Morphology and ultrastructure of the anterior end of Diplocirrus longisetosus Marenzeller, 1890 (Flabelligeridae, Polychaeta, Annelida)

Abstract

The morphology and ultrastructure of the sedentary polychaete Diplocirrus longisetosus Marenzeller, 1890, collected from the White Sea, were studied using dissection, histological methods, light microscopy, and both scanning and transmission electron microscopy. The prostomium and peristomium carry a pair of palps, eight branchiae, a pair of nuchal organs and two nephridiopores, ciliated folds and the mouth. The prostomium, peristomium and the first chaetigerous segment with all appendages comprise the so-called siphon complex. The mouth leads to a pharyngeal organ that is closed ventrally and composed of a ventral muscle bulb adjoined dorsally by two folds projecting into the pharyngeal lumen. These parts are connected and enveloped by the longitudinal investing muscle. No tongue-like organ is present. The nervous system of the siphonal part comprises the brain, the circum-oesophageal connectives and the ganglia of the peristomium and first chaetigerous segment.