Drilocephalobus moldavicus Lisetskaya, 1968

Boström, Sven & Holovachov, Oleksandr, 2018, Description of Drilocephalobus moldavicus Lisetskaya, 1968 (Rhabditida: Osstellidae) from Kelso Dunes, Mojave National Preserve, California, USA, Zootaxa 4514 (3), pp. 438-444 : 439-442

Drilocephalobus moldavicus Lisetskaya, 1968

( Figs 1–2 , Table 1)

Material examined. 5 females and one male on slides # SMNH-135940, SMNH-149148, SMNH-149149, SMNH- Type-8435 ( Nothacrobeles istvani ), SMNH-Type-8443 ( Nothacrobeles andrassyi ) deposited in the invertebrate collection of the Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden.

Locality and habitat: USA, California, Mojave National Preserve, Kelso Dunes , soil around roots of desert plants (N 34 53.698', W 115 42.155'; and N 34 53.365’, W 115 42.221’), 28 March 2010, legit O. Holovachov & P. De Ley.

* Number of annuli from anterior end to excretory pore and deirid, respectively

Description. Adult. Body generally arcuate ventrad when killed by heat, posterior end more strongly arcuate in male. Cuticle finely annulated, annuli about 1.3–1.7 µm wide at midbody. Lateral field with five incisures, occupying about 30% of body diameter, starting immediately at the posterior edge of the amphid and extending to phasmid and two incisures almost to tail terminus in both sexes. Lip region helmet-shaped, about 6.0–8.5 µm high and 5–7 µm wide, offset from body contour by the large, slit-like amphid openings; lips amalgamated, carrying 6 +4 papilla. Stoma almost absent, with thin walls lacking sclerotizations, stomatal aperture a small perforation. Pharynx without distinct divisions, cylindrical, widening slightly at about 1/3 of its length and basally, without valves; cardia short; base of pharynx enveloped by intestine. Nerve ring, excretory pore and deirid can only be seen in few specimens.

Female. Reproductive system monodelphic, prodelphic; ovary reflexed posteriorly at oviduct, ovary straight posterior to vulva. Vulva not protruding; vagina about one-third to two-fifths of vulval body diameter (VBD). Spermatheca well developed, rounded, about one body diameter (BD) long. Postvulval uterine sac (PUS) about 1.5 times VBD long. Tail straight or slightly curved ventrad, conoid-elongate with rounded terminus, about 20–24 ventral annuli. Rectum long, about 1.5 times anal body diameter (ABD). Phasmids located at about half of tail length.

Male. Similar to female in most respects, except for the sexual characters. Reproductive system monorchic, testis reflexed ventrad anteriorly. Spicules slender, paired and symmetrical, slightly curved ventrad; with oval manubrium and subcylindrical, gradually narrowing shaft. Gubernaculum plate-like. Genital papillae arranged as follows: precloacal and adcloacal papillae invisible if present; two pairs (one ventrosublateral and one lateral) at midtail; two pairs (one lateral and one dorso-sublateral) closer to tail terminus; any other papillae invisible if present. Phasmids located at about half of tail length. Tail slightly curved ventrad, conoid with rounded terminus.

Diagnosis (supplemented with literature data). Drilocephalobus moldavicus is characterized by a body length of 286–417 µm in females and 350–430 µm in males; cuticle finely annulated, annuli about 1.1–1.7 µm wide at midbody; lateral field with five incisures, extending to phasmid and two incisures almost to tail terminus in both sexes; lip region helmet-shaped, offset from body contour; lips amalgamated; stoma with thin walls lacking sclerotizations; pharynx without distinct divisions, cylindrical, widening slightly at about 1/3 of its length and basally, without valves; spermatheca 11–27 µm long; postvulval uterine sac 21–31 µm long; spicules 14–23 µm long; and female tail conoid-elongate with rounded terminus.

Remarks. The current specimens have the feature “lateral field with five incisures” in common with D. moldavicus Lisetskaya, 1968 , D. goodeyi Ali, Suryawanshi & Chisty, 1973 , and D. cameroonensis Siddiqi, 2001 . They differ from D. goodeyi by the shorter and differently shaped tail in both females (c = 9.8–12.3, conoid elongate with rounded terminus vs c = 7.8–9.3, conoid elongate with pointed terminus) and males (c = 15.2, conoid with rounded terminus vs c = 8.0–9.7, conoid elongate with pointed terminus); and longer spicules (23 µm vs 17– 19 µm). They differ from D. cameroonensis by the shorter and differently shaped tail in both females (28–36 µm, c = 9.8–12.3, c’ = 2.5–3.5, conoid elongate with rounded terminus vs 46–54 µm, c = 6.3–7.8, c’ = 4.0–5.4, conoid elongate with spicate terminus) and in males (26.5 µm, c = 15.2, c’ = 1.6, conoid with rounded terminus vs 43–47 µm, c = 7.4–7.6, c’ = 4.0–4.5, conoid elongate with spicate terminus); longer PUS (25–31 µm vs 10–12 µm); longer spicules (23 µm vs 13–15 µm) and gubernaculum (11 µm vs 6–8 µm). The current specimens are identified as D. moldavicus although they differ by having a somewhat more elongate female tail (28–36 µm, c’ = 2.5–3.5 vs 25–31 µm, c’ = 2.2–2.7); shorter male tail (26.5 µm, c’ = 1.6 vs 28–35 µm, c’ = 2.5–3.2); a more posterior position of phasmids in females (45–50% vs 31–42% of tail length); and slightly longer spicules (23 µm vs 14–21 µm).

Figures

FIGURE 1. Drilocephalobus moldavicus Lisetskaya, 1968. A. Anterior end, surface view. B. Female tail. C. Pharyngeal region. D. Female gonad. E. Male tail. Scale bar = 20 µm.

FIGURE 2. Drilocephalobus moldavicus Lisetskaya, 1968 females (A–I) and male (J–K), photomicrographs. A. Anterior end, surface view. B. Anterior end, median section. C. Labial region and amphid. D. Lateral field. E. Posterior part of pharyngeal region. F. Tail. G–H. Vulval region. I. Spermatheca. J–K. Cloacal region. Scale bars A–K = 10 µm.