Fig. 5

Elements of the alimentary and digestive system in Alviniconcha. Micrographs depict: a the anatomy of the buccal cavity; b internal and external morphology of the alimentary canal including: i) upper posterior oesophagus (uPOe) – posterior to the osophageal nerve ring encircling the mid-oesophagus (NR + MOe) – with ventral folds clearly visible and ii) transverse incision of uPOe immediately prior to mid-posterior oesophageal juction (in iii and iv) with T-profile of ventral folds highlighted. In iii) the mid-posterior oesophageal junction is marked by a decrease in diameter and (iv) the emergence of numerous dorsal folds, which rapidly become established (v). In vi) the lower posterior oesophagus (POe) enters the visceral haemocoel and communicates with the stomach posteriorly: arrow indicates the direction of travel. A schematic overview of stomach (St) anatomy in presented in c including micrographs of several anatomical features; in d scanning electron micrographs of pristine posterior regions of radulae from each species are provided. Pictures in a-c are from a formalin-fixed A. kojimai specimen. Additional abbreviations: AA Anterior aorta; ADD Anterior digestive duct; AOe Anterior oesophagus; BM Buccal mass; CpV Cephalopedal Vein; CT Connective tissue; DF Dorsal fold; DG Digestive gland; GS Gastric shield; In Intestine; MaT Major typhosole; MiT Minor typhosole; Mo Mouth; OeP Oesophageal pouches; PDD Posterior digestive duct; R Radula; Re Rectum; SA Sorting area; SS Style sac