Choanolaimus serieporus Leduc & Zhao, 2025, sp. nov.

Choanolaimus serieporus sp. nov. urn:lsid:zoobank.org:act: A9649261-CB22-4A83-80EA-32AC1DD3839A Figs 2–4; Tables 2–3 Diagnosis Body length 1321–1688 µm, cephalic region with slight constriction at level of amphids, amphidial fovea large, 0.51–0.56 cbd wide and with 4–5 turns, short pharynx with posterior bulb, each side of body with two to three groups of 8–11 dorsosublateral pore complexes arranged in longitudinal rows and located between pharyngeal and tail regions, spicule length 1.2–1.6 body diameters at level of cloacal opening, gubernaculum 36 µm long, three or four precloacal supplements, tail short and rounded, 0.7 body diameters long at level of cloacal opening in males. Differential diagnosis The new species is most readily distinguished from Choanolaimus psammophilus by the large amphidial fovea 0.51–0.56 cbd wide with 4–5 turns (vs amphidial fovea <0.3 cbd wide with 2–2¼ turns in C. psammophilus), arrangement of pore complexes (dorsosublateral vs dorso- and ventrosublateral in C. psammophilus), shape of the inner labial sensilla (papilliform vs ‘flap-like’ or on swollen lobes in C. psammophilus), short 125–155 µm long pharynx with posterior bulb (vs pharynx> 200 µm long without posterior bulb in C. psammophilus), longer spicules (1.1–1.6 vs <1.0 body diameters at cloacal opening in C. psammophilus) and fewer precloacal supplements (3–4 vs 6–7 in C. psammophilus). Choanolaimus serieporus sp. nov. can be distinguished from C. sparsiporus sp. nov. by the slightly longer body (1321–1682 vs 1272 µm in C. sparsiporus), lower a ratio (17–18 vs 24 in C. sparsiporus), higher b and c ratios (11 and 32–38 vs 8 and 27, respectively, in C. sparsiporus), arrangement of pore complexes (groups of 8–11 pore complexes vs sparsely distributed in C. sparsiporus), and number of precloacal supplements (3–4 vs 2 in C. sparsiporus). Etymology The species name is derived from the Latin ‘ series ’ (= ‘row, succession’) and ‘ porus ’ (= ‘hole’) and refers to the arrangement of the pore complexes in rows in this species. Type material examined Holotype NEW ZEALAND • ♂; Otago Fan complex, Papanui Canyon; 45.8668° S, 171.0415° E; 680 m water depth; 9 Feb. 2024; sandy mud sediments; voyage TAN2402, stn 2; NIWA 181629. Paratypes NEW ZEALAND • 1 ♂; Otago Fan complex, continental slope; 46.9320° S, 171.7847° E; 1338 m water depth; 14 Mar. 2019; voyage TAN1902, stn 130; NIWA 181630 • 1 ♀; Challenger Plateau, continental slope; 30.6450° S, 172.1533° E; 266 m water depth; 7 Jun. 2007; voyage TAN0707, stn 134; NIWA 181631. Type habitat and locality Continental slope, New Zealand. Description Males Body cylindrical, tapering slightly towards both extremities, mostly colourless except for light brown intestine wall. Cuticle 3–4 µm thick, with faint annulations ca 2.0–2.5 µm apart; transverse rows of cuticle punctations with lateral differentiation consisting of larger, more widely spaced punctations beginning from about middle of pharynx length to proximal portion of tail. On each side of body, two to three groups of 8–11 dorsosublateral pore complexes arranged in longitudinal rows and located between pharyngeal and tail regions; each pore complex ca 1.5–2.5 µm in diameter. Somatic setae short, ca 2 µm long, sparse, irregularly arranged along body. Cephalic region slightly rounded, with slight constriction at level of amphids. Lip region short, slightly raised. Six inner labial papillae; six short outer labial papillae, ca 1.5–3.0 µm long, at same level as four cephalic papillae of same length. Amphidial fovea large, multispiral with 4¾–5 turns, situated ca 0.4 cbd from anterior end. Buccal cavity (pharyngostome) large, divided into anterior (gymnostome) and posterior portions (stegostome).Anterior portion of buccal cavity cup-shaped, 16–26 µm deep, with three sets of three cuticularised rhabdions, 14–21 µm long, terminating in three sets of small bifid teeth (denticles), with raised central denticle located in middle of each set; posterior portion of buccal cavity narrower, cylindrical, surrounded by three Y-shaped pairs of cuticularised rhabdions with swollen bases, of similar length to anterior rhabdions. Pharynx short, muscular, slightly swollen anteriorly and with posterior bulb; pharyngeal lumen not conspicuously cuticularised. Nerve ring near middle of pharynx length. Secretory-excretory system present; renette cell situated at level of cardia, ampulla small, pore situated immediately posterior to nerve ring. Cardia small, ca 6 µm long, partially surrounded by intestine. Posterior extremity of intestine blind, rectum absent. Reproductive system diorchic with opposed, outstretched testes. Anterior testis to the right of intestine, posterior testis to the left or ventrally relative to intestine. Sperm cells globular; in holotype, sperm cells of similar dimensions in both anterior and posterior testes (10–11 ×13–15 µm). In paratype, sperm cells markedly larger in anterior testis (14–16 ×17–24 µm) relative to posterior testis (6 ×10 µm). Spicules paired, curved, tapering distally, length 1.2–1.6 body diameters at level of cloacal opening; gubernaculum consisting of two detached lateral pieces (crurae) tapering distally, ca 0.4 spicule length, median portion of gubernaculum (corpus and cuneus) apparently absent. Three or four precloacal supplements present, consisting of raised areas of cuticle; posteriormost supplement 11–12 µm from cloaca, remaining supplements 8–13 µm apart. Tail short, rounded, cuticle gradually doubling in thickness posteriorly, reaching 7 µm thick distally; a few short and sparse somatic setae present. Three caudal glands located posterior to cloacal opening, spinneret present. Female Similar to males but amphids with 4 turns. Reproductive system didelphic-amphidelphic, with reflexed ovaries; anterior ovary to the right of intestine, posterior ovary to the left of intestine. Vulva situated near mid-body. Proximal portion of vagina surrounded by constrictor muscle, vaginal glands present. Intestine blind, anus absent.