Metoncholaimus sanmatiensis, 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 : 88-91

Metoncholaimus sanmatiensis sp. n.

( Figure 2 ; Table 1 )

Measurements. See Table 1 .

Description. Males: Body cylindrical, slender, tapering towards anterior and posterior ends. Cuticle smooth. Lip region with six inner labial sensilla (R1) papilliform, 6 + 4 outer labial sensilla (R2) + cephalic sensilla (R3), 7–11 µm and 6–8 µm long respectively, in one circle at the end of the endocupola ( Belogurov & Belogurova 1989). Buccal cavity with sclerotized walls, twice as long as wide, 17–30 µm wide and 31–45 µm long. Two subventral teeth and one dorsal tooth (17 µm). Left subventral tooth is the longest (26 vs 22 µm for the right subventral tooth). Amphids opening ellipsoidal (about 1/3 of the corresponding diameter) and fovea bowl-shaped. The amphids are lo- cated at level with the middle part of the buccal cavity. Pharynx cylindrical, enlarged slightly posteriorly (1/9 times the body length). Scattered short cervical setae (ca 5 µm) in anterior part, posterior to amphids and anterior to nerve ring. Excretory duct opening through an ampulla in anterior part of pharynx at about two buccal cavity lengths from anterior end. Nerve ring lying at about 50% of the pharynx length. Cardia conoid, about one third of corresponding body diameter in length. Reproductive system diorchic, with opposed and outstretched testes, in right position relative to intestine. Spicules paired, slender, proximally slightly cephalate, 5.9–8.7 times anal body diameter long. Gubernaculum small, parallel to spicules, 10–15% of spicules length. Six pairs of precloacal setae and five pairs of postcloacal setae present. In addition, five tiny precloacal setae are distributed at regular intervals between cloaca and posterior part of spicule. Two tiny precloacal pores can be observed just anterior to cloaca. Tail ca 3.6 anal body diameter long, conoid, narrowing down posteriorly into a cylindroid part. About five short subdorsal setae are regularly spaced in caudal zone. In addition, two pairs of tiny setae at middle of tail. Spinneret well developed with two short terminal setae. Dorsolateral and ventrolateral metanemes not observed.

Females: Similar to males in general body shape, anterior sensilla, amphideal fovea and cuticle. One anterior ovary, reflexed, right to intestine. Vulva not sclerotized. Vagina directed anteriad. Demanian system present ( Figure 5 ). Uvette was not observed. Osmosium lies at ca 450 µm from vulva. Then the main tube divides into two short tubes (ca 360 µm) with moniliform glands, with terminal pore on each one. Tail conico-cylindrical in shape, with conical part representing about 2/3 of tail length.

Type material. Holotype and some paratypes are deposited in the CNP-NEM collection in the Centro Nacional Patagónico (Chubut, Argentina). One paratype is deposited in the National Collection of Invertebrates of the Museo Nacional de Ciencias Naturales ‘ Bernardino Rivadavia’ ( Argentina).

Type locality and habitat. Holotype: adult male. Registration number CNP-NEM 1645; type locality: San Antonio Oeste; coordinates: 40°43ʹ 66ʺ S; 64°58ʹ19ʺ W; low littoral, fine sand sediments. Collected by C. Pastor, 5 March 2006. Paratypes: Nine males and nine females. Registration numbers MACN-In 38923 (male), CNP-NEM 1646–1653 (males) and CNP-NEM 1654–1662 (females). Same data as holotype.

Etymology. In reference to the name of San Matías gulf, where the sample was collected.

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

The new species is closely related to M. albidus , M. amplus , M. longiovum and M. uvifer by the similar length and shape of spicules, similar configuration of cloacal setae ( Table 4 ) and general body shape. M. sanmatiensis sp. n. has gubernaculum whereas M. albidus does not have a real one, only a thickening in the distal part of the spicule ( de Man 1893). The new species has two pores in the cloacal region which are not present in M. albidus , whereas the latter species has a prominent cloacal bulge. The females of both species can be differentiated by the number of Demanian pores (1 in M. albidus vs 2 in M. sanmatiensis sp. n.) ( Table 4 ) and the presence of a cuticularised girdle in M. albidus . M. amplus males have only one precloacal pore and a shorter spicules with cuticular ridges in the distal extremity. The females of this species have slit-like pores in the Demanian system, and these pores lie approximately one-third the distance between vulva and anus. M. sanmatiensis sp. n. has rounded pores, and they are approximately half-way between vulva and anus. M. longiovum and M. uvifer both have higher number of postcloacal setae (19 and 10–14 respectively) than M. sanmatiensis sp. n. (5) and do not have cloacal pores ( Table 4 ). M. longiovum has the excretory pore more than two stomatal lengths from the anterior end vs ca two in the new species.

Figures

FIGURE 2. Metoncholaimus sanmatiensis sp. n.: (A) Head region (internal) of holotype male (CNP-NEM 1645); (B) Head region (external) of holotype male (CNP-NEM 1645); (C) Posterior end of paratype female (CNP-NEM 1654); (D) Head region (internal) of paratype female (CNP-NEM 1654); (E) Head region (external) of paratype female (CNP-NEM 1654); (F) Posterior end of holotype male showing the entire spicule (CNP-NEM 1645); (G) Posterior end of holotype male with detail of the cloacal region (CNP-NEM 1645). Scale bars: 1= 20 µm; 2= 200 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 1. Measurements (μm) of Metoncholaimus sanmatiensis sp. n. including mean values (range).

	Holotype ♂	9 ♂	9 ♀
L	4920.0	4706.5 (4175–5375)	5180 (4630–5740)
a	48.2	47.1 (38.6–56.9)	44.3 (37–52)
b	9.3	8.9 (7.3–10.1)	9.2 (8.5–10.3)
c	42.4	40.2 (33.9–49.3)	38.2 (31.6–61.8)
Cephalic sensilla (R3)	6.0	7.3 (6–8)	7.9 (7–9)
Outer labial sensilla (R2)	7.0	9 (7–11)	9.6 (9–10)
Buccal cavity diameter	17.0	21.3 (17–30)	21.3 (18–29)
Buccal cavity length	33.0	36.9 (31–45)	38.4 (36–42)
Lip region diameter	30.0	33.2 (28–41)	34.6 (31–41)
Amphid width	9.0	9.4 (7–12)	10.7 (9–13)
Body diameter at amphid level	31.0	34.9 (30–46.5)	37.1 (34–47)
Width of amphideal fovea as percentage of corresponding body diameter (%)	29.0	27.1 (21.2–30.9)	28.8 (25.7–32.4)
Excretory pore from anterior end	65.0	82.6 (65–96)	79.6 (66–103)
Nerve ring from anterior end	270.0	263 (230–290)	285.6 (245–340)
Body diameter at nerve ring	77.0	73.9 (60–90)	79.1 (69–89)
Pharynx length	530.0	530.5 (470–590)	562.8 (510–640)
Body diameter at pharynx base level	100.0	91.3 (73–112)	104.6 (87–115)
Maximum body diameter	102.0	101.2 (81–129)	117.7 (104–138)
Anal/cloacal distance from anterior end	4804.0	4588.5 (4052–5264)	5039.9 (4490–5580)
Anal/cloacal body diameter	30.0	33 (29–39)	43.9 (38–51)
Spicule length	260.0	238.2 (210–260)	–
Spicule length as cloacal diameter	8.7	7.3 (5.9–8.7)	–
Gubernaculum length	30.0	30.1 (25–36)	–
Gubernaculum length as cloacal diameter	1.0	0.9 (0.8–1.1)	–
Vulva from anterior end	–	–	3176.1 (2885–3460)
V (%)	–	–	61.4 (58.4–67.8)
Tail length	116.0	118 (96–135)	140.1 (85–160)
c’	3.9	3.6 (2.5–4)	3.2 (2–3.8)