Oncholaimus minor, Chen & Guo, 2014

Chen, Yuzhen & Guo, Yuqing, 2014, Three new species of free-living marine nematodes from East China Sea, Zootaxa 3841 (1), pp. 117-126 : 121-123

Oncholaimus minor sp. n.

( Figure 2 , Table 3 )

Type material. Five males and one female from station XMHC L1 were collected in October 2011. Holotype, ♂ 1 on slide number XMHC20111015 L108.

Paratypes: ♂ 2 on slide number XMHC 20111015 L119, ♂ 3 on slide number XMHC 20111015 L125, ♂ 4 on slide number XMHC 20111015 L123, ♂ 5 on slide number XMHC 20111015 L118, ♀ 1 on slide number XMHC 20111015 L110.

Type locality and habitat. Intertidal sandy sediment at Huangcuo coast, Xiamen. Characteristics of surface sediment: see Table 1 .

Etymology. This species is named for its smaller body size.

Description. Body length 1541–2002 µm; maximum diameter 27–49 µm. Cuticle smooth. Head diameter 20–26 µm, continuous with body contour. Six lips with six small labial papillae. Ten cephalic setae in one ring, six 7–8 µm and four 5–6 µm. Deep barrel-shaped buccal cavity with strong cuticular walls, one larger left subventral tooth and two smaller right subventral and dorsal teeth. Amphids cup-shaped with shallow fovea, 0.27–0.43 cbd and situated at 14–18 µm from anterior end. Pharynx long, cylindrical and muscular, 0.19–0.21 times body length, surrounded by nerve ring about mid-way along its length. Excretory pore opening ventrally 52–68 µm from anterior end. Nerve ring 145–199 µm from anterior end. Pharynx length 310–390 µm. Tail shape displays sexual dimorphism.

Male: tail conico-cylindrical, stout and short, bearing two lateral setae and three terminal setae, obviously bent in middle. Cloacal opening surrounded by 12 sturdy genital setae arranged in single whorl. Spicules short and straight, 24–25 µm (0.9–1.4 abd), with distal half swollen and pointed tip. No gubernaculum. Several papillae present along the cloacal edge. Spinneret small, terminal.

Female: Tail much longer than that of male (93 µm vs. 45–56 µm), slightly ventrally curved. Vulva at 70.2% of body length. Demanian system situated on the right side of the intestine. Spinneret as in male.

Diagnosis and discussion. Oncholaimus minor sp. n. is characterized by its relatively smaller body size and sexual dimorphism in tail shape (the male tail is short and stout, c’ = 2.0–2.9, bent in middle, while the female tail is only slightly curved, c’ = 3.5). The new species most closely resembles O. manilius Gerlach, 1957 , O. martini Wieser, 1959 and O. brachycercus de Man, 1889 in the similar shape of male tail, whereas the female tail shape of the new species is rather different from these three species. Besides, O. minor sp. n. can further distinguished from these three species by the smaller body length, lower b ratio, shorter spicule length and more slender male tail; it also has fewer circumanal genital setae.

Figures

FIGURE 2. Oncholaimus minor sp. n. A: lateral view of male head end; B: lateral view of female head end; C: lateral view of male tail; D: lateral view of female tail; E: lateral view of male anterior part. Scale bar: A, B, C, D = 20µm; E = 50µm.