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

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Metoncholaimus perdisus

sp. n.

Metoncholaimus perdisus sp. n.

( Figure 3 View FIGURE 3 ; Table 2 View TABLE 2 )

Measurements. See Table 2 View 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 View 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 GoogleMaps . Paratypes: Four males and five females. Registration numbers CNP- NEM 16521 View Materials /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 View 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 View 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 View 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 View 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 View TABLE 4 ).

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)