Trischistoma helicoformis, Prado-Vera, Ignacio Cid Del, Ferris, Howard & Nadler, Steven A., 2016

Prado-Vera, Ignacio Cid Del, Ferris, Howard & Nadler, Steven A., 2016, Five new species of the family Trischistomatidae (Nematoda: Enoplida) from North and Central America, with keys to the species of Trischistoma and Tripylina, Zootaxa 4109 (2), pp. 173-197 : 181-183

Trischistoma helicoformis n. sp.

Measurements. Table 1 .

Trischistoma helicoformis n. sp. was collected by the second author from lichen on a shrub along the Carretera Interamericana in Costa Rica in August, 2012.

Female (n=18). Body slender without somatic setae, spiral shaped when relaxed, bent dorsally at the posterior end with tail dorsally reflexed after fixation. Cuticle thin, (1.0 µm) and finely striated under SEM; lip region continuous, rounded and asymmetric, 10–15 (12±0.35) µm wide and 13–16 (13±0.4) µm at the level of the cephalic setae which are 10–15 (12±0.37) µm from the anterior end. The vulva is at 67–79 (70±0.4)%; the index b = 3.9–4.6 (5.7±0.16) (Figs. 5,6).

Mouth with three lips, opening somewhat dorsally shifted, mouth cavity narrow, encircled by pharyngeal musculature. Cephalic sensillae in three whorls: the inner labial setae are very small and thin, raised slightly above the cuticular surface at the base of each lip; the six outer labial setae are oriented slightly anteriorly and 4–6 (5±0.25) µm long, almost 50% of labial diameter; the four cephalic setae are 3–4 (3.0±0.1) µm long, much thinner than outer labial setae and 11–14 (11±0.3) µm from the anterior end. Amphid apertures posterior to cephalic setae, 15–27 (21± 1.0) µm from the anterior end. One cervical seta at 24 µm from the anterior end. Dorsal tooth small 13–19 (15.8±0.42) µm from the anterior end and subventral teeth 10–14 (12.4±0.4) µm anterior to the dorsal tooth. Pharynx cylindrical, strongly muscular in its posterior part, 170–264 (235±5.65) µm long and 15–27 (23 ±0.58)% of the total body length, terminating in a small cardia, 3–8 (5.2±0.58) µm long and 4–11 (8.1±0.48) µm wide (Figs. 5,6).

Genital system monovarial prodelphic without a post-uterine sac. Ovary extending anteriorly, not reflexed, vulva to anus distance 94–179 (131±5.09) µm. Distance between pharynx base and vulva 452–594 (564±26.3) µm. Vulval lips do not protrude and have thin sclerotised structures. Tail elongate conoid, regularly tapering, dorsally bent, 76–101 (87±1.9) µm long, 16–22 (20±0.5) µm wide at anus level, and 6.9–10.0 (8.6±0.17)% of total body length. A pair of setae in latero-dorsal position on the tail posterior to the anus. Rectum 10–25 (16±0.97) µm long. Spinneret small, 2.0 µm long ( Fig. 5 ).

Male: Unknown.

Type habitat and locality. Lichen growing on bark of shrub 20 m from the east side of the Carretera Interamericana, Costa Rica, N 9°34'22.6" W 83°45'26.8", 3341 m above sea level.

Type specimens. Holotype female CNHE 9260 and paratypes CNHE 9261 of T. helicoformis are deposited in CNHE; paratypes in CNCP (A-081-2), UCRNC and USDANC.

Etymology. The specific epithet come from the Greek ”helix” and refers to the spiral shape of the body when disturbed and after death.

Diagnosis and relationships. The new species is characterized by the spiral shape of the very thin body after death, the length of the tail 76–101 (87±1.9) µm, the indices c= 10–15 (12±0.25) and c’= 4.0–6.3 (3.7±0.1); thin cuticle, the position of the vulva 67–85 (78±0.8)%, and the length of the pharynx, 170–264 (235±5.6) µm long ( Fig. 5 , Table 1 ).

Trischistoma helicoformis n. sp. is close to T. ripariana n. sp., and T. corticulensis n. sp. in the size of the body, outer labial setae, the thin cuticle and index b. It can be readily distinguished from them by the spiral habit of the dead body. From T. ripariana n. sp., it differs in the length of the tail 76–101 (87±2.0) vs. 34–57 (46±1.8) µm, the size of the pharynx 170–264 (235±5.6) vs. 188–236 (213±2.6) µm, in the absence of a post-uterine sac and in the range of the position of the vulva 67–85 (78±0.8) vs. 79–83 (81±0.2)%. It differs from T. corticulensis n. sp. in the length of the tail 76–101 (87±2.0) vs. 51–84 (65±2.9) µm, in the length of the pharynx 170–264 (235±5.6) vs151–217 (181±6.2) µm and by the index c = 10–15 (12±0.3) vs. 14–19.5 (16±0.6), in the length of the tail, 76–101 (87±2.0) vs. 51–84 (65±2.9) µm and the vulva to anus distance, 94–179 (131±5.0) vs. 194–286 (247±8.9). It resembles T. otaika Zhao, 2011 , in the length of the body, and in the indices a and b, but it can be distinguished by the absence of a post-uterine sac, length of the tail, 51–84 (65±2.9) vs. 81–98 (91±7.0) µm and the length of the body 0.88–1.2 (1.0±0.2) vs. 1.2–1.3 µm ( Table 1 ).

Molecular characteristics. Trischistoma helicoformis was identical in sequence to T. veracruzense , but differed from other Trischistoma congeners by 13 or more nucleotide differences in pairwise congeneric comparisons. There are strong morphological differences that distinguish the two species: T. veracruzense has a post-uterine sac but T. helicoformis does not and the body form of T. helicoformis , when disturbed by touch or when relaxed by heat, is a tight spiral while that of T. veracruzense is an open C-shape with the posterior part curved dorsally.

Figures

FIGURE 5. Trischistoma helicoformis n. sp. Female A – E. A: Anterior end; B: Vulva region; C: Pharyngeo-intestinal junction; D: Caudal setae lateral view; E: Body shape after death.