Paroctonchus nanjiensis, Shi, Benze & Xu, Kuidong, 2016

Shi, Benze & Xu, Kuidong, 2016, Paroctonchus nanjiensis gen. nov., sp. nov. (Nematoda, Enoplida, Oncholaimidae) from intertidal sediments in the East China Sea, Zootaxa 4126 (1), pp. 97-106 : 99-104

Paroctonchus nanjiensis gen. nov., sp. nov.

(Figs 2, 3, 4; Table 1 )

Diagnosis. Body length 3516–4750 µm. Six lips with six inner labial papillae. Six outer labial setae and four cephalic setae in one circle, equal in length. Buccal cavity armed with one very large left ventrosublateral tooth, one right ventrosublateral and one dorsal tooth of medium-size, and about 27 small teeth distributed on the wall of buccal cavity. Amphidial fovea pocket-like with transverse slit-like aperture, in middle portion of buccal cavity. Cardia conspicuous and conical. Dorsolateral and ventrolateral orthometanemes not observed. Two ovaries opposed and reflexed. Demanian system absent. Two testes opposed and outstretched. Spicules short and straight without gubernaculum. About 10 wart-like precloacal supplements in two subventral rows. Tail conical-cylindrical.

Type material. Holotype: one male on slide NJ-20140513-93. Paratypes: four males on slides NJ-20140513- 23, -31 and -92, and two females on slides NJ-20140513-31 and -73, and one juvenile on slide NJ-20140513-92. All type slides have been deposited in the Marine Biological Museum of the Chinese Academy of Sciences.

Type locality. Intertidal sandy sediment in the Dasha’ao Beach of the Nanji Islands in the East China Sea (27°27'46"N, 121°3'29"E). The temperature of interstitial water was 22°C and salinity at 28 psu during sampling. The median particle diameter of sediment was about 612 µm (coarse sand) and sediment organic matter content was about 2.5%.

Etymology. The species name is derived from the type locality where the new species was discovered: the Nanji Islands.

Measurements. See Table 1 .

Description. Body length 3516–4750 µm. Cuticle smooth. Six rounded lips with six inner labial papillae. Six outer labial setae and four cephalic setae in one circle, equal in length (Figs 2A–D, 3A–C). Buccal cavity large and spacious, with wall strongly sclerotized and only posterior end surrounded by pharyngeal tissue (Figs 2A–D, 3A– C, E). Three typical oncholaimid teeth composed of one dorsal and two ventrosublateral large teeth, with the left ventrosublateral tooth apparently the largest and the right ventrosublateral tooth slightly larger than the dorsal one; about 27 additional small teeth (or denticles) distributed on the wall of buccal cavity (Figs 2A–D, 3A–C, E). Amphidial fovea pocket-shaped with transverse slit-like aperture, situated in middle portion of buccal cavity (Figs 2A–D, 3D, E). Six subcephalic setae at the base of buccal cavity. Cervical setae roughly in four longitudinal rows FIGURE. 2. Paroctonchus nanjiensis gen. nov., sp. nov. A, B, E, F: Anterior and posterior region of the male holotype, showing the strongly sclerotized and spacious buccal cavity with the posterior end surrounded by pharyngeal tissues, a dorsal and a pair of ventrosublateral teeth and many small teeth, the many precloacal supplements, two stout setae at the cloacal region, the short and straight spicules, the conical-cylindrical tail and caudal setae; C, D: Anterior region of a female paratype, showing the same structures as the male holotype; G, H: Posterior region of the same female paratype, showing the reflexed ovaries, three caudal glands and the conical-cylindrical tail. Scale bars: 30 µm.

at pharyngeal region (Figs 2A–D, 3D). Pharynx cylindrical with smooth outline (Figs 2A–D, 3A–C, E). Nerve ring at approximately the anterior third of pharynx. Cardia conspicuous and conical (Fig. 2A, C). Excretory pore not observed. Three caudal glands, with cells extending 60–130 µm anterior to cloaca. Spinneret present. Tail conicalcylindrical. Dorsolateral and ventrolateral orthometanemes not observed.

Male. Two opposed and outstretched testes situated on right side of intestine. Spicules short and straight, dagger-shaped (Figs 2E, F, 3G). Gubernaculum absent. About ten wart-like precloacal supplements in two subventral rows (Figs 2E, 3F, G). Two thick, relatively short subventral setae present in cloacal region (Fig. 2E, F). Posterior region of male strongly bent ventrally. Tail composed of anterior conical half and posterior cylindrical half, with several setae at cylindrical region and four subterminal setae (Figs 2E, F, 3H). Tail tip slightly swollen.

Female. Two opposed and reflexed ovaries on right side of intestine (Figs 2G, 4A, C). Vulva transverse slitlike, situated at 64.4–64.9% of body length; vagina short and muscular, with many small glandular cells around (Figs 2G, 4B). Uterus indistinct. Demanian system not observed. Tail composed of conical anterior third and cylindrical posterior two thirds, with only four subterminal setae (Figs 2H, 4D).

Juvenile. Only one juvenile specimen was observed. Body length about 2146 µm, much shorter and stouter than adults (a about 53.7 vs. 81.1–96.9), with relatively longer tail (c about 16.5 vs. 32.3–34.2, c’ about 4.5 vs. 3.1– 3.7). Buccal cavity structure and the pattern of teeth similar to that of adults, but with only about 20 teeth including three large oncholaimid teeth ( Fig. 5 A, B).

Figures

FIGURE 5. Juveniles of Paroctonchus nanjiensis sp. nov. (A, B), Octonchus marinus (C, D), Patagonema iubatum (E, F) and four representative genera / subfamilies of the families Oncholaimidae (G – I) and Enchelidiidae (J). A, B: Juvenile of Paroctonchus nanjiensis sp. nov. with three large teeth and many additional small teeth and a conical-cylindrical tail; C, D: Juvenile of Octonchus marinus with one large tooth and eight small teeth and a conical tail (after Schulz 1932); E, F: Juvenile of Patagonema iubatum with three large teeth and three mandibular ridges with small teeth (after Pastor de Ward et al. 2015); G: Oncholaimelloides, representing the subfamily Oncholaimellinae, typically with three teeth: one large and two slightly smaller teeth (after Murphy 1966); H: Eurystomina, representing the family Enchelidiidae, with three teeth and many denticles (after de Man 1907); I: The three teeth are either very small or absent in the subfamily Pelagonematinae, in which Phaenoncholaimus has a well-developed dorsal tooth and an inconspicuous left ventrosublateral tooth (after Kreis 1934); J: No teeth exist in Krampia of the subfamily Krampiinae (after Belogurov & Dashenko 1981).

Tables

TABLE 1. Morphometrics (measurements in µm) of Paroctonchus nanjiensis gen. nov., sp. nov.

Characters	Holotype	Paratypes
		Males (n=4)	Females (n=2)
Body length	4083	3892–4388 (4104)	4516–4750
Body length/maximum body diameter	86.9	81.1–87.8 (83.7)	86.8–96.9
Body length/pharynx length	6.2	5.9–6.4 (6.1)	6.5–6.7
Body length/tail length	34	32.3–34.2 (33.4)	32.5
Tail length / anal body diameter	3.3	3.1–3.5 (3.3)	3.5–3.7
Head diameter	39	39–40 (39.3)	40
Outer labial setae, length	18	16–17 (16)	16–17
Cephalic setae, length	18	16–17 (16)	16–17
Buccal cavity length	50	50–52 (51)	55
Buccal cavity width	24	23–27 (25)	27–28
Amphid from anterior end	30	25–35 (28)	30–33
Nerve ring from anterior end	242	250–265 (260)	251–268
Pharynx length	660	658–683 (673)	675–733
Maximum body diameter	47	48–50 (49)	49–52
Vulva from anterior end	–	–	2930–3058
Vulva from anterior end × 100/body length %	–	–	64.4–64.9
Spicule length	41	40–46 (42)	–
Cloacal body diameter	36	35–40 (38)	–
Anal body diameter	–	–	40–41
Tail length	118	118–130 (123)	139–146