Trischistoma taiguensis, Xu, Yu Mei, Zhao, Zeng Qi & Wang, Jian Ming, 2015

Xu, Yu Mei, Zhao, Zeng Qi & Wang, Jian Ming, 2015, A new species and a new record of Trischistoma Cobb, 1913 (Nematoda: Enoplida: Trischistomatidae) from Shanxi Province, China, Zootaxa 3937 (3), pp. 564-576 : 567-571

Description of Trischistoma taiguensis sp. nov.

(Figs 3A–E, 4A–J & 5A–C)

Measurements. Table 1 .

Material examined. Holotype: Female was deposited at the Nematology laboratory, Shanxi Agricultural University, Taigu, China, SXAU slide No. 451.

Paratypes: 8 females and 11 juveniles: SXAU slide Nos. 452–462.

Description. Female (n=9). Body dorsally bent when fixed, posterior region more curved than anterior (Fig. 3A). Cuticle with fine annulations, cuticular thickness about 1 µm at different body regions.

Head rounded, continuous with body contour, 8–10 µm wide. Outer labial setae and cephalic setae in two separate whorls (Figs 3B, 4A, 5A); six longer labial setae 5–6 µm long or 47–62% of head diameter, four shorter cephalic setae 2–3µm or 23–37% of head diameter, finer than the longer labial setae. Distance between labial setae and cephalic setae 5–6 µm. One conspicuous dorsal tooth, 10–11 µm from anterior end or 1.1–1.3 times head diameter; posterior dorsal tooth minute, 20–24 µm from anterior end or 2.0–2.9 times head diameter (Figs 3B, 4B). Amphid small, calyciform, 10–14 µm from anterior end (Figs 4C, 5A). Pharynx 133–149 µm long, occupying 21–24% of body length. Excretory pore not seen. Nerve ring 60–65 µm or 43–45% of pharyngeal length from anterior end of body (Figs 3B, 4D). Cardia between pharynx and intestine inconspicuous (Figs 3C, 4E).

Gonad prodelphic, 79–145 µm long, or 12–21% of body length, reflexed but tip not reaching vulva (Figs 3D & 4F).Vulva opening a simple slit, without sclerotized lips, occupying 15–17 % of body diameter; vagina short, 4–5 µm long, occupying 19–34% of body diameter (Figs 3D & 4G). Post-vulval uterine sac absent. Vulva to anus distance 65–87 µm long, or 1.3–1.8 times tail length. Tail length 42–55 µm, 7.1–9.1% of total body length, bent dorsally (Fig. 3E). Three tandem caudal glands, a small terminal spinneret and a pair of caudal setae on the tail (Figs 3E, 4H–4J, 5B–5C).

Male. Not found.

Diagnosis and relationships. Trischistoma taiguensis sp. nov. is characterized by its short body length and by having one pair of caudal setae on the tail.

The genus Trischistoma contains two groups of species, one with a post-vulval sac and one without ( Table 2). Trischistoma taiguensis sp. nov. belongs to the latter group, which includes T. turorehe , T. gracile , T. minor , T. waiotama , T. pellucidum and T. triregius .

Species L (mm) a b c c ′ V% Lip region Tail length References

Post-vulval uterine sac absent

tukorehe 1088 –1149 39–47 3.8–4.1 11–15 3.9–4.9 72– 76 12–16 75–92 Zhao 2011 Females of T. taiguensis sp. nov. differ from T. tukorehe and T. gracile by having a shorter body (562–699 vs 1088–1149 and 1060–1100 µm), more posterior vulva (V =79–82% vs 72–76% and 76–78%) and shorter tail (42–55 vs 75–92 and 82–86 µm). Morphologically, it is close to T. minor , but differs from it in having a greater distance between the outer labial setae and cephalic setae (5–6 vs 3–4 µm) and by having a pair of caudal setae on the tail (absent in the latter). It also tends to have a larger de Man’s b value (4.1–4.7 vs 3.7–4.2).

T. taiguensis sp. nov. differs from T. waiotama by having a shorter body (562–699 vs 675–908 µm), pharyngeal length (135–147 vs 171–198 µm), ventromedian cervical seta absent (one single seta present in the latter) and one pair of caudal setae on tail (absent in the latter); from T. pellucidum by having a shorter body (562–699 vs 680–850 µm), more posterior vulva (V =79–82% vs 73–74%), smaller lip diameter (8–10 vs 10–12 µm) and caudal setae (one pair vs absent); and from T. triregius in lacking lateral cervical setae (one pair present in the latter), having a smaller lip diameter (8–10 vs 10–12 µm) and caudal setae on the tail (one pair vs absent).

FIGURE. 3. Trischistoma taiguensis sp. nov. Female. A: Entire body. B: Anterior body region, lateral view, showing outer labial setae, cephalic setae, dorsal teeth and amphid. C: Oesophago-intestinal junction. D: Genital region. E: Tail. Scale bars: A=50 Μm, B, C, D, E=20 Μm.

FIGURE. 4. Trischistoma taiguensis sp. nov. photomicrographs, female. A: Pharyngeal region, lateral view, showing outer labial setae and cephalic setae in two whorls. B: Pharyngeal region, dorsal teeth arrowed. C: Pharyngeal region, lateral view, amphid aperture arrowed. D: Pharyngeal region, lateral view, nerve ring arrowed. E: Pharynx and intestine junction. F: Genital region. G: Vulval region, lateral view, vulva arrowed. H: Tail region, three tandem caudal glands arrowed. I: Tail region, caudal seta on the tail arrowed. J: Terminal spinneret.

FIGURE. 5. Scanning electron micrographs of Trischistoma taiguensis sp. nov. A: Head region, showing outer labial sensillae, cephalic seta and amphid aperture (arrowed). B: Tail, caudal seta on tail arrowed. C: Spinneret.

Based on the SSU and LSU molecular phylogenetic studies (Figs 1, 2), T. taiguensis sp. nov. from China differs from all the Trischistoma species with SSU and LSU sequences available in GenBank. When compared with molecular data for the most closely related species ( T. otaika from New Zealand), there are 1% (20 in 1624 bps including 1 gap) differences for SSU, and 8% (65 in 762 bps including 5 gaps) differences for LSU between the two species.

Habitat and locality. T. taiguensis sp. nov. was collected from a soil and litter mixture, 0–15 cm depth, under a pear tree ( Pyrus spp.), Taigu county, Shanxi Province (112°32′42.35˝ E, 37°25′14.85˝ N), in October 2012 by Jin Hua Wu.

Etymology. Species epithet is named for the type locality. Taigu is a county of Shanxi Province, China.

Tables

TABLE 1. Morphometric data for Trischistoma taiguensis sp. nov. (measurements in Μm ± S. D.)

character	holotype	paratype
n	1	8
L	699	598 ± 41 (562–688)
a	41.9	37.5 ± 2.4 (34.7–39.9)
b	4.7	4.3 ± 0.2 (4.1–4.7)
c	12.7	12.9 ± 1.0 (11.0–14.0)
c'	4.6	4.2 ± 0.3 (3.9–4.6)
V	81.5	80.2 ± 0.9 (78.9–81.4)
Head diameter	10.2	9.0 ± 0.5 (8.5–9.8)
Body diameter	16.7	16.0 ±1.6 (14.7–19.3)
Pharynx length	149	139.2 ± 4.1 (135–147)
Nerve ring-anterior end	65.1	61.3 ± 1.3 (60.2–63.1)
Tail length	55.0	46.4 ± 4.4 (42.1–53.5)
Anal body diameter	12.0	11.2 ± 0.5 (10.3–11.6)
Rectum length	13.4	10.0 ± 1.1 (9.3–12.1)
Vulva-anus distance	85.6	73.2 ± 7.9 (64.8–86.7)