Ultrastructure and Function of the Anterior Feeding Apparatus in Labronema Sp

Abstract

Structure and function of the anterior feeding apparatus of Labronema sp., predominantly a predatory nematode, were studied by electronmicroscopic and cinematographic analysis. The ultrastructure of the anterior feeding apparatus is basically similar to that of Aporcelaimellus spp. In Labronema sp. each of the eight protractor muscles sends projections towards the body wall where they form branches that partly penetrate the somatic musculature and the nerve chords. Only one set of 4 retractor muscles is present. Odontostyle retraction may be supported by membrane-like structures between the 'hydrostatic cylinder' and the body wall which become stretched as the odontostyle is protracted. Odontostyle protrusion is accompanied by a compression of the 'hydrostatic cylinder' which allows the smooth folding of the guiding sheath into an anterior loop. During the actual ingestion process the odontostyle is fully protruded, and strong suction is exerted whenever the oesophageal muscles contract. At the beginning of each ingestion pause some of the food drawn in was seen to flow back again into the perforated prey. It will be shown, that, due to the arrangement of the cuticular thickenings, the lumen within the slender part of the oesophagus will never become completely closed upon relaxation of the muscles that dilate it.