Agradecimentos: The field-observation-based project was originally conceptualized by the late Professor Walter Narchi and executed by the late Professor Osmar Domaneschi, who served as an excellent mentor for two of the current authors (F.D.P. and A.S.). We also acknowledge the divers Tânia Brito and Luciano Candisani from the Oceanographic Institute of the University of São Paulo (IOUSP) for underwater observations. We greatly appreciate the constructive input by Robert Prezant, John Taylor, and an anonymous colleague during the review process. This work was carried out within the Brazilian Antarctic Programme (PROANTAR), with financial and logistic support provided by the National Council of Scientific and Technological Development (CNPq), the Brazilian Navy and Brazilian Air Force. It was also supported by scholarships from São Paulo Research Foundation (FAPESP) (Proc. 99/02399-9) and from "Pós-Graduação, Área Zoologia, IBUSP". FAPESP also provided financial support through grants no. 2018/06347-6 and 2018/10313-0. Relevant bivalve research at the Field Museum was supported by U.S. National Science Foundation (NSF) award DEB-0732854 to Rüdiger Bieler for the Bivalve-Tree-of-Life (BivAToL) project. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript Ver menos

Abstract: Laternula elliptica (P. P. King, 1832) is the sole representative of the anomalodesmatan family Laternulidae and the largest bivalve in the Antarctic and Subantarctic. A keystone species of the regional benthic communities, it has reached model status, having been studied in hundreds of scientific works across many biological disciplines. In contrast, its anatomy has remained poorly known, with prior published data limited to partial descriptions based on chemically preserved specimens. Based on observations of aquarium-maintained living animals at the Brazilian Comandante Ferraz Antarctic Station, gross-morphological dissections, and histological sectioning, the comparative anatomy, functional morphology, and aspects of behavior of L. elliptica are described and discussed. Special focus is placed on the pallial organs (including elucidation of cleansing and feeding sorting mechanisms in the mantle cavity) and the musculature. Among the noteworthy findings are the presence of well-developed siphons furnished with sensory tentacles at its tips, some of which bearing eyes; large, folded gills and labial palps capable of sorting the material entering the mantle cavity; an inter-chamber communication in the posterior region of the mantle cavity; an ample ventral mantle fusion with an anterior pedal gape; the absence of a 4th pallial opening; and the absence of a ligamental lithodesma in adult specimens. This study reevaluates the available anatomical data in the literature, both supplementing and correcting previously published accounts Ver menos