Podocoryna tenuis (Hydrozoa) in temperate waters of the southwestern Atlantic: additional data on life cycle stages support its synonym with Podocoryna humilis

Abstract

Two species of Hydractiniidae (Hydrozoa) with metagenetic life cycle have been recorded for the temperate region of the southwestern Atlantic Ocean: the medusa stage of Podocoryna tenuis and the polyp stage of P. humilis. Both the adult medusa of P. humilis and the polyp stage of P. tenuis are unknown, but it is possible that they are different stages of the same species, a hypothesis still to be tested. Colonies of P. humilis growing on the southern king crab Lithodes santolla collected at the Atlantic Patagonian coast, and two small medusae released from these hydroid colonies were analyzed. Medusa of P. humilis were kept alive for 3 days and they were morphologically compared with the medusae of P. tenuis sorted out from ~ 2,500 plankton samples along the Atlantic Patagonian coast. The study of these specimens allowed reassessing the taxonomic status of P. humilis and P. tenuis from the southwestern Atlantic Ocean. Polyp and young medusa stages of P. humilis were described, and additional information was recovered to better describe the medusa stage of P. tenuis. New morphologic and biogeographic evidences in order to propose the synonymy between P. tenuis and P. humilis were discussed.