Males: Length 1.5 mm (1.0 - 1.7); a = 50 (39 - 59); b = ?; c = 18 (14-25). n = 57
Female annulation 2.4 microns wide anteriorly, 1.6 um in the caudal region. Lip region not set off from body, bearing 9-11 annules and a terminal cap. Male lip region set off by a deep constriction, oval shaped, with 9-11 annules and a terminal cap. Female stylet with rounded basal knobs, 2.1 um by 6.4um; dorsal gland outlet approximately 3.5 um from base of stylet; median esophageal bulb 19 um (17-21um) wide by 20um (18-21um) long, that is, nearly spherical. Male stylet rudimentary, the forward part apparently a meandering tube which is generally indistinct, the posterior extension poorly developed with weak basal knobs. Median bulb and esophagus poorly developed, the median bulb showing only sclerotized valve structures. Female hemizonid two or more annules long, anterior to excretory pore; excretory pore less conspicuous than hemizonid, 235um (195-251um) from anterior end. Male hemizonid rarely seen, two or more annules long, immediately anterior to excretory pore; excretory pore 180 um (151-213) from anterior end. Ovaries didelphic, outstretched, anterior ovary 23%, posterior ovary 28% of total body length; spermatheca apparently weakly developed or absent. No opposing sclerotized pieces in the vagina. Testies outstretched. Spicules arcuate, 31.8um (28.0 -39.2um) long measured laterally on chord of arc. Gubernaculum 14.7um (11.2-16.0um) long with a short anterior flexture 2.9 um (1.4-4.2um) long. Female tail hemispherical with the terminis 8.4 um (7.0-9.8um) from the protoplasmic portion of the tail. Tail length 2.7 (1.6-3.8) time anal body width; phasmid 58um (48-67um) from tip of tail. Male tail (measured laterally along the chord) about 2.5 times longer than anal body width. Phasmid 44 um (35-53um) from tip of tail. Lateral alae in the adults appear as one line extending from the lip region to the terminus of tail in both sexes.
Immature Stages. B. euthychilus is separated from B. longicaudatus in the larval stages emerging from the eggs by the absence of a constriction in the neck region and the central lateral line extending from the tip of the head to the end of the tail, while the other two lateral lines begin 12 to 18 annules from the neck and extend to the end of the tail. In larval stages of B. longicaudatus there is a constriction in the neck region and the central lateral line is present in the head, absent in the first 8 to 10 annules from the head and begins again extending to the end of the tail; the other two lateral lines begin 40 to 50 annules from the neck constriction.
B. euthychilus is easily distinguished from B. gracilis by the qualitative characters but appears to be generally similar to it in measurements of total, anterior, posterior, stylet and tail lengths. However, analysis of variance of these characters indicate the differences are significant at the 95% level.
(Description- Rau, 1963)