A Reconsideration of the Acanthocephalan Family Rhadinorhynchidae

The family name RHADINORHYNCHIDAE (PALAEACANTHOCEPHALA) dates from 1923 when Travassos elevated to family rank the sub-family RHADINORHYNCHINAE proposed by Luhe in 1912 to include the genus Rhadinlorhynchus and the concept of the genus Serrasentis, then known as Echinogaster. In elevating the rank of the group, Travassos added the genus Polyacanthorhynlchus to the new family concept. Travassos (1926) in his diagn-sis of the RHADINORHYNCHIDAE emphasized the extreme elongation of the proboscis and the presence of eight elongated cement glands as distinctive for the family. Chandler (1934) called attention to the fact that Luhe (1911) and other workers had not mentioned the number of cement glands in R. pristis and in some other species of Rhadinorhynchus, but stated is probable that if the type species R. pristis had less than the usual eight, the fact would have been mentioned by Liihe. During the past quarter century numerous studies have extended the original concept of the genus Rhadinorhynchus as well as the concept of the family, and have added several distinct genera to the family group. Meyer (1932) in his monograph on the ACANTHOCEPHALA assembled nine genera under this family caption. To these, still other more recently recognized genera must be added, until at present thirteen genera are attributed to this family (See Table 1). Among the diverse species now included in the expanded concept of the family the form of the proboscis and number of cement glands, which Travassos considered as diagnostic, now fail as unifying characters on which to base the family. Several of the forms have superficial resemblances to the genotype, but differ in essential morphological details. Chandler (1934) recognized two new genera (Gorgorhynchus and Nipporhynchus) chiefly on the basis that each has four cement glands in the male instead of the eight characteristic for Rhadinorhynchus. In order to evaluate the various discrepancies which have been insinuated into the family concept, it has seemed timely to offer a critical reconsideration and rearrangement of the genera and species ascribed to the RHADINORHYNCHIDAE.