Ditylenchus parvus Zell, 1988

Hashemi, Kobra & Karegar, Akbar, 2019, Description of Ditylenchus paraparvus n. sp. from Iran with an updated list of Ditylenchus Filipjev, 1936 (Nematoda: Anguinidae), Zootaxa 4651 (1), pp. 85-113 : 95

8. Ditylenchus parvus Zell, 1988

19 females: L = 690 (541–813) µm; stylet = 7.2 (6.5–8) µm; pharynx = 121 (110–141) µm; tail = 70.6 (53–102); a = 41.5 (35.3–49.6); b = 5.7 (4.8–6.9); c = 9.9 (6.9–11.0); c′ = 6.3 (4.8–7.9); V = 73.5 (70.8–75.2); V′ = 81.9 (80.4– 83.0); PUS/VBW = 2.7 (1.0–3.6); PUS/V-A = 35.6 (17.8–45.8) %; V-A/T = 1.6 (1.1–1.9).

7 males: L = 595 (442–717) µm; stylet = 7.0 (6.5–7.5) µm; pharynx = 111 (95–128) µm; tail = 63.9 (44–87.5) µm; a = 44.7 (34.7–57.8); b = 5.3 (4.4–6.0); c = 9.5 (8.2–10.3); c′ = 6.2 (4.6–8.2); spicules = 14.6 (12–17).

Diagnosis. D. parvus is characterised by four lateral field incisures, delicate, short stylet with rounded knobs, pyriform basal pharyngeal bulb that is offset or slightly overlapping (up to 4 µm), position of vulva, variable length of post-vulval uterine sac, usually pointed and sometimes mucronate tail tip, and short spicules.

The Iranian populations of D. parvus in this study in comparison to those of Brzeski (1998) have a slightly overlapping basal pharyngeal bulb (vs. offset) and stylet knobs sometimes sloping backwards (vs. rounded). D. parvus is similar to D. emus , D. equalis , D. exilis and D. terricolus . It can be distinguished from D. emus by the lower V value (70.8–75.2 vs. 79–81) and pointed tail tip (vs. rounded), from D. equalis by lower V (70.8–75.2 vs. 77–84) and shorter range of spicule length (12–17 vs. 14–25 μm), and from D. exilis by lower V (70.8–75.2 vs. 77–81) and greater PUS/VBW ratio (1.0–3.6 vs. 0.6–1.0).

D. parvus bears the most resemblance to D. terricolus . The differences between these two species are the structure of median and basal pharyngeal bulbs and the shape of the tail tip ( Brzeski 1991). The median bulb is more elongated in the second species, although intermediate forms were seen in individuals of some populations in this study. Also, the basal pharyngeal bulb slightly overlaps the intestine in the second species, which was observed in this study’s populations and another Iranian population (Karegar et al. 1995). On the other hand, according to Brzeski (1991), the tail tip in the first species is pointed, and in the second species is variable, with a thick terminus, while in the populations of this study, a wide variety of tail shapes, from rounded to pointed or mucronate, was observed. Since the populations of this study were generally more similar to D. parvus , they are retained under this name until further investigations can be made. It should be noted that two individuals from one population, in the present study have characteristics outside the range of other populations, which include a longer tail (91–102 vs. 53–80 μm), as well as lower PUS/VBW and PUS/V-A ratios (1.0–1.3 and 17.8–23.4 % v s. 1.7–3.6 and 28.7–45.8 %, respectively). In terms of characteristics, these two individuals were more similar to D. equalis , but due to the value of V (70.8–71.6) being similar to D. parvus and the greater stability of this character, they were placed in D. parvus .