Studies on four atypical species of the genus Labronema Thorne, 1939 (Dorylaimida, Qudsianematidae)

Abstract

Type material of

Labronema hyalinum and L. pacificum, as well as a recent population of L. neopacificum from Vietnam, all of them having in common a nearly continuous lip region, are examined, (re-)described and illustrated. Labronema hyalinum is characterized by its body 2.86-3.93 mm long, lip region truncate and 32-34 μm wide, odontostyle 44-48 μm long with aperture occupying 38-40% of its length, neck 747-856 μm long, pharyngeal expansion 378-422 μm long or 48-51% of total neck length and surrounded by a delicate (non-muscular) sheath, uterus tetrapartite and 469-608 μm long or 3.7-4.3 times the corresponding body diameter, pars refringens vaginae with two separate pieces, vulva longitudinal (V = 49-52), tail short and rounded (34-36 μm, c = 93-101, c’ = 0.5-0.6), spicules 120 μm long, and 31 contiguous ventromedian supplements. Labronema pacificum is characterized by its body 2.30-2.78 mm long, lip region continuous and 22 μm wide, odontostyle 32 μm long with aperture occupying about one-half its length, neck 517-600 μm long, pharyngeal expansion 305 μm long or 51% of total neck length, V = 47, tail short and rounded (23- 36 μm, c = 78-100, c’ = 0.4-0.6), spicules 82 μm long, and 16-22 nearly contiguous ventromedian supplements. New data, including SEM observations, are provided for L. neopacificum. The material originally studied by Thorne (1939) as belonging to L. pacificum is re-described as L. distinctum sp. n., being characterized by its body 1.04-1.13 mm long, lip region continuous and about 10.5 μm wide, odontostyle 14.0-15.5 μm long with aperture occupying 47-49% of its length, neck 273-292 μm long, pharyngeal expansion 123-134 μm long or 45-46% of total neck length, uterus short, pars refringens vaginae with two separate pieces, vulva longitudinal (V = 52), tail rounded conoid (13-17 μm, c = 63-79, c’ = 0.6-0.8), spicules strongly curved ventrad and 40-48 μm long, and 11-12 shortly spaced ventromedian supplements. A short discussion on the morphological variation observed within the genus Labronema is also presented.