Parasitology, Harold W. Manter Laboratory of
Date of this Version
1983
Abstract
The six species of Nematodirus parasitic in domestic ruminants of North America have been identified previously on the basis of characteristics of the bursa and tips of the spicules, and females could not be identified. In an effort to find additional diagnostic characteristics of both sexes, cuticular ridges were studied with light and scanning electron microscopy and in whole mounts and cross sections. After the cuticular ridges of males were characterized, females were matched with males by means of cuticular ridges, except for the rare species N. davtiani. Five of the six species have variations of an 18-ridge bilaterally symmetrical system in the cervical region. The sixth species has 26 cervical ridges. Two groups of species were recognized on the basis of cuticular characteristics correlated with other morphological characters. The two species in Group I, Nematodirus filicollis and N. dalviani, lose ridges laterally in the postcervical region and have 14 ridges at midbody. They can be identified by their anteriorly extended pattern of ridges in the cervical region. These two species also share the characteristics of finlike ridges, a small number (30-35) of perioral denticles, a short cephalic expansion, and a large bursa without a separate dorsal lobe. Nematodirus davtiani can be distinguished from N. filicollis by its prominent dorsalmost and ventralmost ridges and its distinctive dorsal ray. In contrast, the four species of Group II, N. helvetianus, N. oiratianus interruptus ssp. n., N. abnormalis, and N. spathiger, share the characteristics of a more posteriorly distributed pattern of ridges in the cervical region, 18 or more ridges near midbody, smaller dorsal and ventral ridges, a larger number (50-65) of perioral denticles, a longer cephalic expansion, and a smaller bursa with separate dorsal lobes. Nematodirus helvetianus and N. oiratianus interruptus add ridges in the cervical and postcervical regions, and are characterized by having more than 18 ridges for most of their length; they do not add ventral ridges in the last quarter of the males. Nematodirus helvetianus has more ridges (30-36 at midbody) than any of the other species. Nematodirus oiratianus interruptus can be easily separated from all other species by its discontinuous ridges in the cervical region. Nematodirus oiratianus oiratianus from Asia and South America have continuous ridges. Nematodirus spathiger and S. abnormalis have 18 ridges for most of their length; they lose all dorsal ridges and add a few ventral ridges in the last quarter of the males. Nematodirus abnormalis can be distinguished from N. spalhiger by the cervical discontinuities in ridges numbered 2 and 8, by spicular and bursal characteristics, and a more anterior vulva position. Possible evolutionary relationships among the six species are described in a cladogram and a key to species.
Comments
Published in Proceeings of the Helminthological Society of Washington 50(2).1983. pp. 261-274