Bursal Bosses as a Diagnostic Character in Nematodirus of Domestic Sheep, Ovis aries, in the United States

Abstract

Bursal bosses of six species of Nematodirus were studied. Three basic groupings were found. The bosses were generally distributed between the postero-lateral and ventro-ventral rays in N. spathiger and N. helvetianus. The lateral bursal lobes of N. davtiani were covered with bosses from the dorsal ray to anterior to the ventro-ventral ray. Bosses were distributed from anterior to the ventro-ventral ray to the postero-lateral ray in N. filicollis, N. abnormalis, and N. oiratianus. N. helvetianus had significantly more bosses per lateral bursal lobe than N. spathiger. N. abnormalis had significantly more bosses than N. oiratianus but N. oiratianus had a significantly larger boss. No significant differences (0.05 level) were found in the relative size of the largest boss and number of bosses between the left and right lobes of the bursae of each of four species of Nematodirus. The role of bursal bosses as a diagnostic character for trichostrongylids has been mentioned in the literature; however, a detailed analysis for their use as a taxonomic character apparently has not been made. Veglia (1915) illustrated the bosses on the bursa of Haemonchus contortus as well as the ridge of the internal groove. May (1920) used the bosses as a taxonomic character to aid in distinguishing some species of Nematodirus but gave no indication that a detailed analysis was made. Sarwar (1956) used cuticular markings on the lateral lobes of the bursae of some trichostrongylids as a taxonomic character in separating certain genera; however, his illustrations are inadequate. Illustrations of the bosses on the lateral lobes of the bursae of Nematodirus from domestic sheep in the United States suggest that the bosses might be used as a taxonomic character (Becklund and Walker, 1967). This paper presents a detailed analysis of their taxonomic value in six species of Nematodirus. MATERIALS AND METHODS Males of six species of Nematodirus were selected, with the aid of a dissecting microscope, from 27 lots of specimens collected from domestic sheep, Ovis aries, in the United States. The males had been stored in a preservative consisting of 92 parts of 70% ethyl alcohol, three parts formalin, and five parts glycerine. They were studied with the aid of the compound microscope in water and cleared in lactophenol. The bosses were more discernible following rehydration; whereas, clearing enabled better observation of the ridge of the internal groove. The bosses were studied and illustrated from both the medial and lateral aspects Received for publication 10 May 1968. 891 of the outstretched lateral lobes which were manipulated to expose their maximum surface. Ten to 20 males of N. abnormalis, N. filicollis, N. oiratianus, (= N. lanceolatus) (Samson, 1968), N. helvetianus, and N. spathiger were studied. N. davtiani is uncommon in domestic sheep and the numbers available were limited. All measurements are expressed in microns and were determined with the aid of a calibrated ocular micrometer. To determine if there were any differences between the bosses on the right and left lateral lobes of individual males of N. abnormalis, N. filicollis, N. oiratianus, and N. spathiger, the numbers of bosses present on each lobe and the size of the largest boss were determined (Table I). The size and number of the bosses of N. helvetianus and N. spathiger were compared. Similar comparisons were made between N. oiratianus and N. abnormalis (Table II). The difference between the two arithmetic means was compared with Student's t test at the 0.05 level of significance. Twenty-three possible specific distinguishing characters relating to the bosses were considered during the study, but only five of these were sufficiently consistent to warrant mentioning in the results. These were: (1) The relative distribution and patterns of the bosses on the inner and outer surfaces of the lateral bursal lobes. (2) The number of bosses as counted from the outer surface of the bursal lobes. (3) The distribution of the ridge of the internal groove of the bursae. (4) The general gross appearance of the bosses on the lateral surface of the bursal lobes. (5) The size of the largest boss between the latero-ventral and the externo-lateral rays.