Distolabrellus magnivulvatus, Abolafia, Joaquín & Peña-Santiago, Reyes, 2011

Abolafia, Joaquín & Peña-Santiago, Reyes, 2011, Description of Distolabrellus magnivulvatus sp. n. (Nematoda, Rhabditida, Mesorhabditidae) from Iberian peninsula, the second species of a rare genus, Zootaxa 2804, pp. 56-64 : 57-63

Distolabrellus magnivulvatus sp. n.

( Figs 1–3 , 4 B)

Measurements. Table 1 .

Character Holotype Paratype females Paratype males

female Mean ± S.D. (range) Mean ± S.D. (range) Description. Adult: Small to medium-sized nematodes, 0.65–1.07 mm long. Body cylindrical, tapering towards both ends, but more so towards the posterior conical tail. Habitus almost straight upon fixation, curved ventrad in posterior body region in males. Cuticle bearing very fine transverse and longitudinal striations, tessellated. Lateral fields with three longitudinal incisures (two ridges). Lip region almost continuous with, although slightly wider than, adjacent body. Oral opening circular, surrounded by a thick, smooth, ring-like area. Lips six, separated and dimorphic: one subdorsal, one lateral and one subventral more developed, extending to cover or hang over oral opening; the other lips more reduced, conoid and lacking distinct extensions over oral aperture. Cephalic papillae distinct, button-like. Amphidial apertures pore-like to oval. Stoma rhabditoid, 2.0–2.8 times the lip region dismeter in length: cheilostom lacking refractive rhabdia; buccal tube (gymnostom plus promesostegostom) with straight rhabdia; gymnostom just longer than promesostegostom; telostegostom with more or less symmetrical glottoid apparatus, bearing three setose denticles. Pharynx typically rhabditoid, 126–162 μm long, consisting of three sections: a pharyngeal corpus differentiated into a cylindrical anterior procorpus about three times the length of the metacorpus, and a swollen, ovoid, posterior metacorpus with refractive lining; an isthmus almost as long as procorpus; and a pyriform basal bulb, with a grinder. Numerous small cells surround the isthmus-basal bulb junction in some specimens. Nerve ring at 68–79% of distance to pharyngo-intestinal junction, at level of isthmus. Excretory pore at 71–95% of distance to pharyngo-intestinal junction, at level of the anterior part of basal bulb, rarely more anterior; excretory duct with refractive walls close to excretory pore. Deirid situated 87–93% of distance to pharyngo-intestinal junction, at level of basal bulb or cardia, poorly visible. Cardia conoid, surrounded by intestinal tissue. Intestine tubular, lacking any differentiation.

Female: Reproductive system monodelphic prodelphic. Ovary reflexed dorsally. Oviduct tubular, frequently with oocytes. Uterus a long tube, rarely containing eggs of 28 x 89 μm. Vagina thin-walled, short. Vulva very posterior, aperture transverse with protruded lips, forming an elevated vulval cone; cuticle of anterior lip seeming to be sloughed off to partially cover surface. Anterior and posterior to vulval cone the body cuticle appears distinctly differentiated, forming a short longitudinal fold. Distance from vulva to anus 1.7–2.4 times the tail length. Rectum 1.0–2.0 times the anal body diameter long. Tail conical, with finely rounded tip. Phasmid at 12–21% of tail length.

Male: Reproductive system monorchic, with dorsally reflexed testis and a two lateral sacs at ejaculatory duct. Anterior lip of cloacal aperture with a short projection bearing a papilla. Tail conical, somewhat concave ventrally. Bursa peloderan, open anteriorly, margins almost parallel to body axis, bearing ten pairs of genital papillae (2+1/ 4+3): three pre-cloacal (two together at level of spicule lamina, one single near the cloaca aperture) and seven postcloacal (four grouped at mid-length of tail, three grouped near tail tip). Phasmids not well observed. Spicules 2.3– 3.1 times anal body diameter long, 1.5-2.0 times gubernaculum length, fused for two-thirds length, manubrium rounded or slightly lobed, calamus narrow and long, and lamina almost straight, thinner at its distal part and more or less bent dorsad at the tip. Gubernaculum almost straight, fusiform, 1.3–1.9 times as long as anal body diameter.

Diagnosis. The new species is characterized by its 0.89–1.07 mm long body in females and 0.65–0.99 mm in males, cuticle tesselated, lateral fields with three longitudinal incisures, lip region almost continuous and 10–13 µm wide, lips alternately dimorphic (three extremely reduced and three ovoid), stoma 22–30 Μm long or 2.0–2.8 times the lip region diameter, pharyngeal collar shorter than half of total stoma length, pharyngo-intestinal junction 148– 190 µm from anterior, V = 82–86, vulva a transverse slit located in a vulval cone and with its anterior lip bearing a flap-like structure, body cuticle surrounding the vulva especially differentiated, female tail conical with acute tip (68–90 Μm, c = 10.9–14.6, c’ = 2.1–4.5), male tail conical (23–32 Μm, c = 24.8–34.0; c’ = 1.0–1.4), bursa peloderan and open anteriorly, genital papillae ten pairs (2+1/4+3), spicules 54–64 μm long and fused for two-thirds of length, and gubernaculum 32–41 Μm long.

Relationships. The new species is morphometrically very close to the type and only species of the genus Distolabrellus , D. veechi (syn. D. pakistanensis ), as is shown in Table 2 . It differs significantly from the type population of D. veechi in its shorter female body length (0.89–1.07 mm vs 1.16–1.47 mm for D. veechi ), in the morphology of lips (three of them distinctly reduced, ovoid, lacking the conical inner ends and not extending to the entire thickness of cheilostom vs moderately developed, with conical inner ends and extending to the entire thickness of cheilostomal wall for D. veechi ), in the amphidial apertures being pore-like to oval (vs not clearly visible for D. veechi ), in having a shorter pharynx (126-162 μm vs 131-202 μm long for D. veechi ), in having the vulva located in a exceptionally large vulval cone (vs no elevated cone in D. veechi ), and in the rectum being shorter in females (30–40 μm vs 39–50 μm long for D. veechi ). D. magnivulvatus is distinguished from other populations of D. veechi by having the vulva a transverse slit (vs pore-like vulva in D. veechi ( Tahseen et al., 2009) , having no vulval plug (vs often having a plug of translucent material covering the vulva in D. veechi (Fig. IX in Doucet and Doucet, 1992, Fig.’s 2 & 3 in Carta et al., 2009)), and in the anterior lip of the vulva bearing a flap-like structure (vs no flap-like structure in D. veechi ).

Species Pharynx Tail V/Spicules Vulva to anus/ Country Reference

Gubernaculum

* Measurements from drawings or other measurements. ** Buccal tube.

Type habitat and locality. Soil of a greenhouse in Marchamalo (40°39'56.32"N, 3°11'49.77"W), province of Guadalajara, Spain. There was no plant culture at the time the nematodes were collected.

Type material. Female holotype, nine female and eight male paratypes deposited in the nematode collection of Departamento de Biología Animal, Biología Vegetal y Ecología, Universidad de Jaén, Spain. One female paratype and one male paratype deposited at USDANC, Beltsville, MD, USA. The rest of the paratypes were used for SEM. Etymology. The specific epithet is a Latin compound term meaning ‘large or huge vulva’ and refers to morphology of vulva region, so characteristic of the new species.

Remarks. Distolabrellus differs from other members of Mesorhabditinae Andrássy, 1976 in having dimorphic lips of two alternating shapes: this is an (aut)apormorphic condition vs the plesiomorphic state of all lips similar in morphology. The new species herein described displays two additional apomorphic conditions (three alternating lips reduced and presence of vulval cone) when compared with the type and only other species of the genus, and significantly widens the diversity of the genus.

We interpret the morphology of cuticle immediately anterior and posterior to the vulva not as a functional feature, caused by the protruded vulva, but as an anatomical feature associated with the vulval cone that characterizes and differentiates this species.

Figures

FIGURE 1. Distolabrellus magnivulvatus sp. n. A: Anterior region. B: Female genital branch. C: Female posterior region. D, E: Male posterior region (lateral and ventral views, respectively). F: Entire male. G: Entire female.

FIGURE 2. Distolabrellus magnivulvatus sp. n. (LM). A: Anterior region. B: Female posterior region. C: Body at vulva region level in lateral view showing the longitudinal fold of cuticle. D: Vulva (ventral view). E, F: Male posterior region at lateral view (at bursa and spicula levels, respectively). G: Male posterior region (ventral view). H: Lateral field.

FIGURE 3. Distolabrellus magnivulvatus sp. n. (SEM). A-C: Lip region (lateral, subdorsal and face views, respectively; amphids arrowed). D: Lateral field. E: Vulva. F, G: Female posterior region (ventral and lateroventral views, respectively). H: Male posterior region.

FIGURE 4. Schematic face view of lip region in Distolabrellus spp. A: D. veechi. B: D. magnivulvatus sp. n. Filled areas represent amphids.

Tables

TABLE 1. Morphometric data for Distolabrellus magnivulvatus sp. n. (measurements in Μm).

n 1	12	9
Body length 937	972.3 ± 54.3 (886–1074)	813.2 ± 87.4 (646–988)
a 26.0	24.1 ± 3.5 (18.7–29.2)	23.0 ± 2.4 (19.6–26.4)
b 5.3	5.4 ± 0.2 (5.1–5.9)	4.7 ± 0.4 (3.8–5.2)
c 12.0	12.2 ± 1.2 (10.9–14.6)	29.2 ± 3.1 (24.8–34.0)
c' 3.5	3.9 ± 0.6 (2.1–4.5)	1.2 ± 0.2 (1.0–1.4)
V 85	83.9 ± 1.1 (82–86)	-
Lip region: width 13	11.8 ± 1.1 (10–13)	11.4 ± 1.1 (10–13)
Stoma 28	26.7 ± 2.3 (22–30)	24.9 ± 1.8 (22–28)
Pharyngeal corpus 82	78.1 ± 3.6 (73–84)	71.0 ± 3.2 (64–74)
Isthmus 48	47.3 ± 4.3 (40–54)	43.8 ± 3.8 (38–48)
Basal bulb 28	28.5 ± 2.1 (25–32)	25.0 ± 1.5 (23–27)
Nerve ring-ant. end 124	129.9 ± 9.6 (114–145)	118.0 ± 10.8 (96–130)
Excretory pore-ant. end 159	151.5 ± 8.9 (139–168)	140.1 ± 13.8 (112–158)
Deirid-ant. end 173	161.5 ± 9.2 (155–168)	144.5 ± 13.4 (135–154)
Anterior to pharyngo-intestinal junction 177	180.3 ± 7.1 (168–190)	169.7 ± 8.1 (148–174)
Annuli width 1.5	1.8 ± 0.4 (1.2–2.5)	1.9 ± 0.4 (1.2–2.5)
Cuticle thickness 1.5	1.8 ± 0.4 (1.2–2.5)	1.7 ± 0.4 (1.2–2.5)
Body width: pharyngo-intestinal junction 30	33.7 ± 5.2 (27–47)	29.6 ± 2.9 (26–34)
midbody 36	41.0 ± 6.2 (34–56)	35.6 ± 3.3 (31–41)
vulva 36	37.8 ± 8.3 (22–56)	–
anus 22	21.0 ± 3.6 (18–32)	23.8 ± 1.8 (20–26)
Lateral field 2.5	3.0 ± 0.2 (3.0–3.5)	2.7 ± 0.3 (2.5–3.0)
Vagina 15	15.1 ± 2.2 (12–18)	-
Anterior ovary/testis 347	318.2 ± 54.1 (240–397)	222.3 ± 39.8 (154–306)
Anterior genital branch 302	439.8 ± 75.2 (302–572)	522.1 ± 60.5 (412–647)
Vulva-anterior end 794	815.6 ± 52.0 (737–908)	-
Vulva-anus distance 65	76.0 ± 10.4 (62–92)	-
Rectum 35	34.2 ± 3.1 (30–40)	12 (n=1)
Tail 78	80.0 ± 6.0 (68–90)	27.9 ± 3.0 (23–32)
Phasmid-anus distance 16	12.6 ± 2.1 (9–16)	?
Spicules -	-	61.0 ± 3.1 (54–64)
Gubernaculum -	-	37.3 ± 3.4 (32–41)

TABLE 2. Comparative morphometrics of Distolabrellus species.

Species Sex magnivulvatus sp. n. 13 Ƥ 9 33	L 0.89–1.07 0.65–0.99	a 18.7–29.2 19.6–26.4	b 5.1–5.9 3.8–5.2	c 10.9–14.6 24.8–34.0	c' 2.1–4.5 1.0–1.4	Stoma 22–30 22–28	Excretory pore 139–168 112–158
veechi 21 Ƥ 16 33	1.16–1.47 0.72–1.09	16.0–21.0 17.0–21.0	5.2–6.9 3.7–5.3	11.0–21.0 18.0–32.0	2.3–4.6 1.5–2.0	? 31*	161–202 131–184
40 Ƥ 40 33 as D. pakistanensis 21 Ƥ 15 33	0.96–1.23 0.76–1.06 1.33–1.86 0.89–1.24	11.9–22.1 15.7–23.5 14.0–17.2 17.0–20.0	4.6–6.8 4.1–5.5 6.9–8.4 5.8–6.8	13.2–19.8 28.6–39.2 17.0–20.0 35.6–39.6	2.3–4.4 0.9–1.3 2.5–3.0 0.8–1.1	22–25**? 30–32 24–27	140–185 137–171 175–200 170–180
29 Ƥ 28 33	0.89–1.78 0.67–1.33	15.0–24.0 17.0–26.0	4.1–7.6 3.9–6.3	10.5–15.0 22.4–34.8	2.5–5.1 1.1–1.6	26–47 21–35	??
13 Ƥ 7 33	0.92–1.24 0.75–1.10	16.0–24.0 18.0–23.0	4.8–5.9 4.0–5.6	12.5–16.6 26.1–36.6	3.1–4.2 1.1–1.4	28–35 24–30	??
continued.