Linhomoeus pycnocricus sp. nov. urn:lsid:zoobank.org:act: 7E20B27F-A479-47FF-8BCF-A0640FC9656D Figs 4–6, Table 3 Diagnosis Linhomoeus pycnocricus sp. nov. is characterized by body length 3.8–5.6 mm, ratio of a = 40–50, 6 + 16 arrangement of cephalic sensilla with six outer labial setae 5–6 µm or 17–25% cbd long, four slightly shorter cephalic setae 3–4 µm or 10–16% cbd long, and six additional setae similar in length to outer labial setae; eight subcephalic setae present, 4–6 µm long; strongly cuticularized amphidial fovea 35– 40% cbd wide; buccal cavity cup-shaped with strongly cuticularized base and walls; secretory-excretory pore located at level of nerve ring or immediately posterior or anterior; spicules 0.9–1.1 cloacal body diameters long, gubernaculum with straight dorsocaudal apophyses, 25–27 papilliform precloacal supplements present; conicocylindrical tail, 5.5–9.8 cloacal/anal body diameters long. Differential diagnosis The new species is most similar to L. anteporus (Vitiello, 1969) Fonseca & Bezerra, 2014, L. bocki (Schuurmans Stekhoven, 1946) Fonseca & Bezerra, 2014, L. brevisetosus Schuurmans Stekhoven, 1946, L. caxinus (Vitiello, 1969) Fonseca & Bezerra, 2014, L. conicaudatus (Allgén, 1930) Fonseca & Bezerra, 2014, L. deconincki (Groza-Rojancovski, 1972) Fonseca & Bezerra, 2014, L. ordinarius (Wieser, 1956) Fonseca & Bezerra, 2014, and L. undulatus Wieser, 1959, 2014, and in having relatively short cephalic setae and outer labial setae (<40% cbd). Linhomoeus pycnocricus sp. nov. differs from L. anteporus in longer body length (3.8–5.6 vs 1.7– 1.9 mm in L. anteporus), higher ratio of a (40–50 vs 37–40 in L. anteporus) and b (16–17 vs 8 in L. anteporus), position of secretory-excretory pore (at or slightly anterior or posterior to nerve ring vs well anterior to nerve ring in L. anteporus), longer spicules (70–81 vs 33 µm) and shorter cephalic and outer labial setae (10–25 vs 35 µm in L. anteporus), from L. bocki in lower ratio of a (40–50 vs 75–88 in L. bocki), position of secretory-excretory pore (at or slightly anterior or posterior to nerve ring vs halfway between nerve ring and anterior body extremity in L. bocki), and presence of precloacal papillae and caudal setae (vs absent in L. bocki), from L. brevisetosus in shorter body length (3.8–5.6 vs 8.6 mm in L. brevisetosus), lower ratio of a (40–50 vs 119), b (16–17 vs 25 in L. brevisetosus), and c (8–11 vs 18 in L. breviseosus), and in tail shape having (elongated conicocylindrical vs short and conical in L. brevisetosus), from L. caxinus in longer body length (3.8–5.6 vs 1.5–2.1 mm in L. caxinus), lower ratio of a (40–50 vs 58–73 in L. caxinus), shorter cephalic and outer labial setae (10–25 vs 36–40% cbd in L. caxinuss) and longer spicules (70–81 vs 16–20 µm in L. caxinus), from L. conicaudatus in lower ratio of a (40–50 vs 60–61 in L. conicaudatus), shorter cephalic and outer labial setae (10–25 vs 30% cbd in L. conicaudatus) and tail shape (elongated conicocylindrical vs short and conical), from L. deconincki in the lower ratio of a (40–50 vs 64–82 in L. deconincki), position of vulva (49–55 vs 44% of body length from anterior in L. deconincki), number of precloacal supplements (25–27 vs 10 in L. deconincki) and larger amphid (35–42 vs 28% cbd in L. deconincki), from L. ordinarius in the lower ratio of a (40–50 vs 90–95 in L. ordinarius) and b (16–17 vs 13– 14 in L. ordinarius), slightly shorter cephalic and outer labial setae (10–25 vs 27–30% cbd in L. ordinarius), larger amphids (35–42 vs 30–33% cbd in L. ordinarius), and buccal cavity armature (strongly cuticularized vs not cuticularized in L. ordinarius), and from L. undulatus in longer body longer length (3.8–5.6 vs 2.3 mm in L. undulatus), tail shape (conicocylindrical without subventral papillae vs conical with seven pairs of subventral papillae in L. undulatus), and larger amphid (35–42 vs 25% cbd in L. undulatus). Etymology The species name is derived from the Greek ʻ pycnos ʼ (= dense, thick) and ʻ krikos ʼ (= ring), and refers to the thickly cuticularized amphideal fovea of the species. Material examined Holotype NEW ZEALAND • ♂; Hikurangi Margin, Uruti South cold seep site; 41.4251° S, 176.3510° E; 1227 m water depth; collected on 13 Jul. 2019; sandy mud (96% silt/clay, mean particle size 17 µm), voyage TAN1904, station 61; NIWA 154906. Paratypes NEW ZEALAND – Uruti South cold seep site • 1 ♂; 41.4250° S, 176.3510° E; 1226 m depth, collected on 13 Jul. 2019; voyage TAN1904, station 62; NIWA154908 • 1 ♀; 41.4279° S, 176.3485° E; 1245 m depth, collected on 14 Jul. 2019; sandy mud (97% silt/clay, mean grain size 14.2 µm), voyage TAN1904, station 64; NIWA154910 • 3 ♂ ♂; 41.4266° S, 176.3497° E; 1230 m depth, collected on 14 Jul. 2019; sandy mud (97% silt/clay, mean grain size 19 µm); voyage TAN1904, station 66; NIWA154907 • 2 ♀ ♀; 41.4260° S, 176.3506° E; 1237 m depth, collected on 14 Jul. 2019; sandy mud (94% silt/clay, mean grain size 18 µm); voyage TAN1904, station 68; NIWA154909. Type habitat and locality New Zealand continental slope, Hikurangi Margin, Uruti South cold seep. Description Male Body mostly colourless except for slight brown colouration in pharyngeal region and presence of brown granules in intestine wall, cylindrical, tapering slightly towards both extremities. Cuticle finely striated, no lateral differentiation. Somatic setae apparently absent. Blunt to rounded cephalic region, not set-off from rest of body. Narrow mouth opening surrounded by bulge of inner portion of lip region. Six minute inner labial papillae surrounding mouth opening. Six outer labial setae, 5–6 µm or 17–25% cbd long, situated at same level as four slightly shorter cephalic setae; 3–4 µm or 10–16% cbd. Six additional setae present at same level as cephalic and outer labial setae in most specimens; additional setae similar in length to outer labial setae or slightly shorter, situated laterally, lateroventrally and laterodorsally, resulting in a 6 + 16 arrangement of cephalic sensilla. Eight subcephalic setae present, 4–6 µm long; two subdorsal and two subventral setae situated at level of amphid, and two sublateral setae located slightly posterior to each amphid. Amphidial fovea circular; outline strongly cuticularized, usually with pitted appearance in centre, surrounded by cuticle striations, ca 0.3–0.4 cbd from anterior extremity. Buccal cavity cup-shaped, 10–15 µm deep, up to 15 µm wide, with strongly cuticularized base and walls; teeth-like projections not observed. Ducts of pharyngeal glands visible, emptying at base of buccal cavity. Pharynx muscular, anterior portion surrounding base of buccal cavity, not swollen; posterior portion of pharynx slightly swollen but not forming a true bulb. Nerve ring located near middle of pharynx or slightly anteriorly or posteriorly. Secretory-excretory system present, small ventral gland situated at level of cardia; excretory pore located at level of nerve ring or immediately posterior or anterior to it. Cardia well-developed, 43–93 µm long. Reproductive system with two opposed testes; outstretched anterior testis, posterior testis may be oustretched or reflexed.Anterior and posterior located either both to the right or both to the left of intestine. Sperm cells globular, 17–20 × 18–23 µm. Spicules short, arcuate, 0.9–1.1 cloacal body diameters long, strongly cuticularized, tapering distally. Gubernaculum with straight dorsocaudal apophyses. Twentyfive to twenty-seven papilliform precloacal supplements, beginning 15–30 µm anterior to cloaca and 9–28 µm apart. Tail conicocylindrical, with short subventral setae on anterior conical portion; terminal setae not observed. Caudal glands not well defined. Female Similar to males but with fewer caudal setae. Reproductive system with two opposed outstretched ovaries both located to the left of intestine. Spermatheca not observed. Vulva located near mid-body. Vaginal glands present. Pars proximalis vaginae surrounded by constrictor muscle.

Published as part of Leduc, Daniel, 2023, New nematode species and genera (Nematoda: Chromadorea) from cold seeps on Hikurangi Margin, New Zealand, pp. 1-45 in European Journal of Taxonomy 856 on pages 10-16, DOI: 10.5852/ejt.2023.856.2025, http://zenodo.org/record/7522913