Spawning and development of the Patagonian cold-water microgastropod Eatoniella turricula Ponder and Worsfold 1994 (Caenogastropoda: Eatoniellidae)

Species of Eatoniellidae are typical members of shallow, cold waters of the Southern Hemisphere; however, very little is known about their biology. This work deals with the first description of spawns and developmental stages for the family. All samples were collected from Southern Argentina and were identified as Eatoniella turricula based on shell, opercular, and radular characters. Spawn is composed by a globose, thick-walled capsule with a single egg/embryo surrounded by nutritive liquid which allows direct development. E. turricula is a very small species, with limitation to the energy available for reproduction and inhabiting in cold water implying a low metabolic and growth rate. The species is expected to produce few eggs, thereby increasing the possibilities of survival by allocating available energy to generate an abundant food supply within a thick-walled capsule that provides strong protection. This strategy resulted comparable to other microgastropods from cold water suggesting that evolved many times independently and convergently. The distribution of Eatoniellidae is also discussed considering its direct development as well as the geographical changes occurred in Southern areas during the last 20 millions of years, including the ongoing development of the Antarctic Circumpolar Current.