Size-depth patterns in two bathyal turrid gastropods: Benthomangelia antonia (Dall) and Oenopota ovalis (Friele)

During the past decade, there has been a resurgence of interest in the evol utionary and ecological significance of animal body size. Geographic patter ns of body size in deep-sea organisms remain poorly described. In this pape r, we analyze depth-related trends of larval and adult shell size in two tu rrids (Gastropoda) from the western North Atlantic. The upper bathyal Oenop ota ovalis (478-2022 m), which has non-planktotrophic development, shows si gnificant positive size-depth dines for larval, but not adult shells. The l ower bathyal Benthomangelia antonia (2359-3834 m), with planktotrophic deve lopment, shows no trend for larval shells, but a positive relationship of s ize to depth for adult shells. The increase in size with depth confirms ear lier observations of size-depth dines in deep-sea snails, which may reflect selection for greater competitive ability and foraging efficiency with inc reased depth. Contrasts in clinal variation between larval and adult shells suggest that different stages of life history in deep-sea snails may respo nd independently to environmental gradients.