Free-living marine nematodes of the genus Richtersia Steiner, 1916 (Desmodorida: Richtersiidae) from the Sea of Japan Author Revkova, Tatiana N. 0000-0002-3500-3776 A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS, 2, Nakhimov ave., 299011, Sevastopol, Russia alinka8314@gmail.com Author Sergeeva, Nelli G. 0000-0002-3984-0918 A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS, 2, Nakhimov ave., 299011, Sevastopol, Russia nserg05@mail.ru text Zootaxa 2024 2024-12-02 5543 1 123 134 https://doi.org/10.11646/zootaxa.5543.1.7 journal article 10.11646/zootaxa.5543.1.7 8b3d0c0b-ae3b-4f61-b9da-84106746b7ce 1175-5326 14385317 093A5AA0-DAEF-4312-B8D9-897F7A6B779C Richtersia amurica sp. nov. ( Figures 4–5 , Table 1 ) Type material. Six males and six females . Holotype male mounted on slide Meib.53.N.h. , five paratype males mounted on slides: Meib.19.N.p. ( 2 males ), Meib.55.N.p. , Meib.57.N.p. , Meib.58.N.p. and six paratype females: Meib.22.N.p. , Meib.23.N.p. , Meib.25.N.p. , Meib.51.N.p. , Meib.52.N.p. , Meib.54.N.p. in pure glycerin . Type locality and habitat. Amur Bay , Sea of Japan , 20 June 2021 , station 11, water depth 6 m , dense silt, finegrained sand, coordinates: N 42°52.471 , E 131°39.202 . Etymology. The new species epithet “ amurica ” refers to the locality of collection, the Amur Bay. Descriptions. Males. Body plump, short, truncated anteriorly and tapering posteriorly. Cuticle annulated about 1 μm in width. Each annule carrying backward-pointing spines about 36–38 rows in the anterior part, 22–24 rows in the mid-body region and 13–15 rows in the cloacal region. Posterior half of the tail lacking spines but with irregular annules; the tail tip is smooth. On the ventral side, longitudinal rows of robust spines located approximately 19–24 µm from the cloaca. Somatic setae 5–6 μm long in eight rows. The six internal labial setae 9–11 μm long, situated on a hyaline labial membrane; the six external labial setae 8–9 μm long and four cephalic setae 4–5 μm long, at almost the same level. Subcephalic setae 5–6 μm long, one at each side of amphidial fovea. Amphidial fovea large with 3.5 turns, surrounded by spines, 46.9–59.7% of chd . Stoma large, unarmed and partly surrounded by pharyngeal tissue. Pharynx cylindrical lacking a posterior bulb. Cardia triangular, surrounded by the intestine. The intestinal cells containing dark brown granules, more abundant in the anterior part of the intestine. Nerve ring and secretory-excretory system unclear. Reproductive system monorchic, with outstretched testis, lying partially ventral to the intestine. Two spicules unequal in shape and size: the right spicule very fine 2.8 (3.4–4.6 times cloacal body diameter) and the left spicule wide 1.0 (0.9–2.0 times cloacal body diameter) with a capitulum; right spicule 2.0–2.7 times longer than the left spicule. Gubernaculum surrounding distal ends of spicules. Tail short, 1.1 (1.1–1.7) cbd long. Three caudal glands present. FIGURE 4. Richtersia amurica sp. nov. A: holotype male, entire body; B: holotype male, amphidial fovea; C: paratype female, amphidial fovea; D: holotype male, spicules; E: paratype female, entire body; F: holotype male, head; G: paratype female, head. Scale bar: A, E = 100 μm; B–D, F, G = 20 μm. FIGURE 5. Richtersia amurica sp. nov. A: holotype male, entire body; B: holotype male, head region; C: paratype female, head region; D: holotype male, tail region; E: holotype male, amphidial fovea; F: paratype female, amphidial fovea; G: paratype female, tail region (Meib.25.N.p.); H: paratype female, vulva; I: paratype female, entire body; J: paratype female, cuticule on vulval region. Scale bar: A, I = 100 μm; B–H, J = 20 μm. Female. General morphology similar to that of male. Amphidial fovea smaller, 23.5–29.4 % of chd, with one turn. Cardia invisible. The intestine is abundantly filled with dark brown granules in the anterior part. Reproductive system didelphic, amphidelphic. Ovaries reflexed. The tail is covered with long hairy spines ( Figure 5G ), longer on the dorsal side than those on the ventral side. Diagnosis. Richtersia amurica sp. nov. is characterised by the number of longitudinal spines rows, located at the level of amphidial fovea; amphidial fovea with 3.5 turns in males and one turn in females; spicules unequal, gubernaculum with anterior apophyses in males; tail conical and short; females tail with long hairy spines. Differential diagnosis. Richtersia amurica sp. nov. is similar to R. inaequalis , R. coomansi , R. beibuwanensis and R. staresensis in having unequal spicules and in amphidial fovea structure in males and females. However, R. amurica sp. nov. differs from them by the length of left (53–69 μm vs . 39–47 μm in R. inaequalis , 124–185 μm in R. coomansi , 98.2–108 μm in R. beibuwanensis , 41–46 μm in R. staresensis ) and right (123–144 μm vs . 113–126 μm in R. inaequalis , 66–85 μm in R. coomansi , 44–50.9 μm in R. beibuwanensis , 87–93 μm in R. staresensis ) spicules. In the arrangement of longitudinal spine rows beginning at the level of the amphidial fovea and in long hairy spines on the tail of females, the new species resembles R. inaequalis and R. coomansi , but it differs from them by the presence of anterior apophyses on gubernaculum ( vs . absent). R. amurica sp. nov. also differs from R. inaequalis by having a relatively broader body (a = 8.9–10.7 vs . 12–14.4 in males and 6.6–9.4 vs. 10.5 in females) and longer internal labial setae (9–11 μm vs . 6.3–7 μm). The new species can be distinguished also from R. coomansi by the spirally whorled amphidial fovea in males (3.5 turns vs . 5.25 turns) and internal labial setae without a prominent base ( vs . present). The new species is similar to R. beibuwanensis and R. staresensis by the presence of anterior apophyses on the gubernaculums, but differs from them by patterns of longitudinal spine rows (at the level of amphidial fovea vs . middle of the pharynx). R. amurica sp. nov. also differs from R. beibuwanensis by having a longer body (515–895 μm vs . 373.7–405.6 μm), longer internal and external labial setae (9–11 μm and 8–9 μm vs . 6 μm), higher index c (10.5–24.2 vs . 6.6–7.5) and shorter amphidial fovea in females (23.5–29.4% vs . 36.3%). Furthermore, the new species differs from R. staresensis by having a smaller amphidial fovea in males (46.9–59.7% chd with 3.5 turns vs . 90% chd with 4 turns).