Three new species of the free-living marine nematode Metoncholaimus Filipjev 1918 (Enoplida, Oncholaimidae) from Argentinean coasts Russo, Virginia Lo Pastor De Ward, Catalina T. Zootaxa 2019 2019-10-21 4688 1 86 100 Russo & Pastor De Ward, 2019 Russo & Pastor De Ward 2019 [151,463,1053,1080] Adenophorea Oncholaimidae Metoncholaimus Animalia Enoplida 5 91 Nematoda species perdisus sp. nov.  ( 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 µmand 6–7 µmlong 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 µmafter vulva). Osmosium is located at ca 440 µmfrom vulva. Ductus entericus was not observed. The main tube starts at osmosium, ending at ca 170 µminto two terminal pores. Tail conico-cylindrical, but with cylindrical portion longer.     Typematerial. Allthe specimens are deposited in the CNP-NEM collection in the Centro Nacional Patagónico( Chubut, Argentina).   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.  Type locality and habitat.  Holotype: adult male. Registrationnumber 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 Russoy 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  Metoncholaimuswith 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. pelorand  M. siddiqii.  M. amplus,  M. pelorand  M. siddiqiiare bigger than the new species, have longer spicules, do not have somatic setae after the nerve ring ( vspresent in  M. perdisus  sp. n.) and just one precloacal pore ( vstwo pre- and one postcloacal pores in  M. perdisus  sp. n.) ( Table 4).  M. amplushas spicules with cuticular ridges in the distal extremity unlike the new species that has spicules with smooth end. The females of  M. amplus,  M. pelorand  M. siddiqiihave slit-like pores in the Demanian system.  M. perdisus  sp. n.has rounded pores.  M. anthophorusand  M. moleshave the excretory pore at the base of the buccal cavity vstwo stomatal lengths from the anterior end in the new species. Also, they have many more cloacal setae ( Table 4).  M. moleshas a curved spicule ( vsstraight in  M. perdisus  sp. n.) and gubernaculum with apophysis ( vsgubernaculum without apophysis).  M. murphyiis 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. murphyihas only one terminal pore vstwo pores in  M. perdisus  sp. n.( Table 4). 2427924862 Argentina All Centro Nacional Patagonico 5 91 1 Chubut holotype 2427924863 2009-02-12 V. Lo Russo & G. Villares San Antonio bay -40.781113 Registration 19 -64.85139 Banco Perdices 7 93 1 holotype 2427924866 7 93 2 paratype