0260-1230

A study to describe the seasonality of reproduction in Buccinanops cochlidium, including mating, oviposition and embryonic development, was conducted within a population inhabiting Patagonian waters. Mating individuals were observed mainly during Autumn and Winter (March to October, in the Southern Hemisphere). Living sperm was found in the bursa copulatrix of the females in the same months that mating was observed. Females carrying egg capsules were found between July and October (with October having the highest frequency) when water temperature was 10 ºC, while the development of the embryos continued until February (the hatching peak) when water temperature was 18 ºC. All the egg capsule masses were found attached to the shells of female snails that measured between 80 and 102 mm in length. The spawn consisted of 80 to 238 egg capsules, attached to the callus region of the shell. Linear regression analysis showed no significant relationship of the female size to the number of egg capsules. Each egg capsule contained 3,100 eggs on average; with a mean egg diameter before cleavage of 227.5 µm. One to 20 embryos completed their development within the egg capsule by ingesting around 570 nurse eggs, which are swallowed whole. The embryos followed a typical holoblastic spiralian division until gastrulation. At the ?veliger? stage the embryo consumed as many nurse eggs as possible, forming a large rounded embryo up to 2 mm in diameter. After completing the development of the shell the embryos hatched as crawling juveniles through an opening area opposed to the capsule?s stalk, with a mean shell length of the hatchlings of 4.0 mm. The inverse relationship between the mean hatching shell size and the number of embryos per egg capsule was explained by a linear regression. In laboratory conditioned aquaria the embryos completed development in four months.