Notes on Tetraphyllidean Cestodes from the Atlantic Coast of North America, with Descriptions of Two New Species

Abstract

The genus Rhinebothrium Linton, 1890 (Tetraphyllidea: Phyllobothriidae) is redefined and considered valid. Rhinebothrium spinicephalum sp. n. and R. lintoni sp. n. are described from the southern stingray, Dasyatis americana Hildebrand and Schroeder. The phyllobothriid, R. maccallumi Linton, 1924, and the oncobothriid, Acanthobothrium tortum (Linton, 1916), are redescribed. Discovery of a hermaphroditic specimen of Dioecotaenia cancellata (Linton, 1890) indicates that the dioecious character of these cestodes is not absolute. Until recently, little has been done to clarify or contribute to the knowledge of the elasmobranch cestode fauna from the western North Atlantic since the work of Linton. Linton's descriptions of helminths of teleost and elasmobranch fishes frequently are too inadequate for accurate identification. Furthermore few of Linton's type specimens are available and, of those that are, many have faded and partially disintegrated. Linton (1890) described the genus Rhinebothrium to accommodate species resembling Echeneibothrium, a genus common to the eastern North Atlantic and Mediterranean Sea, but lacking a myzorhynchus (rostellum). He included four species in this genus. Among Linton's descriptions only two dealt with species of Echeneibothrium. One (E. austrinum Linton, 1924) is considered inadequately described, and the second (E. vernetae; syn. E. variabile Beneden sensu Linton, 1889) was redescribed as a new species by Euzet (1956a). The validity of the genus Rhinebothrium has been questioned by Wardle and McLeod, 1952; Young, 1956; Yamaguti, 1959; and Alexander, 1963; and is considered as synonymous with Echeneibothrium. However, Baer (1961) and Williams (1966) have provided evidence that Rhinebothrium may be distinct from Echeneibothrium. Recent collections of elasmobranch cestodes from the Atlantic Coast and Chesapeake Bay have disclosed two new species of Rhinebothrium and sufficient material to better define the morphology of R. maccallumi Linton, 1924. Cestodes designated as Rhinebothrium cancelReceived for publication 18 September 1969. latum by Linton (1890) were recovered from two cow-nosed rays, Rhinoptera bonasus (Mitchill). Schmidt (1969) examined specimens of this cestode from a single cow-nosed ray and found their morphology unlike that of any other family in the order Tetraphyllidea. Due to the unusual characters of these cestodes, among which Schmidt cites their separate sexes, he designated Dioecotaenia cancellata (Linton, 1890) gen. et comb. n. and proposed the new family Dioecotaeniidae. My recovery of a hermaphroditic specimen of Dioecotaenia indicates that the dioecious character of these cestodes is not absolute. This paper also describes in detail Acanthobothrium tortum (Linton, 1916), an oncobothriid recognized as a member of Acanthobothrium by Southwell (1925) and briefly redescribed by Baer and Euzet (1962). MATERIALS AND METHODS Elasmobranchs were collected during the summers of 1967 and 1968 in Atlantic coastal waters from New Jersey to Chesapeake Bay, Virginia. Through the cooperation of the Virginia Institute of Marine Science, hosts were collected in trawling nets, or with hook and line. Specimens of Acanthobothrium tortum, donated by Dr. R. J. Goldstein, Emory University, were collected at the Cape Haze Marine Laboratory, Sarasota, Florida. Helminths were fixed in situ or removed from the spiral valve, studied alive, and fixed without pressure in alcohol-formol-acetic acid (AFA) at room temperature. Whole mounts were stained with Ehrlich's acid hematoxylin or Mayer's paracarmine, cleared in methyl salicylate, and mounted in Permount. Frontal and transverse serial sections were stained in Heidenhain's iron hematoxylin and eosin. Drawings were made with the aid of a camera lucida and microprojector. All species were compared with available specimens from the USNM Helminthological Collection. Measurements