Oncholaimus xiamenense, 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 : 123

Oncholaimus xiamenense sp. n.

( Figure 3 , Table 4)

Type material. Five males and two females from station XMGLY H1 and XMHC L2 , M2 , H1 , H2 , were collected in January and June 2011. Holotype, ♂ 1 on slide number XMGLY20110107 H101.

Paratypes: ♂ 2 on slide number XMHC20110622 H114, ♂ 3 on slide number XMHC20110622 H113, ♂ 4 and ♀ 1 on slide number XMHC20110622 H210, ♂ 5 on slide number XMHC20110622 L202, ♀ 2 on slide number XMHC20110622 M206.

Type locality and habitat. Intertidal sandy sediments at Gulangyu and Huangcuo coasts, Xiamen, East China Sea.

Characteristics of surface sediments in Table 1 .

Etymology. This species is named for the type locality, intertidal sediments at Xiamen.

Description. Body length 2480–3012 µm; maximum diameter 34–50 µm. Cuticle smooth. Head diameter 23–27 µm, continuous with body contour. Six rounded lips with six small and indistinct labial papillae. Ten cephalic setae in a circle are almost equal length. Large barrel-shaped buccal cavity, 27–32 µm deep and 12–15 µm wide, its walls heavily cuticularized and armed with three teeth: left subventral tooth larger than right subventral and dorsal teeth. Amphids cup-shaped with shallow fovea, about 0.4 cbd and situated at 18–21 µm from anterior end. Pharynx cylindrical and muscular, 0.14–0.16 times body length, surrounded by nerve ring about midway along its length. Excretory pore 88–112 µm from anterior end. Nerve ring 197–220 µm from anterior end. Pharynx length 399–432 µm. Tail shape displays pronounced sexual dimorphism.

Male: tail conoid, ventrally arcuate. A distinct ventral tubercle approximately 3/4 of distance from cloaca to tip of curved tail. One row of ventrosublateral sturdy genital setae present on either side of cloacal opening, three posterior to cloaca and three anterior in each row. In addition there are four subdorsal setae. Two outstretched opposed testes about equally long, anterior testis on the right side of the intestine, posterior one also mainly on the right side. Spicules slightly ventrally curved, 44–52 µm long as arc (1.4–2.0 abd), with pointed tip and slightly cephalated proximal end. Gubernaculum absent. Spinneret obvious, appearing as a cap covering the tip of tail.

Female: tail broadly convex for about one anal body width, then abruptly narrowing to a long peg of about the same length as the broad basal part. Ovary single, with only the anterior reproductive branch developed, lying on the right side of the intestine. Vulva at about 68% of body length. Demanian system well developed, located on the right side of the intestine. Spinneret as in male.

Diagnosis and discussion. Oncholaimus xiamenense sp. n. most closely resembles O. balli Nicholas & Stewart 1984 and O. sahariensis Coomans & Heyns 1983 . However, it can be distinguished from these two species by several characteristics. O. xiamenense sp. n. differs from O. balli by the pronounced sexual dimorphism in tail shape (tail shape is similar in both sexes in O. balli ), the lower number of circumanal genital setae (12 vs. 16) and the posterior location of the postcloacal tubercle (3/4 distance from cloaca to tip of tail vs. 2/3) ( Nicholas & Stewart 1984). O. xiamenense sp. n. is similar to O. sahariensis in many ways, such as body length and shape, cephalic setae length, spicule shape and length (44–52 µm vs. 47.5 µm), the pronounced sexual dimorphism in tail shape, the presence of a single postcloacal tubercle, the position of the testis. However, some differences can be seen. The most prominent feature is the more posterior positions of the excretory pore (88–112 µm from anterior end vs. 68.5µm) and ventral tubercle (3/4 from cloaca to tip of curved tail vs. just posterior to the middle of the tail); the whole female ovary as well as the demanian system is located on the right side of the intestine, while the reproductive system is to the left in O. sahariensis . In addition, morphometric values of the two species also show distinct gaps. The tail in male of the newly described species is relatively longer (c = 37.1–42.3 vs. 44.5–50), amphids are larger (amphid diameter 9 –11 µm vs. 7.5µm) and further from the anterior end (18–21 µm vs. 15.5–16.5 µm), buccal cavity is smaller (depth 27–32 µm vs. 34 µm and width 12–15 µm vs. 17–19 µm), genital setae fewer (12 vs. 16), and nerve ring (at 21–26% of pharynx length vs. 39% of pharynx length) and vulva (V = 68% vs. 70.9–73.8%) located relatively more anteriorly ( Coomans & Heyns 1983).

Figures

FIGURE 3. Oncholaimus xiamenense 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.