Specific Characters in the Genus Trichuris, with a Description of a New Species, Trichuris tenuis, from a Camel

Abstract

In a recent paper. on the specific identity of whipworms from swine. Schwartz (1926) points out that the specific characters in the genus Trichuris Roederer 1761 are largely limited to the size of the spicules, the structure of the sheath, and the size of the eggs. Less important and more variable specific characters include the total size of the worms and the ratio of the slender anterior portion of the body to the relatively thick posterior portion. Baylis (1929) relies on the same characters for differentiation of species. The unsatisfactory nature of these characters, unsupported by other features, is obvious from the fact that whipworms as common as those in man and pigs were almost universally regarded as specifically distinct until 1926, when Schwartz showed that when a sufficient number of specimens were examined, no morphological differences could be demonstrated between the worms obtained from pig, man, or lower primates. Examination of a few specimens would not, however, have made this evident, for the range of variation in the few characters which had to be depended upon is such that apparently valid morphological differences could have been observed, as was actually done by a number of helminthologists in the past. A brief review of these characters shows how unreliable they are, especially when a limited amount of material is available for examination. Of the characters mentioned the size of the spicules is undoubtedly the most dependable one, and in conjunction with other characters is valuable in differentiation of species. The length in different species varies from about 9 to 11 mm. (8.6 to 10.4 according to my measurements) in T. vldpis of dogs and foxes, to about 0.75 mm. in T. muris of rats and mice. There is, however, considerable individual variation in the length of the spicules within a single species, and in many species, even in related hosts, there is considerable overlapping, so that this character alone is not always dependable. Thus in T. trichiura the measurements vary from 2 to 3.4 mm., while in T. ovis they are usually given as from 5 to 6 mm., but two measurements made by the writer were 7 and 7.65 mm. The spicule is always filamentous in form, and varies in diameter in different species, tapering more in some than in others; but the shape of the tip is not always a dependable character, as Schwartz showed in the case of T. trichiura.