Rhynchonema dighaensis, Datta, Tridip Kumar, Navarrete, Alberto De Jesus & Mohapatra, Anil, 2015

Datta, Tridip Kumar, Navarrete, Alberto De Jesus & Mohapatra, Anil, 2015, Rhynchonema dighaensis sp. nov. (Monhysterida: Xyalidae): a marine nematode from the Indian coast with an illustrated guide and modified key for species of Rhynchonema Cobb, 1920, Zootaxa 3905 (3), pp. 365-380 : 369-371

Rhynchonema dighaensis sp. nov.

Table 1 , Figs 3 , 4

Material studied. Seven males, three females. Glycerin slides.

Type material. Holotype male: Reg. No. MARC /ZSI/N3358, L: 650.9 µm. (Co-ordinates of the Collection Site: 21° 37′ 15′′ N; 87° 31′ 13′′ E)

Allotype female: Reg. No. MARC /ZSI/N3365, L:672.4 µm.

Male Paratypes: Reg. No. MARC /ZSI/N3359, L:506 µm; Reg. No. MARC /ZSI/N3360, L:602.6 µm; Reg. No. MARC /ZSI/N3361, L:606.5 µm; Reg. No. MARC /ZSI/N3362, L:534.4 µm; Reg. No. MARC /ZSI/N3363, L:540.5 µm; Reg. No. MARC /ZSI/N3364, L:551.1 µm

Female Paratypes: Reg. No. MARC /ZSI/N3365, L:648.5µm; Reg. No. MARC /ZSI/N3366, L:642.6 µm.

Habitat. Digha beach is siliciclastic, quartzofeldspathic in composition with well sorted, medium to fine sand ( Bhattacharya et al. 2003). The range of temperature, salinity and pH of sediment percolated water of the study location during April, 2012 are given below with average and standard deviation:

Temperature (°C): 31–32.5 (31.86±0.51)

Salinity (ppt): 24.3–28.1 (26.73±1.28)

pH: 7.9–8.25 (8.07±0.12)

Description. Males (Holotype and six paratypes) ( Figs 3 , 4 ): Body elongated, slender and tapering at both ends (L: 506–651 µm, mbd: 15–16 µm). Anterior region from the level of the amphid is beak-like. Buccal cavity 37–47 µm long, diameter of proximal being 4 µm and distal part 7 µm. Anterior end bears three pairs of outer labial sensilla 5 µm long, situated at one level corresponding to about one head diameter. Other sensilla not visble in light microscopic observation. Rows of somatic setae 10 µm long dispersed over entire body surface; not arranged in pairs. Amphid circular in shape, 4 to 5 µm in diameter. Entire body strongly annulated, with annules spaced approximately 1 µm apart. Twenty-three to twenty-six annules anterior to amphid. Amphid occupies 58–70% of corresponding body diameter. From the anterior end, first 30–40% of all annules are anteriorly directed; remaining 60–70% annules are posteriorly directed. Direction of annules changes at level posterior to distal part of oesophagus. No cuticular ornamentation observed. Oesophagus begins at the base of amphid, is 1/6 to 1/5 total body length. Oesophagus cylindrical, terminating with a moderate bulb. Cardia small, oval, doughnut-shaped, extending into the intestine more than half of its body. Nerve ring at 60% of the proximal part of oesophagus. Excretory pore not observed. Genital tracts paired and opposed, with anterior one lying to the left and posterior to the right side of intestine. abd is 14–16 µm. Tail narrows gradually, conoid,67–79 µm long; with terminal spinneret. Tail 6.8–8.5 times smaller than the total length and about 4.6–5.2 times bigger than abd. Spicules protruded from body when killed; slightly curved, pointed at distal end and asymmetric with left larger than right. Left spicule 19–29 µm long; right16–24 µm in length. Gubernaculum plate-like with dorsal apophysis. Dorsal apophysis symmetrical; proximal part of dorsal is wider and distal part is narrower; little curved at tip.

Females (Allotype and two paratypes) ( Figs 3 , 4 ): Entire body size, shape, structure and measurements of various body parts, except for female specific characters, similar to males. Body length 643–673 µm and mbd 16–17 µm. In comparison to male specimens, tails in females are shorter. Female genital system monodelphic, prodelphic and outstretched; occupying 41–44% of body length. It lies left of intestine and it occupies 61–64% of the head to vulva body length. Vulva is flanked by two ovoid, flap-shaped cuticular structures, arising laterally to the vulval slit. Vulva at 67–70% of body length.

Diagnosis. Rhynchonema dighaensis sp. nov. is about 650 µm long; it has characteristically arcuate and pointed spicules with a bulbous proximal end; unequal in size with left spicule larger than right; gubernaculum plate-like; caudal apophysis of gubernaculum symmetrical; buccal cavity less than 50 µm long; twenty-three to twenty-six annules present anterior to circular amphid; cuticle non-ornamented with fine hairs over the entire body.

Etymology. The species name dighaensis refers to the name of the collection locality Digha, West Bengal, India.

TABLE 2. Comparative morphometrics of species of the genus Rhynchonema Cobb, 1920 . Smaller spicules are indicated within brackets.

Figures

FIGURE 3. Habitus of A) Holotype male, B) Allotype female. Arrows indicate the changes in orientation of body annules, C) Buccal cavity and position of amphid in holotype, D) Flap at vulval region in Allotype female, E) Spicules and gubernaculum of holotype male.

FIGURE 4. Photomicrograph of A) Holotype whole body, B) Allotype whole body, C) male head, D) male copulatory apparatus (spicules at different focus), E) vulval flap and tail in allotype female.

Tables

TABLE 1. Morphometric measurements of Rhynchonema dighaensis sp. nov.

	Male (n=7)		Female (n=3)
Characters states	Holotype	Range (Mean±SD)	Allotype Range (Mean±SD)
L	650.9	506.0–650.9 (570.3±50.9)	672.4 642.6–672.4 (654.5±15.8)
mbd	16	15.0–16.0 (15.5±0.4)	16.9 16.3–16.9 (16.5±0.3)
O	125.9	93.1–125.9 (105.2±12.0	128.3 128.3–128.5 (128.4±0.1)
T	79.1	67.6–79.1 (72.2±3.8)	66 65.9–77.2 (69.7±6.5)
abd	15.2	14.2–15.2 (14.9±0.5)	13.5 12.7–13.5 (13.1±0.4)
bl	39.4	37.2–42.6 (40.1±2.2)	40.9 40.5–41.6 (41.0±0.6)
bd px	4.2	4.2–4.2 (4.2±0)	4.2 4.2–4.2 (4.2±0)
bd pa	7.3	7.3–7.3 (7.3±0)	7.3 7.3–7.3 (7.3±0)
ad	5.1	4.2–5.2 (4.8±0.4)	5.2 4.7–5.2 (4.9±0.3)
ls	5.2	5.2–5.2 (5.2±0)	5.2 5.2–6.2 (5.9±0.6)
ss	10.4	10.4–10.4 (10.4±0)	10.4 10.4–10.4 (10.4±0)
an	23	23–26 (24.9±1.5)	26 26–26 (26.0±0.0)
hv	–	–	471.6 433.9–471.6 (453.3±18.9)
S lft	22.5	18.7–29.2 (22.6±3.7)	– –
S rgt	21.5	16.1–24.1 (20.1±2.9)	– –
G	7.3	5.2–7.3 (6.2±0.8)	– –
ap	3.1	3.1–6.2 (4.8±1.0)	– –
a	40.6	33.6–40.6 (36.7±2.5)	39.8 39.1–39.8 (39.6±0.4)
b	5.2	5.1–6.1 (5.4±0.3)	5.2 5.0–5.2 (5.1±0.1)
c	8.2	6.8–8.5 (7.9±0.6)	10.2 8.3–10.2 (9.5±1.0)
cʹ	5.2	4.6–5.2 (4.9±0.3)	4.9 4.9–6.1 (5.3±0.7)
V	–	–	70.1 67.5–70.1 (69.2±1.5)
Vʹ	–	–	77.8 76.7–78.0 (77.5±0.7)