Diego Gabriel Zelaya

New species of Thyasira , Mendicula, and Axinulus (Bivalvia, Thyasiroidea) from Sub-Antarctic and Antarctic waters

Three new thyasirid species from the Sub-Antarctic and Antarctic waters are described: Thyasira patagonica, Mendicula sudamericana, and Axinulus antarcticus. T. patagonica is characterized by its strong commarginal sculpture, shell as height as length or higher than long, posterior auricle delimited by a deep submarginal sulcus, and a long and sloping straight anterior half of dorsal margin. M. sudamericana distinguished by its longer than high shell outline, elongated tooth-like enlargement anterior to beak, gills with only one demibranch at each side, and foot with a marked heel. A. antarcticus has a minute, subquadrate shell, hinge with a small swelling anterior to beak, gills with a single demibranch, and the lateral body pouch elongated and almost smooth. The present study provides the first reliable record of thyasirids, with a single demibranch from the Southern Ocean. Moreover, characters for a better definition of Mendicula are provided.

Two new trochids of the genus Antimargarita (Gastropoda: Vetigastropoda: Trochidae) from the Bellingshausen Sea and South Shetland Islands, Antarctica

Two new trochids of the genus Antimargarita, A. powelli and A. bentarti, from the Antarctic waters are described here. A. powelli, from the Bellingshausen Sea, is distinguished by its rounded whorls, numerous spiral cords, a radula with seven lateral teeth at each side of the rachidian, and an epipodium with eight pairs of tentacles. A. bentarti, from the South Shetland Islands, is characterized by having a shell outline gradated by prominent primary spiral cords, a radula with five lateral teeth at each side of the rachidian and an epipodium with six tentacles on the left side. The diagnostic features for Antimargarita are redefined considering both shell and anatomical features and its suprageneric placement is discussed.

Marine Bivalves from the Argentine Coast and Continental Shelf: Species Diversity and Assessment of the Historical Knowledge *

Abstract: Bivalves are one of the most abundant groups of invertebrates in many benthic communities. From 1817 to date, numerous contributions have dealt with the Argentine fauna of marine bivalves. Despite this, at present, there is no a text summarizing the currently available information on this group in Argentine waters. The present contribution aims to provide a synthesis of the current state of knowledge of systematics, geographic distribution, biology, and ecology of the living marine and estuarine species of bivalves from the Argentine coast and its shelf and, based on this information, to analyze the species diversity of these areas. For that, 225 publications, including results of scientific expeditions, systematic revisions, description of new species, new distributional records, checklists, compilations on the diversity for particular areas, and contributions dealing with biological and ecological information, were surveyed. As part of this study, 277 nominal species of bivalves were found reported for the study area, although only 169 of them are currently regarded as valid. The analysis of the available bibliography makes evident that the Argentine bivalves have been overlooked throughout the years. This fact results in several limitations and gaps in the current knowledge of this fauna, which are highlighted in the present revision.