Onepunema enigmaticum

Leduc, Daniel & Verschelde, Dominick, 2013, One new genus and two new free-living nematode species (Desmodorida, Desmodoridae) from the continental margin of New Zealand, Southwest Pacific Ocean, Zootaxa 3609 (3), pp. 274-290 : 278-283

Onepunema enigmaticum gen. et sp. n.

( Figs 1–4 , Table 1 )

Measurements. See Table 1 .

Type specimens. Holotype male, collected 19 April 2007 (NIWA cruise TAN0705, station 196), northeastern Chatham Rise (42.615° S, 178.338 W), water depth: 1194 m, sediment depth: 0–5 cm, silt/clay content: 32.2%, CaCO3 content: 59.9%, sediment chlorophyll a concentration: 34 ng /gDW sediment (NIC 865968).

Species Onepunema enigmaticum gen. et sp. n. Pseudonchus virginiae sp. n. Males Female Male Female *At level of amphid.

Paratypes. One male, collected 16 April 2007 (NIWA cruise TAN0705, station 157), northeastern Chatham Rise (42.782° S, 176.715° W), water depth: 1029 m, sediment depth: 0–1 cm, silt/clay content: 37.5%, CaCO3 content: 61.6%, sediment chlorophyll a concentration: 7 ng /gDW sediment (UGMD 104261). One paratype male and one paratype female, collected 6 June 2007 (NIWA cruise TAN0707, station 99), eastern Challenger Plateau (40.126 ° S, 170.222° E), water depth: 804 m, sediment depth: 0–5 cm, silt/clay content: 83.3%, CaCO3 content: 68.8%, sediment chlorophyll a concentration: 15 ng /gDW sediment (NIC 865969). One paratype female, collected 5 October 2001 (NIWA cruise TAN0116, station U2582A), Chatham Rise crest (43.433° S, 178.500° E), water depth: 350 m, sediment depth: 0–5 cm, silt/clay content: 33.0%, CaCO3 content: 40.5%, sediment chlorophyll a concentration: 185 ng /gDW sediment (NIC 865970).

Etymology. The species name is derived from the Latin word aenigma (= something obscure, inexplicable), because this species possesses an unusual combination of traits and some of its characters are unclear or indistinct.

Description. Males. Cylindrical body, orange colour, tapering slightly towards both extremities. Cuticle thick with coarse annuli, no lateral differentiation. Distinct longitudinal rows of pores. Somatic setae unclear or hardly distinguishable in pharyngeal region, and absent along the rest of the body except for tail region where two pairs of pre-, one pair of para-, and one pair of postcloacal somatic setae are present. Two subventral and two subdorsal rows of pores with conspicuous ducts extending from posterior edge of amphid to tail tip, and four additional rows of pores, two ventrosublateral and two dorsosublateral, also present in pharyngeal region. Each pore connected to a single gland ( Figure 2 B).

Striated head capsule with fine groove (sutura) in the cuticle separating lip region from main head region. Striations can give a false impression of the presence of annuli on head capsule, but striations do not run all the way through the thick inner layer of the cuticle. One striation runs around amphid, giving false impression of amphideal plate. Labial region folded inwards in holotype and one paratype, extended in one paratype specimen. Cuticle of main head region conspicuously thicker than lip and somatic regions, striations extend from anterior edge of amphideal aperture. Six setiform outer labial sensillae on labial region and four slightly shorter cephalic setae at level of sutura. Outer labial sensillae and cephalic setae very close to each other. Inner labial sensillae not observed. Subcephalic setae absent. Large cryptospiral amphideal fovea located on main head region, surrounded by fine line in outer cuticle. Smaller circular amphideal aperture. Protruding corpus gelatum, long and narrow in shape. Body annuli extend from the posterior edge of amphideal aperture to the non-annulated tail tip.

Buccal cavity small, teeth not observed. Ducts extending from head sensillae towards nerve ring sometimes conspicuous, dark orange in colour. Pharynx muscular, narrow, may be bent, with well-defined, rounded pharyngeal bulb. Nerve ring at 50–60% of pharynx length. Secretory-excretory system not observed. Cardia short. Intestinal epithelium consists of at least two types of cells (heterocytous); the first, most common type of cell only slightly stained by Rose Bengal, second type heavily stained. Both cell types contain numerous round inclusions, 1–2 Μm in diameter ( Figure 4 D).

Reproductive system diorchic with two short testes, 53–63 Μm long, outstretched and opposed. Position of testes within body cavity difficult to ascertain; appear to be located either both on the left of intestine, both on the right of intestine, or with anterior testis to the left and posterior testis to the right of intestine in the respective specimens examined. Mature sperm small, globular, 2–4 Μm in diameter. Short, arcuate spicules with central cuticularised projection present along entire length of spicules, with discontinuity at level of capitulum; velum present ( Figure 1 D). Complex arcuate gubernaculum proximally surrounding spicules, with broad cuneus and lateral crurae ( Figure 1 D, F). Four or five pre-cloacal supplements consisting of thickened areas of cuticle. Two pairs of pre-, one pair of para- and one pair of postcloacal somatic setae. Tail conical with three caudal glands and clear spinneret.

Female. Similar to males, but with greater body diameter and slightly smaller amphideal aperture. Labial portion of head capsule extended in one specimen. Arrangement and structure of labial sensillae similar to males, but in one specimen right lateral outer labial sensilla is situated close to right laterodorsal cephalic seta instead of being located laterally ( Figure 4 A). Female reproductive system didelphic, amphidelphic with reflected ovaries. Position of ovaries difficult to ascertain; in one specimen appear to be located ventrally, in the other to the right of intestine. Vulva located slightly pre median. Cuticular pars distalis vaginae and pars proximalis vaginae surrounded by constrictor muscle.

Diagnosis. Onepunema enigmaticum gen. et sp. n. is the type species of Onepunema gen. n. Onepunema enigmaticum gen. et sp. n. is characterised by the presence of two laterodorsal and two lateroventral rows of pores with conspicuous ducts, slender pharynx with rounded terminal bulb, presence of two types of cells in intestinal epithelium. Males are characterised by the presence of four or five pre-cloacal supplements consisting of thickened areas of cuticle.

Differential diagnosis. Onepunema enigmaticum gen. et sp. n. resembles some species of the genus Chromaspirina , such as C. pontica Filipjev, 1918 and C. parapontica Luc & De Coninck, 1959 in shape of body and head region, but can easily be distinguished from them as these species all have distinct teeth in their buccal cavity (absent in Onepunema enigmaticum gen. et sp. n.) and distinct somatic setae (absent along the body in Onepunema enigmaticum gen. et sp. n.). Onepunema enigmaticum gen. et sp. n. resembles Spirinia parasitifera (Bastian, 1865) in the small buccal cavity and shape of the spicules, but can be distinguished from it as S. parasitifera has papilliform outer labial sensillae, unispiral amphids, obvious somatic setae and slender body annuli. Onepunema enigmaticum gen. et sp. n. resembles Spirinia schneideri Luc & De Coninck, 1959 in head and buccal cavity shape, but can be distinguished from it as S. schneideri has unispiral amphids and a very short, blunt tail. Zalonema myrianae Verschelde & Vincx, 1996 is similar to Onepunema enigmaticum gen. et sp. n. in the shape of the head capsule and buccal cavity with inconspicuous teeth, but differs from the latter in the presence of cheilorhabdia (not observed in Onepunema enigmaticum gen. et sp. n.), and subcephalic setae (absent in Onepunema enigmaticum gen. et sp. n.), and multispiral amphideal fovea (cryptocircular in Onepunema enigmaticum gen. et sp. n.).

Figures

FIGURE 1. Onepunema enigmaticum gen. et sp. n. A: head region, surface view; B: detail of fovea- (outer line) and amphideal aperture (inner line); C: head region, cross-section view; D: cloacal region with right spicule, gubernaculum, and pre-, para- and post-cloacal setae; E: right spicule; F: left spicule and gubernaculum; G: gubernaculum, right hand side view; H: gubernaculum, left hand side view. Scale bar = 20 Μm.

FIGURE 2. Onepunema enigmaticum gen et sp. n. A: Male anterior region; B: male anterior region showing amphideal aperture and position of glands and pores; C: female anterior region. Scale bar = 35 Μm.

FIGURE 3. Onepunema enigmaticum gen. et sp. n. A: Entire male in cross-section view showing position and arrangement of testes; B: posterior male region, showing spicules and pre-cloacal supplements; C: female reproductive system; D: female tail, with details of glands and pores. Scale bar: A = 60 Μm; B and C = 30 Μm; D = 20 Μm.

FIGURE 4. Onepunema enigmaticum gen. et sp. n. Light micrographs. A: Right lateral view of female head, showing unusual arrangement of head sensillae, cuticle annulations, and circular amphideal aperture; B: cross-section view of female head, showing thickened cuticle of main head region, reduced buccal cavity, and extended labial region; C: male mid-body region showing anterior (top) and posterior (bottom) testes; D: cross-section view of male middle body region, showing two types of cells in intestinal epithelium with numerous round inclusions; E: spicule. Arrows point towards the testes. Scale bar: A and B = 10 Μm; C = 35 Μm; D = 20 Μm; E = 16 Μm.

Tables

TABLE 1. Morphometrics (Μm) of Onepunema enigmaticum gen. et sp. n. and Pseudonchus virginiae sp. n. (a, body length / maximum body diameter; abd, anal body diameter; b, body length / pharynx length; c, body length / tail length; cbd, corresponding body diameter; V, vulva distance from anterior end of body; % V, V / total body length).

	Holotype	Paratypes	Paratypes	Holotype	Paratype
n		2	2
L	1184	844–882	859–1055	1206	1110
a	33	26–29	23–25	20	13
b	8	8	8–9	8	8
c	15	11	11–13	18	16
Head diam.*	18	14–15	14–15	18	19
Length of outer labial sensillae	3	2–3	2	1	1-2
Length of cephalic setae	2	2	2	2	3
Amphid height	10	7–9	9	12	8
Amphid width	10	9	9	11	9
Amphid width/cbd (%)	55	60–64	60-–64	38	26
Amphid from anterior end	5	3–4	3–6	15	19
Nerve ring from anterior end	72	53–58	67–69	95	85
Nerve ring cbd	33	28–30	30	48	47
Pharynx length	122	104–107	102–121	150	135
Pharynx cbd	36	30–33	32–34	53	57
Pharyngeal bulb diam.	26	21–23	23–25	30	37
Max. body diam.	36	30–33	35–45	60	83
Spicule length	40	30–38	-	55	-
Gubernaculum length	20	14–15	-	24	-
Anal body diam.	32	26–27	25	44	39
Tail length	80	77–78	79–83	66	69
Tail length/abd	2.5	2.9–3.0	3.2–3.3	1.5	1.8
V	-	-	356–484	-	690
%V	-	-	41–45	-	62
Vulval body diam.	-	-	35–45	-	83