Metadesmolaimus innii Fadeeva & Karpova 2024
Creators: name: Fadeeva, Natalia P.
name: Karpova, Alena A.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Chromadorea
Monhysterida
Xyalidae
Metadesmolaimus
Metadesmolaimus innii

description: Metadesmolaimus innii sp. nov.
(Figures 2–3, Table 1)
Type material. Holotype adult male (MN 261020) and four paratypes males (MN 240723) and six paratypes females (MN 261020; MN 190821), 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 261020) was collected from intertidal fine sandy sediments, 0.4 m depth, Russia, the Vostok Bay of the Japan Sea on 26 October 2020. Four paratypes males (MN 240723), as well as five paratypes females (MN 261020) were collected from sandy sediments from 0.4 to 0.5 m depth, 26 October 2020 and 24 July 2023.
Additional locality. One paratype female (MN 190821) intertidal fine sandy sediment from 0.4 m deep, Triozerye Bay, the Japan Sea, 19 August 2021.
Etymology. The species epithet is named in honour of Senior Researcher Inna V. Stonik of A.V. Zhirmunsky National Scientific Centre of Marine Biology, Russia.
Descriptions
Males. Spindle-shaped plump brownish nematodes with distinctly annulated cuticle (2 µm). Six internally striated lips and six inner labial setae (2–3 µm long). Six outer labial setae (0.7 hbd—corresponding head body diameter) and four cephalic setae (1–1.2 hbd) and occasionally a third setae of intermediate length (6 µm) may be distinguished in the submedian groups (Figure 3A; Table 1). Setae in these submedian groups are usually difficult to distinguish as they are closely applied to one another. Numerous somatic setae in the cervical (13–14 µm long), in the middle (9–10 µm long) and caudal regions (15 µm long).
Buccal cavity unarmed, extended, divided into anterior high cheilostom (3–4 µm depth) and posterior conical esophastom (6–9 µm depth) by a distinct stomatoidal cuticular ring (Figures 2B, 3A). Pharynx cylindrical for most of its length, muscular, gradually widening to the base with developed cardia. Nerve ring difficult to distinguish.
Amphideal fovea conspicuous, elliptical, 0.7–0.8 hbd, 0.9–1 hbd from anterior end. Two pairs of setae, about 7–8 µm long, situated at the posterior edge of amphideal fovea. Renette cell body and excretory pore indistinct.
Tail conical, 104–118 µm long (4 cloacal body diameter, cbd), gradually tapering toward the distal end, similar in shape in both sexes. No terminal setae (Figures 2A, 2C, 3B, 3C; Table 1).
Reproductive system diorchic with two opposed testes, the anterior testis is to the left of the intestine, the posterior one is to the right. Spicules thin, unequal in length, the right one (4–5 cloacal body diameter) is notably longer and slightly curved, without cephalated proximal end; left spicule shorter (2–3 cloacal body diameter) (Figure 3B). Gubernaculum tubular (18–20 µm long), surrounding distal end of each spicule, with dilated, serrated distal edge, apophysis absent.
Females. Similar to males in general characteristics (Figures 2D, 3D, 3E, 3F). Amphideal fovea circular relatively smaller (0.5–0.6 hbd) and more posterior from anterior end (1.8 hbd) (Figure 2E). There are no cervical setae at this level. Reproductive system monodelphic, ovary outstretched, located left of the intestine in the anterior half, to the right of the intestine in the posterior half (Figure 3H). Tail conical, 76–117 µm long (3 cbd) (Figure 3G, Table 1).
Diagnosis. M. innii sp. nov. is characterized by the combination of the brownish cuticle colour, sexual dimorphism in the shape of the amphideal fovea (elliptical in males, circular in females), unequal long spicules. Buccal cavity extended, divided by a distinct stomodeal cuticular ring into anterior domed cheilostom and posterior conical esophastom.
Differential diagnosis. The new species belongs to the group of species M. caniculus Wieser & Hopper, 1967 and M. varians Lorenzen, 1972; characterized by the moderate length of the body, cuticle with clear annulations, very long and thin spicules (more than two cloacal body diameters). M. innii sp.nov. differs from them with the asymmetry and shape of spicules (in all cases, the right spicule is longer than the left one). The new species can be separated from M. caniculus by the shorter body (802 µm vs 1600 µm), and shape of spicules and size (110–158 µm vs 135 µm). M. varians differs from the new species in size of spicules (56–79 µm vs 110–158 µm) and tail shape (elongated cylindrical with terminal setae vs conical without setae).
description: Published as part of Fadeeva, Natalia P. & Karpova, Alena A., 2024, New species of Metadesmolaimus, Rhynchonema and Gairleanema (Nematoda) from the sandy beaches of the Sea of Japan, pp. 115-132 in Zootaxa 5537 (1) on pages 117-121, DOI: 10.11646/zootaxa.5537.1.6, http://zenodo.org/record/14239338