Thoonchus covidus Zograf & Pavlyuk & Trebukhova & Baoquan 2020, sp. nov.
Creators: name: Zograf, Julia K.
name: Pavlyuk, Olga N.
name: Trebukhova, Yulia A.
name: Baoquan, Li
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Nematoda
Enoplea
Enoplida
Enchelidiidae
Thoonchus
Thoonchus covidus

description: Thoonchus covidus sp. nov.
(Figs 1–5; Table 1)
Diagnosis. Thoonchus covidus sp. nov. is characterized by the body length 3195–4339 µm, outer labial and cephalic setae in one circle, pocket shaped amphid above the buccal cavity base, secretory-excretory pore at the base of cephalic setae, arched spicules, gubernaculum with thin proximal extension parallel to spicules, preanal supplement absent, three pairs of preanal papillae.
Etymology. The species named after COVID-19 pandemic during which it was described.
Holotype. China: ♂, formalin-fixed, mounted on slide (MIMB 34000), in glycerin; deposited in the Zoological Museum NSCMB FEB RAS; collected in Sishili Bay (the Yellow Sea coast), 37 ° 27’32” N, 121 ° 29’29” E; sand, water depth 0.2–0.4 m. Collected by Yulia Trebukhova, June 27 th, 2018.
Paratypes. China: 1♂, 3♀♀, formalin-fixed, mounted on slides (MIMB 34001–34004), in glycerin; deposited in the Zoological Museum NSCMB FEB RAS; collected in Sishili Bay (the Yellow Sea coast), 37 ° 27’32” N, 121 ° 29’29” E; sand, water depth 0.2–0.4 m.
Type locality. China, Sishili Bay (the Yellow Sea coast), 37 ° 27’32” N, 121 ° 29’29” E; sand, water depth 0.2. 4 m.
Description. Body slender (Fig. 1A, D; 2A; 3A). Cuticle fine striated (Fig. 4C; 5D). Six short inner labial papillae (Fig. 4B). Outer labial and cephalic setae of equal length in one circle (Fig. 1B, E; 2B; 4 A–C; 5A). Cervical setae twice shorter than cephalic one; present from immediately posterior to amphid to level of nerve ring (Fig. 4A, C; 5 A–B). Somatic setae short, rare, irregularly scattered along the body. Caudal setae present (Fig. 4D; 5E). Buccal cavity large with heavily cuticularized walls and 3 teeth, right subventral tooth largest; size and position of left subventral and dorsal teeth about equal. About 5 complete irregular circles of small sharp denticles present anterior to dorsal and left subventral teeth (Fig. 1 B, E; 2 B–C; 3B; 4A–B). Amphids pocket shaped, slightly above the buccal cavity base (Fig. 1A, E; 3C; 4C; 5B). Secretory-excretory system present; ventral gland cell large, located at the level of anterior part of the intestine, extends anteriorly along the ventral side of the pharynx and opening to the exterior via pore at the base of cephalic setae (Fig. 1B, E). Pharynx long, muscular; not expanded at junction with intestine. Tail short. Spinneret and caudal glands present; caudal gland cell bodies not extend anterior to cloaca/anus.
Male. Length 3990–4339 µm, width at midbody 73–88 µm. Head diameter 49–53 µm at level of cephalic setae. Outer labial and cephalic setae 17 µm long (Fig. 1B; 2B; 4 A–C). Buccal cavity 35–44 µm long and 42–48 µm wide at level of denticles. Amphid 9.5–12.5 µm or 25% of corresponding body diameter wide (Fig. 4C). Pharynx 627–648.5 µm long; secretory-excretory pore 47–53 µm and nerve ring 235–272 µm from anterior end. Tail 99–104 µm or 1.5–2.24 anal body diameters long. As revealed with scanning electron microscope, there are three pairs of subventral papilla 20, 80 and 150 µm anterior to cloaca correspondingly (Fig. 4D). Two pairs of subventral setae immediately anterior to cloaca (Fig. 1C; 4D). Spicules 67.5–70.5 µm or 1.14–1.39 anal diameters long, arcuate (Fig. 1C; 2 D–E). Corpus of gubernaculum surrounding spicules; gubernaculum apophysis 53–55 µm long, parallel to spicules (Fig. 1C; 2 D–E).
Females. Length 3195–3975 µm, width at midbody 62.5–78.5 µm. Head diameter 39–45 µm at level of cephalic setae. Outer labial and cephalic setae 17.5 µm long (Fig. 1E; 5 A–B). Buccal cavity 37 µm long and 44 µm wide at level of denticles. Amphid 9–10 µm or 22.4% of corresponding body diameter wide (Fig. 3C; 5B). Pharynx 616–691 µm long, secretory-excretory pore 52 µm and nerve ring 241-303 µm from anterior end. Reproductive system amphidelphic with two opposed and reflexed ovaries. Vulva situated at ~1/2 of body length (Fig. 5C). Eggs large, elongated. One specimen characterized with the presence of gutter-shaped process extruded out of vulva (Fig. 3E). Two subventral rows of small rounded papillae 2 µm in diam. in pharyngo-genital region (Fig. 5E). Tail 83–99 µm or 1.74–2.26 anal body diameters long, with remarkable swelling in anal region (Fig. 3D; 5E).
Relationships. New species is closest to Thoonchus ferox in amphid size and position, in spicula and gubernaculum shape, and index a. Thoonchus covidus sp. nov. differs from T. ferox by body size (3195–4339 µm vs 2100–2200 µm), length of spicules (67.5–70.5 µm vs 32.4 µm) (Table 2), absence of precloacal supplementary organ, the number of pairs of precoacal papillae (tree pairs vs one pair) and presence of subventral rows of papillae in females. Thoonchus covidus sp. nov. differs from T. inermis by the bigger body size (3195–4339 µm vs 2153–2190 µm), longer spicules (67.5–70.5 µm vs 25–33 µm) and shape of gubernaculum (long dorsal apophysis vs short pointed apophysis). New species differs from T. longisetosus by the longer body (3195–4339 µm vs 2620 µm), longer cephalic setae (17 µm vs 8–12 µm), smaller amphids (9.5–12.5 µm vs 18 µm), longer spicules (67.5-70.6 µm vs 35 µm) and shape of gurbernaculum (long dorsal apophysis vs dorsocaudal apophysis). Described species differs from T. giganticus by the shorter body (3195–4339 µm vs 6500 µm) and tail (89–113 µm vs 205 µm), longer cephalic setae (17 µm vs 6.3 µm), shorter spicules (67.5–70.5 µm vs 558 µm), and shape of gubernaculum (long dorsal apophysis vs gubernaculums without apophysis) (Table 2).
description: Published as part of Zograf, Julia K., Pavlyuk, Olga N., Trebukhova, Yulia A. & Baoquan, Li, 2020, New species of Thoonchus (Enoplida, Enchelidiidae) from the Yellow Sea and redescription of T. giganticus Belogurova et al., 1986, pp. 239-252 in Zootaxa 4845 (2) on pages 241-247, DOI: 10.11646/zootaxa.4845.2.5, http://zenodo.org/record/4486679