Exploring the anatomy of Cossura pygodactylata Jones, 1956 (Annelida, Cossuridae) using micro-computed tomography, with special emphasis on gut architecture

Abstract

The anatomy of Cossura pygodactylata Jones, 1956 (Annelida; Cossuridae) is presented, based on the study of specimens collected during the BIOICE project in Icelandic waters and additional material from the White Sea. General gross external and internal anatomy were investigated by means of micro-computed tomography (micro-CT) and compared with results obtained with light microscopy histological sectioning (LMHS). Micro-CT revealed a highly regionalised gut, posterior to the pharyngeal cavity and oesophagus, divided in an anterior stomach and a posterior intestine with different morphologies. The stomach is in the thoracic region, dorsally positioned and divided in a short and narrow anterior part and a longer posterior one, with an increasing diameter towards its posterior end. Both stomach regions bear a dorsal infolding of tissue, along its inner wall, that resembles to the typhlosole of the Clitellata. The heart is dorsally located and contains a heart body above the hind stomach. The intestine is wider than the stomach, without dorsal infolding inside the lumen and filling most part of the internal body cavity. A transitional cup-shaped gut element connecting the stomach and the intestine could be observed at the level of the last thoracic segment. In general, the resolution of micro-CT images reflects reasonably well the main elements of gross external and internal anatomy of cossurids, and that of gut architecture in particular.