Cystacanths of Acanthocephala in notothenioid fish from the Beagle Channel (sub-Antarctica).

The morphology of relaxed cystacanths of polymorphid acanthocephalans collected from notothenioid fishes in the Beagle Channel (Magellanic subregion of sub-Antarctica) is described. A parasite of birds, Andracantha baylisi (Zdzitowiecki, 1986), was found in Patagonotothen longipes and Champsocephalus esox. It has: a proboscis 0.82-0.89 mm long; a proboscis hook formula of 16 rows of 9/10-10/11, including 4-5 basal hooks; distal hooks with the longest blades; a fore-trunk not separated from the hind-trunk by a constriction; large somatic spines arranged in two zones separated by a zone of small, loosely dispersed spines; and only the anterior 36-40% of ventral side of the trunk is covered with spines. One male specimen of Corynosoma sp. was found in Patagonotothen tessellata. It differs from A. baylisi in that the distal proboscis hooks are similar in length to the prebasal hooks, it has a smaller proboscis (0.77 mm) and in the distribution of the somatic spines, which are contiguous with the genital spines on the ventral side of the trunk and lack a zone of small spines between zones of larger spines. A parasite of seals and fur seals, Corynosoma evae Zdzitowiecki, 1984, was found in P. longipes and Champsocephalus esox. It has: a proboscis 0.61-0.78 mm long; a proboscis hook formula of 20-22 rows of 12-13, including 3/4-4 basal hooks; prebasal hooks with the longest blades; a trunk divided into fore-trunk and hind-trunk; somatic spines covering the anterior 64-74% of the ventral side of the trunk; genital spines present only in males; and a terminal genital opening in both sexes. Corynosoma beaglense n. sp. was found in Champsocephalus esox. It has: an almost cylindrical proboscis (length 0.52-0.56 mm); a proboscis hook formula of 16 rows of 9/10-10/11, including 4-4/5 basal hooks; distal hooks shorter than the prebasal hooks; a fore-trunk not separated from the hind-trunk by a constriction; somatic spines contiguous with the genital spines on the ventral side of the trunk of the male and covering the entire length of the ventral side of the female trunk, and the presence of genital spines surrounding the terminal genital pore of the male. The definitive host of this species is unknown.