Development of the gastropod Trochita pileus (Calyptraeidae) in the sub-Antarctic Southwestern Atlantic

Abstract

The family Calyptraeidae is widely distributed around the world and shows several types of development all with physical care. Adults and broods of Trochita pileus from sub-Antarctic waters were collected during two cruises off Tierra del Fuego and Burdwood Bank at depths between 39 and 298 m. A total of 43 brooding females and 314 egg capsules of T. pileus were collected. Shell diameter of brooding females ranged from 12.6 to 28.8 mm. The egg capsules were flattened triangular sacs with rounded vertices and lateral margins longer than the distal margin. The number of egg capsules per brood increased significantly with increasing shell diameter of brooding females from 1 to 15 and a mean number of 7.9 ± 2.8. T. pileus has direct development from embryos which start consuming nurse eggs (oophagy) and then continue eating developing embryos (adelphophagy). The 80.7% of the initial eggs of T. pileus did not initiate development. From about 1000 initial uncleaved eggs per egg capsule (diameter around 250 µm), only 8 complete their development hatching as crawling juveniles. The observation of the post-gastrula stage of T. pileus swallowing all nurse eggs and latter also other embryos in the same stage of development is the first case of oophagy and adelphophagy in the genus Trochita. No late intracapsular cannibalism has been observed. To our knowledge, there are no records of Antarctic Calyptraeidae and this would be the development of one of the southernmost species described.