Choanolaimus sparsiporus, Leduc & Zhao, 2025

Leduc, Daniel & Zhao, Zeng Qi, 2025, Three new nematode species (Chromadorida: Selachinematidae) from the continental slope of New Zealand, European Journal of Taxonomy 989, pp. 119-143 : 129-131

Choanolaimus sparsiporus sp. nov.

urn:lsid:zoobank.org:act:A926DC8A-6F55-4D7B-A79A-AE31E6FF5C14

Fig. 5 ; Tables 2–3

Diagnosis

Body length 1272 µm, large amphidial fovea, 0.56 cbd wide and with 5¼ turns, pharynx with posterior bulb, two dorsosublateral rows of small pore complexes sparsely distributed between pharyngeal and tail regions, spicule length ca 1.5 body diameters at level of cloacal opening, gubernaculum 24 µm long, two papilliform precloacal supplements, tail short, conical, 1.1 body diameters long at level of cloacal opening.

Differential diagnosis

The new species is most readily distinguished from Choanolaimus psammophilus by the large amphidial fovea 0.56 cbd wide with 5¼ 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 ), pharynx with posterior bulb (vs pharynx without posterior bulb in C. psammophilus ), longer spicules (1.5 vs <1.0 body diameters at cloacal opening in C. psammophilus ) and fewer precloacal supplements (2 vs 6–7 in C. psammophilus ).

Choanolaimus sparsiporus sp. nov. can be distinguished from C. serieporus sp. nov. by the slightly shorter body (1272 vs 1321–1682 µm in C. serieporus ), higher a ratio (24 vs 17–18 in C. serieporus ), lower b and c ratios (8 and 27 vs 11 and 32–38, respectively, in C. serieporus ), arrangement of pore complexes (sparsely distributed vs groups of 8–11 pore complexes in C. serieporus ), and number of precloacal supplements (two vs 3–4 in C. serieporus ).

Etymology

The species name is derived from the Latin ‘ sparsus ’ (= ‘few, rare, scattered’) and ‘ porus ’ (= ‘hole’) and refers to the scattered arrangement of the pore complexes in this species.

Type material examined

Holotype NEW ZEALAND • ♂; Otago Fan complex, continental slope ; 46.4971° S, 170.8644° E; 992 m water depth; 13 Feb. 2024; voyage TAN2402, stn 34; NIWA 181632 .

Type habitat and locality

Continental slope, New Zealand.

Description

Male

Body cylindrical, tapering slightly towards both extremities, mostly colourless except for light brown intestine wall. Cuticle 3.0–3.5 µm thick, without annulations; transverse rows of cuticle punctations with lateral differentiation consisting of larger, more widely spaced punctations beginning from posterior to amphids to tail region. Two dorsosublateral rows of small pore complexes sparsely distributed between pharyngeal and tail regions; each pore complex ca 1.5 µm in diameter. Somatic setae short, 2.0–2.5 µm long, sparse, located dorsosublaterally and ventrosublaterally. Cephalic region somewhat rounded; lip region short, bearing six inner labial papillae. Six short outer labial papillae located slightly further posteriorly, ca 1.5–2.0 µm long, at same level as four cephalic papillae of same length. Amphidial fovea large, multispiral with 5¼ turns, situated ca 0.3 cbd from anterior end. Buccal cavity (pharyngostome) large, divided into anterior (gymnostome) and posterior portions (stegostome). Anterior portion of buccal cavity cup-shaped, 13 µm deep, with three sets of three cuticularised rhabdions, 11 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, 14 µm long. Pharynx 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, pore situated slightly posterior to nerve ring. Cardia small, 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 of intestine. Sperm cells spherical to globular, larger in anterior testis (11× 11– 14 µm) relative to posterior testis (6 ×6 µm). Spicules paired, curved, tapering distally, length 1.5 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. Two precloacal supplements present, consisting of small papillae on swollen portion of cuticle and connected to a hypodermal gland; posteriormost supplement 17 µm from cloaca, supplements 7 µm apart. Tail short, conical, rounded distally, cuticle gradually doubling in thickness posteriorly, reaching 10 µm thick distally; a few short and sparse somatic setae present. Three caudal glands, one of which extends well anterior to cloacal opening; spinneret present.

Figures

Fig. 5. Choanolaimus sparsiporus sp. nov., holotype, ♂ (NIWA 181632) A. Anterior body region. B. Posterior body region. C. Entire specimen. Arrows show position of dorsosublateral pore complexes. Scale bar: A = 75 µm; B = 60 µm; C = 200 µm.