Nematodirus of Domestic Sheep, Ovis aries, in the United States with a Key to the Species

Abstract

One hundred and thirty lots of specimens deposited in the U. S. National Museum Helminthological Collection and labeled as containing Nematodirus from domestic sheep, Ovis aries, in the United States were examined. Specific determinations were made on the 90 of these lots which contained males. They were collected in 21 states and the District of Columbia. Nematodirus spathiger was found in 80% of the 90 lots, N. abnormalis in 53%, N. filicollis in 22%, N. lanceolatus in 9%, N. helvetianus in 4%, and N. davtiani in 2%. Nematodirus spathiger is the most common species and was found among specimens collected in 19 states. Nematodirus abnormalis, previously reported from only eight states, was found from 18 states. Contrary to general belief, it appears to be, on the basis of this material, considerably more prevalent than N. filicollis, which was found in small numbers in lots collected in 10 states. Nematodirus helvetianus and N. lanceolatus were both found among specimens collected in four states and N. davtiani in one state. The distribution of the six species is given by state along with a discussion of each species, and a key with illustrations as an aid in their identification. Accurate information on the geographic distribution of parasites of domestic animals in the United States is still incomplete. The sources of such information and the problems involved in its compilation have been discussed in a checklist (Becklund, 1964). Several sources were consulted in compiling this checklist, including the records of the U. S. National Museum Helminthological Collection. At that time, some of the determinations in the Collection records of the genus Nematodirus were checked with their corresponding specimens on deposit and inaccuracies were found, e.g., specimens determined as being N. filicollis (Rudolphi, 1802) Ransom, 1907, were actually N. spathiger (Railliet, 1896) Railliet and Henry, 1909, or were a composite of several species. Subsequently, incorrect determinations were again noted when specimens of Nematodirus from domestic sheep were being examined for possible representatives of a new species. These observations suggested that a complete study of the specimens deposited as Nematodirus from domestic sheep in the United States would be of considerable value to correct the Collection records, ascertain the species present, and contribute accurate information on their distribution. The information reported herein is a result of that study. MATERIALS AND METHODS This study encompassed the examination of almost every lot of Nematodirus collected from Received for publication 6 February 1967. domestic sheep in the United States that has been deposited in the U. S. National Museum Helminthological Collection since its inception in 1893. The lots on deposit contain from one to several thousand specimens. The condition of the specimens varies from excellent to partially decomposed and fragmented. Relatively few Nematodirus from domestic sheep were deposited after 1950. Males only were selected for use in making specific determinations. The chief characters used in making these determinations were the morphologic structure of the spicule tip, the size of the lobules on the dorsal lobe of the bursa, and the relationship of the externodorsal ray to the dorsal margin of the lateral bursal lobes. The males were removed from the preserving fluid (92% of 70% alcohol, 3% formalin, and 5% glycerin) and cleared in lacto-phenol or pheno-alcohol for study. When male specimens were present in large numbers they were initially cleared, studied under the dissecting microscope (up to 54 X magnification), and a representative sample selected for close study and specific determination. The number of specimens in the sample varied, depending primarily on total number of males and on apparent number of kinds as revealed by the initial examination; in many instances more than a hundred males were examined. In the lots containing a smaller number of males, usually all specimens in the bottle were subjected to careful study.