Thoonchus giganticus Belogurova et al., 1986

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, Zootaxa 4845 (2), pp. 239-252 : 248-249

Thoonchus giganticus Belogurova et al., 1986

( Fig 6 , Table 1)

Redescription. Body fusiform, narrowing to the head end, 6905 µm long. Width at midbody 362 µm. Head end blunt. Inner and outer labial sensilla indistinct. Cephalic setae 9 µm long. Amphids pocket-shaped, situated at the base of the buccal cavity. Buccal cavity small, 31 µm deep. Three unequal teeth in the buccal cavity. The biggest right subventral tooth 25 µm long ( Fig. 6B ). About 5 complete irregular circles of small sharp denticles present. Pharynx long, muscular, 1566 µm long. Secretory-excretory system not visible. Spicules curved, cephalated, 553 µm or ca 5 cloacal diameters long ( Fig. 6D ). Gebernaculum stick-shaped, without apophysis. Supplements absent. A ventral row of 7 papilla anterior to cloaca ( Fig. 6E ). Two ventral setae immediately anterior to cloaca. Tail conicocilindrical, 246 µm or 2.3 cloacal diameters long ( Fig. 6C ).

Remarks. Belogurova and co-authors (1986) described Thoonchus giganticus from the Tatar Strait ( Fig. 7 ). Authors placed this species among Thoonchus based on the presence of three teeth and small denticles in the buccal cavity and the absence of supplements in male. Later on, Keppner (1988) mentioned that the shape of buccal cavity, teeth, and male genital apparatus deviate significantly from that of Thoonchus . He also noted that this species is difficult to place within existing genera of Enchelidiidae or erect a new genus for it. Therefore, Thoonchus giganticus might be considered of doubtful generic assignment ( Keppner, 1988). We agree that T. giganticus deviates greatly from other Thoonchus species, but we propose considering it incertae sedis till the new genus is established.

Figures

FIGURE 6. Male of Thoonchus giganticus Belogurova et al., 1986. Light microscopy (DIC). A. General view. B. Right subventral tooth. C. Tail. D. Spicules. E. Precloacal papillae.Abbreviaton: p—papillae. Scale bars: A—200 µm; B—10 µm; C—50 µm; D—100 µm; E—20 µm.

FIGURE 7. Map of distribution of species of the genus Thoonchus. 1—T. ferox, 2—T. inermis, 3—T. giganticus, 4—T. longisetosus, 5—T. covidus sp. nov.