A review of the Tetrarhynchobothriidae Dollfus, 1969 (Cestoda: Trypanorhyncha) with descriptions of two new genera, Didymorhynchus and Zygorhynchus

Abstract

The Tetrarhynchobothriidae Dollfus, 1969 is considered a valid family and is amended to include three genera, Tetrarhynchobothrium Diesing, 1850, Didymorhynchus n. g. and Zygorhynchus n. g. The type-genus, Tetrarhynchobothrium, is distinguished by a scolex merging into the unsegmented neck region, by two internal seminal vesicles, a tetra-lobed ovary, a simple uterus, vitelline follicles encircling the medulla and the absence of a uterus with preformed diverticula or a uterine pore. Redescriptions of Tetrarhynchobothrium setiense Dollfus, 1969, T. rossii (Southwell, 1912) and T. unionifactor (Shipley & Hornell, 1904) are given. T. australe n. sp. is described from Myliobatis australis taken in South Australian waters. It is distinguished from congeners in having 8–9 hooks per half spiral row, hooks of uniform size, a longer scolex, a different scolex ratio, and postovarian testes. Didymorhynchus southwelli n. g., n. sp., described from Aetobatus narinari from Sri Lanka (Ceylon), is distinguished by a sharply delineated scolex, no neck, a bipartite cirrus, a bilobed ovary, lateral bands of vitelline follicles, a uterus with preformed diverticula and a preformed uterine pore. Zygorhynchus n. g. is distinguished by a sharply delineated scolex, a muscular cirrus sac with a single internal seminal vesicle, a muscular encasement of the distal vagina, vitelline follicles encircling the medulla and the absence of a preformed uterine pore. Zygorhynchus robertsoni n. sp. and Z. elongatus n. sp., from Himantura uarnak and H. toshi from Australia, differ in scolex measurements and armature. The Tetrarhynchobothriidae has affinities with both the homeoacanthous and heteroacanthous families of trypanorhynchs. Diagnostic characters include: two bothridia, acraspedote scolex, small hollow hooks, homeomorphous quincunxial metabasal armature, internal seminal vesicles or bipartite cirrus, vitelline follicles encircling the medulla or in lateral bands, uterus simple, linear, or with preformed diverticula.