Aponema pontica, Revkova, 2017

Revkova, Tatiana N., 2017, Two new species of free-living nematodes genera Microlaimus de Man, 1880 and Aponema Jensen, 1978 (Nematoda: Microlaimidae) from the Black Sea, Zootaxa 4344 (2), pp. 387-394 : 388-389

Aponema pontica sp. n.

Figure 1 , Table 1

Material examined: five males, four females. Glycerin-gelatin slides. Holotype: male on slide # FlN/BS–1. Paratypes: males, from FlN/BS–2 to FlN/BS–5; females, from FlN/BS–6 to FlN/BS–9.

Type locality: Black Sea, Crimea shelf, oxic/anoxic interface at the region of submarine Dnieper Canyon. Depth 120 m, (1–2 cm horizontal layer), sandy silt and 170 m (0–1 cm), silt; Sevastopolskaya Bay, depths 14–17 m, silt.

Etymology. The species name is derived from the Greek Pontos = Black Sea.

Description. Male Body spindle-shaped, slender. Cuticle transversely striated. Striation beginning immediately posterior to cephalic setae. Somatic setae 3 µm long, scattered along the body. Inner and outer labial sensillae inconspicuous; four cephalic setae, 4 µm long. Head not separated from the remaining body. Cryptocircular amphidial fovea with interruption in the posterior part, located 5–8.5 µm from anterior edge. Buccal cavity small, with one dorsal and two ventrosublateral teeth. Pharynx cylindrical with well-developed terminal rounded bulb, 26 µm in width. Intestine filled with rounded, slightly yellow-brown inclusions. Anterior part of intestine with annular structure. Nerve ring is located at the level of middle of pharynx. Secretory-excretory system present; renette lies ventrally to the posterior part of pharyngeal bulb, cardia and anterior part of the intestine. Secretory-excretory pore located between the nerve ring and the bulb, posterior to nerve ring. Cardia small and triangular.

Reproductive system monorchic, single anterior outstretched testis situated to the right of intestine. Spicules arcuate, distally tapering. Gubernaculum with dorso-caudally directed apophyses; dorso-caudal part 5–7 µm long, 5–6 µm wide and dorsally curved part 5–6 µm long. Apophyses are more strongly sclerotized along dorsal margin. Tail conico-cylindrical, elongated, with slightly swollen tip. Somatic setae on tail 3–4 µm long. Three caudal glands presence. Spinneret present.

Female Similar to male in most parameters. Reproductive system didelphic, posterior and anterior ovaries of equal length, outstretched. Both ovaries located to the right of intestine. Vulval lips not sclerotized, slightly protruding beyond body contour and situated at 40% from the anterior end. Vagina short, with thin walls. Uteri large, contain large oocytes, 44 µm long. No vulvar glands seen.

Diagnosis. Aponema pontica sp. n. is characterized by slender (611–966 µm) body. Cuticle transversely striated. Head not separated from the remaining body. Amphidial fovea cryptocircular with interruption in the posterior part. Oesophagus narrow, posteriorly forming a rounded and weakly sclerotised lumen of pharyngeal bulb. Female reproductive system didelphic, ovaries outstretched; male reproductive system monorchic. Tail conico-cylindrical, elongated, with slightly swollen tip. Short setae in the pre- and post-cloacal regions present.

Discussion. Aponema pontica sp. n. differs from all known Aponema species by the absence of the constriction in head region and in the shape of gubernacular apophyses. New species is morphologically closest to A. torosum (Lorenzen 1973) Jensen 1978 and A. subtile Leduc & Wharton 2008 . A. pontica sp. n. is similar to A. torosum in the shape of the body, size of amphids, the value of ‘b’ and ‘c’, but differs in having small and triangular cardia, rounded and weakly sclerotised lumen of pharyngeal bulb and longer spicules (35–43 µm vs 28–37 µm in A. torosum ). A. pontica sp. n. is similar to A. subtile in the shape and length of the body, structure of pharyngeal region and presence of short setae in the pre- and post-cloacal regions, but can be differentiated from A. subtile in the shape and length of spicules (35–43 µm vs 22–27 µm in A. subtile ), low values: ‘a’ (13.3–21.6 vs 30.8–39.4 in A. subtile ), ‘b’ (6.4–7.8 vs 7.8–8.8 in A. subtile ), ‘c’ (5.1–6.3 vs 6.7–8.4 in A. subtile ), tail setae longer (3–4 vs 1–2 µm in A. subtile ) and size of the amphidial fovea (5.0–5.5 (43.5–53.0%) vs 3–4 (31–40%) in A. subtile ).

Figures

FIGURE 1. Aponema pontica sp. n. Holotype male and paratype female. A: male, head; В: female, head; С: male, pharyngeal region; D: male, total view; E: female, total view; tail; F: female, pharyngeal region; G: female, tail; H: male, copulatory apparatus; I: male, tail. Scale bars: A, B = 10 µ m; H = 20; C, F, G, I = 50 µ m; D, E = 100 µ m.