Metoncholaimus perdisus, Russo & Pastor De Ward, 2019

Russo, Virginia Lo & Pastor De Ward, Catalina T., 2019, Three new species of the free-living marine nematode Metoncholaimus Filipjev 1918 (Enoplida, Oncholaimidae) from Argentinean coasts, Zootaxa 4688 (1), pp. 86-100 : 91-93

Metoncholaimus perdisus sp. n.

( Figure 3 ; Table 2 )

Measurements. See Table 2 .

Description. Males: Body cylindrical, slender, tapering towards the posterior end. Cuticle smooth. Lip region with six inner labial sensilla (R1) papilliform, 6 + 4 outer labial sensilla (R2) + cephalic sensilla (R3), 7–10 µm and 6–7 µm long respectively, arranged in a single circle just in the limit of endocupola. Buccal cavity with sclerotized walls, narrower in posterior part. Two subventral teeth and one dorsal tooth. Left subventral tooth is the longest (21 µm) and others are similar in length (ca 15 µm). Amphids opening oval (about 1/3 of the corresponding diameter) and fovea bowl-shaped. Some short cervical setae (3–5 µm) distributed anterior to nerve ring. Then, few longer somatic setae (ca 10 µm) scattered throughout body. Excretory pore faintly visible located in anterior part of pharynx at about two buccal cavity lengths from anterior end. Nerve ring lying at about 45% of pharynx length. Pharynx cylindrical. Cardia conoid, large. Diorchic reproductive system, with opposed and outstretched testes, in right position relative to intestine. Spicules paired, short, slender, not cephalate, ca 2 anal body diameter long. Gubernaculum small, delicate and tubular, 25% of the spicules length. Two pairs of precloacal setae and three pairs of postcloacal setae are present. Two tiny pre- and one postcloacal pore can be observed at cloaca. Tail ca 3 anal body diameters in length, conico-cylindrical in shape. Two pairs of short ventral and two dorsal (6 µm) caudal setae. Spinneret well developed with two short and two longer terminal seta. Dorsolateral and ventrolateral metanemes not observed.

Females: Similar to males in general body shape, anterior sensilla, amphideal fovea and cuticle. One anterior ovary, reflexed, on right side of intestine. Vulva slightly sclerotized, slit-like. Post-uterine sac present. Demanian system present ( Figure 5 ). Uterus connects through ductus uterinus with uvette (located ca 170 µm after vulva). Osmosium is located at ca 440 µm from vulva. Ductus entericus was not observed. The main tube starts at osmosium, ending at ca 170 µm into two terminal pores. Tail conico-cylindrical, but with cylindrical portion longer.

Type material. All the specimens are deposited in the CNP-NEM collection in the Centro Nacional Patagónico (Chubut, Argentina) .

Type locality and habitat. Holotype: adult male. Registration number CNP-NEM 16668; type locality: Banco Perdices (San Antonio bay); coordinates: 40°46ʹ52ʺ S; 64°51ʹ05ʺ W; low littoral, fine sand sediments. Collected by V. Lo Russo y G. Villares, 12 February 2009 . Paratypes: Four males and five females. Registration numbers CNP- NEM 16521/16727/16745/16798 (males) and CNP-NEM 16564/16711/16769/16827/19959 (females). Same data as holotype .

Etymology. In reference to “Banco Perdices”, the name of the site where the sample was collected.

Differential diagnosis. Metoncholaimus perdisus sp. n. is characterized by small size, short spicules, small gubernaculum, presence of long pre- and postcloacal setae and presence of pre- and postcloacal pores.

Metoncholaimus perdisus sp. n. belongs to the species of Metoncholaimus with short spicules (4 or less anal diameters in length) and presence of gubernaculum ( Table 4 ). Metoncholaimus perdisus sp. n. is thus related to M. amplus , M. anthophorus , M. moles , M. murphyi , M. pelor and M. siddiqii . M. amplus , M. pelor and M. siddiqii are bigger than the new species, have longer spicules, do not have somatic setae after the nerve ring (vs present in M. perdisus sp. n.) and just one precloacal pore (vs two pre- and one postcloacal pores in M. perdisus sp. n.) ( Table 4 ). M. amplus has spicules with cuticular ridges in the distal extremity unlike the new species that has spicules with smooth end. The females of M. amplus , M. pelor and M. siddiqii have slit-like pores in the Demanian system. M. perdisus sp. n. has rounded pores. M. anthophorus and M. moles have the excretory pore at the base of the buccal cavity vs two stomatal lengths from the anterior end in the new species. Also, they have many more cloacal setae ( Table 4 ). M. moles has a curved spicule (vs straight in M. perdisus sp. n.) and gubernaculum with apophysis (vs gubernaculum without apophysis). M. murphyi is similar to M. perdisus sp. n. in general body size and number of cloacal setae ( Table 4 ). The species can be differentiated by the presence of a bump in the males of M. murphyi , absent in the new species and in the length of the spicules. The Demanian system of females in M. murphyi has only one terminal pore vs two pores in M. perdisus sp. n. ( Table 4 ).

Figures

FIGURE 3. Metoncholaimus perdisus sp. n.: (A) Head region (internal) of holotype male (CNP-NEM 16668); (B) Head region (external) of holotype male (CNP-NEM 16668); (C) Posterior end of paratype female (CNP-NEM 16827); (D) Head region (in- ternal) of paratype female (CNP-NEM 16827); (E) Head region (external) of paratype female (CNP-NEM 16827); (F) Posterior end of holotype male in ventral view (sketch); (G) Posterior end of holotype male (CNP-NEM 16668). Scale bars: 1= 20 µm.

FIGURE 5. Reproductive and demanian system of paratype females: (A) Metoncholaimus sanmatiensis sp. n. (CNP-NEM 1655); (B) Metoncholaimus perdisus sp. n. (CNP-NEM 16959); (C) Metoncholaimus paracavatus sp. n. (CNP-NEM 1540). Scale bars: 1= 500 µm; 2= 200 µm; 3= 100 µm.

Tables

TABLE 2. Measurements (μm) of Metoncholaimus perdisus sp. n. including mean values (range).

	Holotype ♂	4 ♂	5 ♀
L	2620.0	2628 (2550–2720)	2470 (2220–2680)
a	68.9	72.3 (63.7–85)	58.7 (49.3–70.8)
b	6.6	6.6 (6.4–6.8)	5.9 (4.9–6.5)
c	35.4	34.8 (32.7–36)	21.4 (17.8–23.1)
Cephalic sensilla (R3)	6.0	6.4 (6–7)	5.6 (5–6)
Outer labial sensilla (R2)	7.0	8.6 (7–10)	7.8 (7–8)
Buccal cavity diameter	18.5	18.6 (14–24.5)	15.8 (12.5–18)
Buccal cavity length	30.0	30.6 (27–38)	26 (23–28)
Lip region diameter	28.0	24 (21–28)	27.3 (20–37)
Amphid diameter	9.0	8.94 (7–10)	7.6 (6–9)
Width of amphideal fovea as percentage of corresponding body diameter (%)	30.0	32 (23.3–42.2)	28.7 (20–38.1)
Cervical setae length	4.0	3.9 (3–5)	4.2 (3.5–5)
Excretory pore from anterior end	60.0	67.4 (60–76)	73.2 (61–93)
Nerve ring from anterior end	178.0	179.2 (170–188)	169 (153–175)
Body diameter at nerve ring	34.0	31.4 (28–36)	36.4 (30–39)
Pharynx length	400.0	397.6 (380–410)	416 (380–450)
Body diameter at pharynx base level	36.0	32.2 (28–38)	38.1 (29.5–43)
Maximum body diameter	38.0	36.6 (32–40)	42.4 (37–46)
Anal/cloacal distance from anterior end	2546.0	2552.4 (2472–2640)	2354.2 (2095–2564)
Anal/cloacal body diameter	28.0	26.2 (23–29)	28 (26–30)
Spicule length	51.0	50.4 (48–54)	–
Spicule length as cloacal diameter	1.8	1.9 (1.8–2.1)	–
Gubernaculum length	11.0	12.4 (11–13)	–
Gubernaculum length as cloacal diameter	0.1	0.07 (0.06–0.09)	–
Vulva from anterior end	–	–	1582 (1320–1730)
V (%)	–	–	64 (58.1–67.6)
Tail length	74.0	75.6 (71–80)	115.8 (100–125)
c’	2.6	2.9 (2.6–3.4)	4.1 (3.8–4.3)