FIGURES 6A–G. Pisidium sterkianum, anatomy. A, B in Anatomical characteristics of two enigmatic and two poorly known Pisidium species (Bivalvia: Sphaeriidae) from Southern South America

FIGURES 6A–G. Pisidium sterkianum, anatomy. A, B. Arrangement of inner radial mantle and siphonal muscles. C. Distribution of scars of inner radial mantle muscles. D. Open nephridia, dorsal view. E. Closed nephridium, lateral view. F, G. Inner demibranchs, inner view, showing brood sac in an earlier (F) and advanced (G) stage of development. (al: ascending lamellae; as: anal siphon; bs: brood sac; dl: descending lamellae; dln: dorsal lobe of nephridium; e: embryo; irm: inner radial mantle muscles; irms: scars of inner radial mantle muscles; ll: lateral loop; pa: posterior adductor muscle; pd: pericardial duct; pl: pallial line; pss: pre-siphonal suture; sr1: anal siphon retractor; sr2: retractor muscles corresponding to lacking inhalant opening)