A New Genus of Acanthocephala with Forked Lemnisci

Abstract

During the examination and study of the parasites of the Western robin,* (Turdus migratorius propinquus Ridgway), a number of acanthocephala were found. Their position in the family Polymorphidae is indicated by their parasitism as mature adults in the alimentary tract of birds and their long cement glands, while the total lack of body spines and insertion of the proboscis receptacle at the base of the proboscis would indicate they should be included in the subfamily Plagiorhynchinae Meyer 1931. Within the subfamily, however, the affinities of these worms are rather uncertain, since they do not fit completely into any one existent genus, but show characteristics of four, i.e. the genera Plagiorhynchus Liihe (1911), Porrorchis Fukui (1929), Prosthorhynchus Kostylew (Meyer, 1932), and Leuheia Travassos, 1919 (1926). Therefore, there has been erected for them a new genus Furcata, the type species being described in this paper. The name is derived from the lemnisci, which, strikingly different from those of any of the first four genera, are forked. Relationship with the genus Plagiorhynchus is established on the theoretical basis of forked lemnisci and on the mutual characteristic of spherical testes, but identity is excluded by (1) the genus Plagiorhynchus has six compact cement glands, the genus Furcata four elongate glands, (2) the eggs of the genus Plagiorhynchus have sharply constricted polar elongations of the middle membrane, the eggs of Furcata do not. Furthermore, although the possession of forked lemnisci is given as a possible generic characteristic of Plagiorhynchus, descriptions of the only species within the genus, the type species P. lanceolatus (Linstow) do not mention this feature. A comparison of the genus Furcata with the genus Porrorchis shows that the former differs from the latter in (1) relatively smaller size, (2) a more compact, elliptical body, (3) only one type of hook on the proboscis, (4) shorter cement glands, and (5) forked lemnisci. The two genera resemble one another in both having (1) short necks, (2) long lemnisci, (3) four cement glands, (4) no polar projections of the middle egg membranes, (5) lateral retinacula, and (6) the ganglion being placed in the posterior