Additional morphological information on Oculotrema hippopotami Stunkard, 1924 (Monogenea: Polystomatidae) parasitic on the African hippopotamus

Abstract

Oculotrema hippopotami Stunkard, 1924, is the only monogenean known from a homoiotherm host, namely the African hippopotamus (Hippopotamus amphibius Linnaeus, 1758). The original description was based on five shrunken, unflattened specimens. Initially O. hippopotami was not widely accepted as a valid species and the existence of this parasite was only confirmed four decades later. New specimens of O. hippopotami were collected during a hippopotamus culling operation in the KwaZulu Natal Province of South Africa. Examination of these specimens confirmed most of Stunkard’s description and revealed the presence of a bucco oesophageal canal, a uterine evagination, an operculated egg, the retention of marginal hooklets in the mature parasite and the ability to double its length and feed over a large area around its position of attachment. This study also reveals striking similarities with Concinnocotyla, the polystome of the Australian lungfish, and chelonian polystomes.  Morphological parameters of the species are redefined. A maximum of 24 parasites was found on a single eye and a maximum of 37 on an individual host specimen. Prevalence was found to be 75% for mature parasites, 85% for immature specimens and 90% for the total sample.

Key words: Platyhelminthes, Monogenea, Polystomatidae, morphology,  hippopotamus.