New morphological data on a sub-Antarctic acanthocephalan, Aspersentis johni (Baylis, 1929) (Palaeacanthocephala: Heteracanthocephalidae).

Aspersentis johni (Baylis, 1929) (Acanthocephala: Heteracanthocephalidae) is redescribed based on specimens collected from a sub-Antarctic nototheniid fish, Patagonotothen longipes. Hosts were caught in the Beagle Channel (Magellanic subregion). The redescription incorporates previously undescribed or poorly described features and complete measurements. Acanthocephalans of the genus Aspersentis have a strong dorso-ventrally asymmetrical armament of the proboscis (ventral hooks are much larger than dorsal), the presence of conspicuous spines on the anterior part of the trunk and smaller spines occurring more posteriorly and reaching the extremity of the body, and narrow lemnisci longer than the proboscis receptacle. Features useful to distinguish A. johni from A. megarhynchus (Linstow, 1892) are: 10-13 proboscis hooks in each row, the maximum length of the ventral hooks 77-108 microm, a narrower proboscis with a length/width ratio of 2.16-3.22:1 (mean 2.78:1), an egg length of 87-102 microm, and an unusual form of the posterior extremity of females (the presence of a terminal concavity between two lateral lobes).