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Tylocephalum Linton, 1890 (Cestoda: Lecanicephalidea) from the Cownose Ray, Rhinoptera bonasus (Mitchill, 1815) with a Discussion of Its Validity and Systematic Relationships1

1984; Helminthological Society of Washington; Volume: 51; Issue: 1 Linguagem: Inglês

0018-0130

Ronald A. Campbell, Allen D. Williams,

Crustacean biology and ecology

The first generic diagnosis of Tylocephalum, based upon Linton's type species, T. pingue, from the type host and locality is presented. Tylocephalum pingue is most common in cownose rays, Rhinoptera bonasus, from Chesapeake Bay but is occasionally found in summer migrants to southern New England waters. The description of T. marsupium Linton, 1916 is expanded based upon information contained in the original publication and careful examination of serial sections of Linton's type material. A new species, T. bonasum, from Rhinoptera bonasus, is described and critically compared with T. pingue. Histology and reconstruction of the internal anatomy of T. pingue and T. bonasum show that scolex variability can resemble either Hexacanalis Perrenoud, 1931 or Cephalobothrium Shipley and Hornell, 1906. Tylocephalum is diagnosed by its fungiform metoporhynchus and globose posterior portion of the scolex, herein termed the pars basalis, marginal genital pore, preovarian testes, conspicuous external seminal vesicle, unarmed cirrus, bilobed ovary and circumcortical vitellaria. Species having lateral bands of vitellaria but otherwise similar to Tylocephalum are referred to Cephalobothrium. Tetragonocephalum Shipley and Hornell, 1905, recognized by its external and internal seminal vesicles and lateral bands of vitellaria continuing into the postovarian space, is considered a lecanicephalid most closely related to Cephalobothrium.e systematic relationships of Tylocephalum to other lecanicephalans are discussed. Spinocephalum Deshmukh, 1980 is considered a junior synonym of Tylocephalum Linton, 1890. Hexacanalis Perrenoud, 1931 is considered a junior synonym of Cephalobothrium Shipley and Hornell, 1906. Historically, the taxonomy of certain of the lecanicephalans has been in a state of confusion because of the inadequacy of old descriptions and the lack of specimens for study. Linton's (1890) Tylocephalum, and Cephalobothrium of Shipley and Hornell (1906) are among the genera that have never been completely described and their true systematic status clarified. Tylocephalum pingue Linton, 1890, the type species of the ge- nus, was never described beyond scolex mor- phology nor were any type specimens deposited in museum collections. MacCallum (1921) de- posited specimens he believed to be T. pingue from hosts taken in the Atlantic and Pacific oceans but they are unsatisfactory for studying internal anatomy. Southwell (1925) emended Tyloceph- alum using the anatomy of Tetragonocephalum Shipley and Hornell, 1905, which he and Shipley and Hornell (1906) considered to be synony- mous with Tylocephalum. The continued lack of knowledge about T. pingue led to confusion in- volving the validity of Tetragonocephalum. Ya- maguti (1959) gave an expanded diagnosis of Tylocephalum, based upon descriptions of species he considered to be congeneric, and created a