Gairleanema arenosa, Fadeeva & Karpova, 2024

Fadeeva, Natalia P. & Karpova, Alena A., 2024, New species of Metadesmolaimus, Rhynchonema and Gairleanema (Nematoda) from the sandy beaches of the Sea of Japan, Zootaxa 5537 (1), pp. 115-132 : 126-130

Gairleanema arenosa sp. nov.

( Figures 6–8 , Table 2)

Type material. Holotype adult male ( MN 210821-1 ) and five paratypes males ( MN 210821-5 , MN 230883 ), and three paratypes females ( MN 210821-3 , MN 230883 ); formalin-fixed, mounted on slides, in glycerin, deposited in the nematode collections of the Division of Biological Sciences , Zoological Museum of Far Eastern Federal University, Vladivostok, Russia.

Type locality. Holotype ( MN 210821-1 ) was collected from intertidal fine sandy sediments, 0.5 m depth in Vostok Bay ; Primorsky Krai , Sea of Japan, 21 August 2021. Four paratypes males ( MN 210821-5 ,) and two paratypes females ( MN 210821-3 ) were collected from intertidal fine sandy sediments, 0.5 m depth in Vostok Bay, Sea of Japan, 21 August 2021.

Additional locality. One paratype male, as well as one paratype female ( MN 230883 ) were collected in sandy sediment from 2 m depth, Primorsky Krai , Kievka Bay, Sea of Japan, 23 August 1983 .

Etymology. The species epithet is an adjective derived from the type locality, from the Latin word “ arenosa ” (sand).

Descriptions

Males. Body cylindrical, weakly tapering toward both ends. Head rounded at the anterior end ( Figures 6A, 6D , 7A, 7D , 8A ). Mouth opening wide, surrounded by three thin deeply incised lips. Cuticle with yellow color, 2 µm thick, fine transverse striations with numerous small dots. The cephalic capsule without distinct anterior lobes, and with weakly expressed posterior lobes ornamented by numerous larger dots than in other parts of the body. Its walls are thinner at the anterior end than at the posterior end.

Six setiform inner labial sensillae with bulbous swellings, acute at distal end, six very long (1.2 hbd long) setiform outer labial sensillae; four small and thin cephalic setae (0.3–0.4 hbd long). Somatic setae absent. Amphideal fovea comprise 30% hbd located at the posterior edge of the capsule, ( Figure 8B ) unispiral with circular aperture, inner margin more distinct than outer; 0.9 hbd from anterior body end.

Buccal cavity with a pointed, heavily sclerotized dorsal tooth which enters between two triangular subventral onchia. A pair of small denticles situated on both sides of the subventral onchia. Pharynx cylindrical, surrounding buccal cavity and thickened in the dorsal and subventral sectors. Cardia short, surrounded by intestine. Excretory pore not visible. Nerve ring situated at 35–40% of pharynx length from anterior. The tail consists of conical and cylindrical parts, pore subterminal.

Reproductive system monorchic with anterior outstretched very long testis (800 µm). Spicules slender with large capitulum (2 x 3). Spicules curved are almost at right angles, 1.3–1.4 abd long, gubernaculum paired with hooked dorsal apophyses ( Figure 6E ). Developed paraterminal, caudal and precloacal setae. Four–five pairs of mamilliform supplementary organs inserted in the precloacal cuticle ( Figures 6E , 7G, 7H ). Supplementary organs present an intracuticular canal on the surface of the cuticle ( Figures 7G, 7H ). Presence of a 14 µm long ventral precloacal setae. The distances from the cloaca to the anterior pair of supplements are 65–80 µm, to the posterior are 23–27 µm. Postcloacal subventral setae 5–6 µm long; two terminal setae 12–14 µm long. Tail elongated, 5–6 cbd long, relatively slender, with terminal spinnerete tube ( Table 2).

Females. Similar to male in general characteristics ( Figures 6B, 6C , 7B, 7C, 7I ). Reproductive system ( Figure 7F ) didelphic, with opposed, reflexed ovaries on right side of intestine. Vulva slit-like, located at 52–65% of body length. Vagina weakly sclerotized. Females have setae at the level of the end of the esophagus and in the vulva area, but paraterminal and caudal setae are absent. Presence of paravulvar setae with 14 µm length.

Diagnosis. Gairleanema arenosa sp. nov. is characterized the combination of the following characters: moderately long body (1445–1707µm), long setiform labial sensilla with presence of bulbous swellings and thin cephalic setae; unispiral small amphideal fovea located at the posterior edge of the cephalic capsule, dorsal tooth, two subventral onchia and small denticles; four–five pairs mamilliform supplementary organs.

Differential diagnosis. The new species differs from the other known Gairleanema species by the presence of 4–5 pairs of precloacal mamilliform supplements on the caudal region of males.

The new species Gairleanema arenosa sp. nov. differs significantly from G. anagremilae Warwick & Platt, 1973 in having one dorsal tooth and two subventral onchia with small denticles vs one dorsal tooth and two subventral onchia (without denticles); the length of spicules (32–39 μm vs 52–53 μm).

The new species also differs from G. pulchra Liang, Guo & Wang, 2024 with the combination of characters of buccal cavity (dorsal tooth, two subventral onchia and small denticles); the length of the outer labial setae (42–45 μm in G. arenosa sp. nov. vs 46–59 μm in G. pulchra ), unispiral small amphideal fovea and the position of the amphidial fovea from the anterior end (21–23 μm vs 27–29 μm); shorter tail (135–145 μm vs 149 μm and “c” 11–13 vs 10).

Additional Remarks. Nematodes of the genus Gairleanema rarely occur in samples of marine sediments. Until recently the species composition of the genus remained unchanged. Nematodes of the genus were registered in different regions: Kawi, Sabah, Malaysia (Indian Ocean) ( Long & Ross 1999; Liang et al. 2024), and Russian coast, the Sea of Japan, rather far from their respective type locality (Firemore beach, Scotland).

Figures

FIGURE 6. Gairleanema arenosa sp. nov.. Male holotype. A: Head region; D; Entire body; E: copulatory apparatus. Female paratype. B: Head region; C: Entire body; F: Lateral view of tail region; (Scale bars: C, D—100 μm, A, B, E, F—20 μm).

FIGURE 7. Gairleanema arenosa sp. nov.. Micrographs of paratypes. Male. A: Entire body; D: Head region; E: Copulatory apparatus; G: Supplements; H: Lateral view of tail region. Female. B: Entire body; C: Head region; F: Vulva; I: Lateral view of tail region; (Scale bars: A, B—100 μm; C, D, E, G, H—20 μm, F, I—50 μm).

FIGURE 8. Gairleanema arenosa sp. nov.. A, B: Laser-scanning microscopy pictures. A: Lateral view of male head; B: detail of female head; (Scale bars: A, B—25 µm).