Variation in taxonomic characters of a species of Acrobeloides (Cobb, 1924) Steiner and Buhrer, 1933

Abstract

Shape of the labial probolae and tail, configuration of the reproduction system, and position of the nerve ring, excretory pore, deirid, and phasmid were variable in a species of Acrobeloides (Cobb, 1924) Steiner and Buhrer, 1933, reared in bacterial cultures and subsequently in oven-dried soil. In soil, probolae were apiculate in 85% of the nematodes from six colonies (progeny of three females from red pine roots and three females From greenhouse soil), and 74% had conoid tails. In the six bacteria-reared colonies, 44% of the nematodes had conoid probolae, 32% were knobbed, 21% low-rounded, and only 3% were apiculate. Most of these specimens had hemispherical tails (57%), 18% were clavate, and 24% conoid, of which 16% had rounded tail termini and 8% were truncated. In the 12 colonies, always one shape predominated with at least 70% of the probolae and 47% of the tails of one shape. Intermediates were present in most colonies. There was a significant difference in body length between the colonies originating from red pine and those from greenhouse soil when reared on bacteria, but not when reared in soil. Position of the nerve ring, excretory pore, and deirid varied in relation to one another, to the esophagus, and in distances from the head, and generally were more anterior on the body in soil than in bacterial populations. The nerve ring extended from the metacorpus in 12% of the total specimens to as low as the base of the isthmus in less than 1% of all colonies. The nerve ring surrounded the anterior portion of the isthmus in fixed specimens in at least 75% of the females, but usually surrounded the metacorpus in living specimens. The excretory pore was generally located immediately below the nerve ring, but sometimes was opposite or as much as 12 μ below the nerve ring. The deirid was always observed below the excretory pore, usually at the base of the esophagus. The phasmids tended to be more posterior on hemispherical- or clavate-shaped tails than on conoid-shaped tails. Ovaries lacked flexures in young adults, the oogonia were arranged in contraposition or in tandem, and the vulval lips were seldom protuberant. Egg-laying females had ovaries with double flexures, oogonia in contraposition, and the vulval lips often were protuberant. Measurements of body dimensions and illustrations are provided. The species is compared with Cephalobus nanus de Man, 1880, for which Acrobeloides nanus is proposed as a new combination.