Polkepsilonema arabicensis, Datta & Rajmohana, 2020

Datta, Tridip Kumar & Rajmohana, Keloth, 2020, A new free-living marine nematode, Polkepsilonema arabicensis sp. n. (Desmodorida: Epsilonematidae), from Lakshadweep, India, Zootaxa 4722 (4), pp. 371-380 : 373-377

Polkepsilonema arabicensis sp. n.

( Figs 2–4 , Table 1 )

Material examined. Two adult males, one adult female and three juvenile (females) on glycerine slides . Holotype male: Reg. No. WN2690 . Male paratype: Reg. No. WN2691 . Female paratype (adult): Reg. No. WN2692 . Female paratype (juvenile): Reg. No. WN2693; Reg. No. WN2694; Reg. No. WN2695

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Type habitat. Samples were collected from the coralline intertidal sand of Agatti island , Lakshadweep, India, 10°52.694ˈN, 72°12.143ˈE. Collector. Dr. (Mrs.) Keloth Rajmohan, Date: 22 nd November 2017.

Etymology: The genus Polkepsilonema is recorded for the first time from the ‘Arabian’ (latin ‘Arabica’) sea and specific epithet denotes the part of the type locality near India.

Description. Body typically ‘Ɛ’-shaped, well less than 1 mm, tapered at both ends; body sections along the pharynx and reproductive system were wider than the section inbetween. Annuli, 110 to 123 in numbers, present throughout body with exception of head capsule and tail end. Cuticular annuli thick and ornamented with one row of vacuoles from first body ring and arranged in roof-tile like overlapping pattern. Annuli ornamentation heterogeneous. Body with two curvatures: anterior curvature i.e. dorsal curvature, and posterior curvature i.e. ventral curvature. Annuli forwardly directed at anterior curvature of body and after that inversely directed. Annulation with irregular anastomoses; number of anastomoses increased specially at the curvatures. Annular ridges present between vacuoles and appeared in form of spiky epicuticle at posterior edges. Degree of overlapping of body annuli increases at curvatures. Body covered with mucus and occasionally found with adhered particles.

Six protrusible lips without sensilla. Cephalic capsule (rostrum) conical, four cephalic sensilla submedian in position. Cephalic capsule with 14 subcephalic sensilla of which 10 are located anterior to amphids. In lateral view general arrangement of subcephalic sensilla as follows: i) two subcephalic sensilla closely located to each other found just posterior to denticles at midlateral surface (in juveniles one of these sensilla is either lost or smaller in length, appearing as minute sensilla 1–2 µm in length; origin of sensilla were identified by their markings on cephalic capsule); ii) second group of two sensilla found at subdorsal and subventral surfaces posterior to first group; iii) fifth sensillum located just above or near anterior margin of amphid; iv) sixth and seventh sensilla located at laterodorsal and lateroventral surface of the body. Amphids sub-dorsally positioned. Amphideal fovea sexually dimorphic. Cephalic sensilla 1.1–1.3 times of cephalic diameter at level of insertion. Somatic setae present subdorsally and subventrally.

Stoma with one dorsal and two ventrosublateral denticles. Pharynx muscular and clearly divided in two parts; corpus of pharyngeal region narrow and typically bent anterior to nerve ring; postcorpus forms dilated bulb region with sclerotized lumen wall. Nerve ring located 56%–60% of the length of pharynx from anterior end. Cardia, secre- tory-excretory system indiscernible.

Fine setae like spines at curvatures of body found in most of specimens including holotype.Ambulatory setae of two types: i) ventral field of bisinuous or double-bent setae (14–15 µm) with inwardly curved end, ii) straight subventral setae (15–16 µm), distally bent, present at each lateral side of bisinuous setae guarded by very short setae; short setae more numerous along ventral and ventrolateral surface than dorsal. Bisinuous setae in 5–6 longitudinal rows located (sub)ventrally at anterior part of ventral curvature. Straight ambulatory setae extend posteriorly to the level of double-bent ambulatory setae. Tail region having six annuli and non-annulated tip; annulated tail region with both subventral and subdorsal setae; non-annulated region heavily cuticularized, without setae.

Male (Adult). Fovea amphidialis interrupted loop shaped, aperture amphidialis with spatulated flap. Reproductive system monorchic with outstretched testis; located left to intestine; extended up to anterior body curvature. Vas deferens broad and long. Spicules paired and arcuate; capitulum club shaped; lamina with thin vellum. Gubernaculum thin, plate shaped, 18–19% of spicule length measured along arc (26% if measured along chord). Cloacal opening guarded by two small somatic setae followed by one comparatively longer somatic seta. Copulatory thorns, different in size, located ventrally in two clusters or groups; first group having four large thorns with length of 2.5–6 µm; first two thorns lie parallel very close to each other; these thorns preceded by two minute spines with length of 1–1.5 µm; second group of two thorns with length of more than 4 µm is located 10–20 µm posterior; none of copulatory thorns of second group connected with ambulatory setae. Stout somatic setae, three in number, present near the second group of copulatory thorns. Straight ambulatory setae 4–5 in number.

Female (Mature). Body shape, annulation number, pattern, ornamentation, number of cephalic and subcephalic setae are similar to male. Fovea amphidialis spiral (1.25 turn), aperture amphidialis with central spot. Straight ambulatory setae six in number and extended posterior to vulva region. No setae posterior to anal opening. Bisinuous ambulatory setae located in-between ventral body curvature and posterior region of vulval opening. Vagina short, tripartite. Reproductive system didelphic, amphidelphic; anterior and posterior ovaries reflexed left and right to intestine respectively. Vulva transverse, cuticle around vulva slightly dilated; pars proximalis vaginae connected with uteri, pars refringens vaginae elongate, dark brown in colour and connected with muscles; pars distalis vaginae very small, located to the outside of pars refringens vaginae. Ventral field of copulatory thorns absent.

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Female (4th stage juvenile). Subcephalic sensilla vary from 12–14 in number. Body annuli, body diameter, cephalic and subcephalic sensilla, position of nerve ring, pharynx length, ambulatory setae etc. similar to adults. Amphideal fovea female specific, spiral type. Reproductive system not developed and associated structures inconspicuous.

Diagnosis. Polkepsilonema arabicensis sp. n. typically ‘epsilon’ shaped with length less than 600 µm. Cephalic capsule bears 14 subcephalic sensilla of which 10 are anterior to amphids. Males are with interrupted loop shaped amphideal fovea while females have spiral amphideal fovea. Fine spines present at both dorsal and ventral curvature of body. Bisinuous ambulatory setae in 5–6 rows on ventral surface of the body guarded by one row of straight setae with curved end at each lateral side. Straight setae supported by small setae. Male with two clusters of copulatory thorns: anteriormost cluster with four large and two minute thorns and posterior cluster with two thorns. Two short setae near cloacal opening. Male with curved spicules (41–47 µm along arc) with flat boat-shaped gubernaculum. Tail with six body annuli and non-annulated cuticularized tip.

Figures

FIGURE 2. Polkepsilonema arabicensis sp. n. habitus of a) holotype male (WN2690) and b) paratype female (WN2692). Anterior end of c) holotype, d) paratype female (WN2692) and e) juvenile paratype (WN2694). f) spicule, gubernaculum (lateral view) and tail of holotype, g) copulatory thorns of holotype, h) & i) fine setae at 1st and 2nd body curvatures, j) vulval morphology. ppv: pars proximalis vaginae, prv: pars refringens vaginae. Scale bar: a & b = 50 µm, c–j = 10 µm.

FIGURE 3. Polkepsilonema arabicensis sp. n. photomicrographs of a) holotype male, b) paratype female (WN2692), c) paratype female (WN2693); holotype d) spicule & e) gubernaculum (lateral view); f) cuticular anastomoses; g) cuticular structure and spines at body curvatures of holotype; h) straight ambulatory setae marked with arrows of holotype; i) copulatory thorns of paratype male (WN2691); j) dorsal and ventrosublateral teeth of paratype (WN2694); k) hyaline outer layer as spiny projections at curvature level of paratype (WN2695); l) straight ambulatory setae of paratype (WN2695); m) copulatory thorns of holotype; n) bisinous ambulatory setae of paratype (WN2693). Scale bar: a & b = 50 µm, c = 20 µm, d–n = 10 µm.

FIGURE 4. Polkepsilonema arabicensis sp. n. photomicrographs of the cephalic capsule of a) holotype, b) paratype (WN2693), c) paratype (WN2694); d) paratype (WN2695); e) & f) paratype male (WN2691) at different focus. Scale bar: a–f = 10 µm.

Tables

TABLE 1. Morphometrics of Polkepsilonema arabicensis sp. n. collected from Agatti island, Lakshadweep, India. All the characters except ratios are given in μm

Registration No.	WN2690	WN2691	WN2692	WN2694	WN2693	WN2695
Type	Holotype (♂)	Paratype1 (♂)	Paratype1 (♀)	Paratype3 (♀) Juvenile	Paratype4 (♀) Juvenile	Paratype2 (♀) Juvenile
Total Length	537	415	466	458	358	398
Number of body annules	122	113	119	123	111	110
Length of cephalic sensilla	12	9	12	10	8	9
Pharynx length	96	94	92	90	84	94
Tail length	44	37	38	39	33	36
Non-annulated head length	19	18	19	20	18	17
Non-annulated tail length	18	17	17	16	15	16
Spicule length (arc)	41	47	NA	NA	NA	NA
Spicule length (chord)	29	33	NA	NA	NA	NA
Gubernaculum length	9	9	NA	NA	NA	NA
Length of bisinous ambulatory setae	14	14	14	14	15	15
Length of straight ambulatory setae	15	15	15	15	16	16
Amphid fovea width	6	5	5	4	5	5
Cephalic diameter at the level of cephalic sensilla	10	8	9	8	7	7
Body diameter at amphid fovea	17	16	17	15	13	16
Body diameter at pharynx base	34	34	37	41	35	35
Anal body diameter	24	28	24	24	19	24
Diameter at vulva level	0	0	49	47	?	49
Maximum body diameter	37	38	49	47	37	49
Amphid fovea distance from anterior end	14	12	15	16	13	14
Distance from anterior end to nerve ring	58	53	52	52	50	53
Distance from anterior end to vulva	0	0	316	363	?	264
Cephalic sensilla length to cephalic diameter at the level of insertion	1.2	1.1	1.3	1.2	1.1	1.2
Position of nerve ring with respect to pharynx length from anterior end (%)	60	56	57	58	60	56
a	14.5	10.9	9.5	9.7	9.6	8.1
b	5.6	4.4	5.1	5.1	4.3	4.2
c	12.2	11.1	12.3	11.6	10.7	10.9
c’	1.9	1.3	1.6	1.7	1.8	1.5
V	0	0	67.7	79.2	?	66.2
V’	0	0	73.7	86.6	?	72.8