Comparative histopathology of Longicollum (Acanthocephala: Pomphorhynchidae) infection in the alimentary tract and spleen of Acanthopagrus australis (Pisces: Sparidae).

The pomphorhynchid acanthocephalan Longicollum alemniscus infected the rectum of 16 and the intestine of five of 628 Acanthopagrus australis from Moreton Bay, Queensland. The neck and proboscis penetrated the entire gut wall and were surrounded by a layer of compact, rounded fibroblasts inside a layer of elongated fibroblasts and scattered connective tissue fibres. These layers extended across the entire gut wall and into the capsule that enclosed the proboscis outside of the gut. A similar parasite occurred extraintestinally in three fish; the proboscis of one penetrated into the spleen. The spleen was shrunken, with the proboscis and anterior part of the neck enclosed in a capsule of proliferated connective tissue and cellular elements similar to that in the response to infection of the gut wall.