Organisation of the praesoma in Acanthocephalus anguillae (Acanthocephala,Palaeacanthocephala) with special reference to the muscular system

The or,organisation of the praesoma in the parasite Acanthocephalus anguill ae was studied on the light and electron microscopic level, with emphasis o n the morphology of the musculature. The study was compiled to add new data to the ground pattern of the Acanthocephala for analysis of the phylogenet ic relationships within the Gnathifera. In A, anguillae the praesomal epide rmis and lemnisci form a coherent syncytium, separated from the epidermis o f the trunk. Hooks are seen to be derivatives of the subepidermal basal lam ina and are covered by the praesomal epidermis. The praesomal circular body wall musculature forms a network of anastomosing muscle fibres that lines the proboscis; a praesomal longitudinal body wall musculature does not exis t. The truncal circular and longitudinal body wall musculature rise up to t he praesomal proboscis. The unpaired proboscis retractor, consisting of lon gitudinal circomyar fibres, forms an outer and an inner concentric tube; th e latter extends through the entire praesoma and penetrates the receptacle wall. The sack-like receptacle is surrounded by a receptacle constrictor. T he nervous system of the praesoma consists of a prominent cerebral ganglion , three nerves which extend anteriorly, ramify and end within the praesomal musculature, and two strong lateral posterior nerves. A, anguillae lacks a n apical organ, lateral organs and a support cell. Many of the features pre sent in the praesoma of A, anguillae can be assumed as ground-pattern chara cteristics of the Acanthocephala.