Some Species of the Genus Tetrancistrum Goto and Kikuchi, 1917 (Monogenoidea: Dactylogyridae)

Abstract

Species of Tetrancistrum from New Caledonian and Australian fishes are studied. Three new species are described. T. nasonis sp. n. from Naso annulatus differs from other species in the genus by the presence of an ejaculatory bulb, muscular projections in the wall of the copulation canal, and a copulatory organ consisting of a curved penis stylet with a curved accessory piece within the curve of the stylet. T. nebulosi sp. n. from Siganus nebulosus, Siganus oramin, and Siganus sp. differs from other species in the genus by the single rod-shaped accessory piece to the copulatory organ and the shape of the copulation canal. T. oraminii sp. n. from Siganus oramin differs from other species in the genus by the boomerang-shaped accessory piece to the copulatory organ with a recurved spine. T. fusiforme comb. n. is placed into this genus and a new record is made of its occurrence in Australia on Siganus lineatus and Acanthurus xanthopterus. Pseudohaliotrema longiphallus (MacCallum, 1915) comb. n. is removed into Pseudohaliotrema Yamaguti, 1953 and the genus Tetrancistrum is reviewed and its generic diagnosis emended. During an investigation into the monogenoid fauna of Australian fishes several species of Tetrancistrum Goto and Kikuchi, 1917 were found on the gills of members of the families Acanthuridae and Siganidae. Three of these were subsequently found to be new and the fourth was a new host and locality record. The present paper incorporates descriptions of these species together with a review and rediagnosis of the genus. All valid species so far described in Tetrancistrum are reported only from the Indo-Australasian fish fauna. Members of the Siganidae are the most numerous hosts and all species in this family except one are restricted to the Indo-Australasian area. Members of the Acanthuridae are the only other hosts reported to date, but the species concerned-Naso annulatus and Acanthurus xanthopterus-are restricted to the Indo-Pacific region. The only species of Tetrancistrum reported from a host not belonging to either of the above-mentioned families is T. lutiani Tubangui, 1931. This species was described on Lutjanus lioglossus from an aquarium which also contained species of the Acanthuridae and Siganidae and it is therefore unlikely that L. lioglossus was the natural host. The fish examined were collected by spearing or cast net. The specimens of Tetrancistrum were fixed flattened and unflattened in an AFA mixture and stained with hemalum. Received for publication 3 April 1967. * Present address. The addition of three new species to this genus has allowed a more explicit interpretation of the scope of the genus and the generic diagnosis is therefore emended accordingly. All measurements are in microns unless otherwise mentioned. Tetrancistrum generic diagnosis emend. Ancyrocephalinae Bychowsky, 1937 with characters of subfamily. Larval hooks all of same size; opisthaptoral transverse bars two, unarticulated, ventral bar smaller than dorsal. Hamuli two dissimilar pairs, roots with longitudinal striations, blades narrow, curved, much smaller than roots; dorsal hamuli with small ventral roots, large dorsal roots; ventral hamuli with almost equal roots, each root broad, massive, with nearly parallel sides. Gut bifurcate, crura united posteriorly, sometimes diverticulate laterally or ramified posteriorly. Testis circular, postovarian, perforated dorsoventrally; sperm duct not looping around gut crus; copulatory organ with sclerotized tubular penis stylet and one or more accessory pieces. Ovary dorsoventrally perforated, not looping around gut crus; copulation canal pore dextral. Type species: Tetrancistrum sigani Goto and Kikuchi, 1917. Included species: T. fusiforme (Yamaguti, 1953) comb. n., T. lutiani Tubangui, 1931, T. nasonis sp. n., T. nebulosi sp. n., T. oraminii sp. n.