Siphonolaimus curtisensillus, Leduc, 2023

Leduc, Daniel, 2023, New nematode species and genera (Nematoda: Chromadorea) from cold seeps on Hikurangi Margin, New Zealand, European Journal of Taxonomy 856, pp. 1-45 : 4-9

Siphonolaimus curtisensillus sp. nov.

urn:lsid:zoobank.org:act:CDE73FE3-042C-4089-B4B2-3FB5DE579F4A

Figs 1–3 , Table 2

Diagnosis

Siphonolaimus curtisensillus sp. nov. is characterized by body length 3.5–5.3 mm, papillose outer labial sensilla, short cephalic setae (3 µm or 0.21–0.27 cbd), 2–3 µm long subcephalic setae, amphids 36–41% cbd wide, arcuate spicules 1.2–1.7 cloacal body diameters long, gubernaculum with sharply bent crurae and dorsocaudal apophyses, at least 30 inconspicuous precloacal supplements, vulva located at 68–76% of body length from anterior extremity, uterus wall slightly cuticularized opposite vulva, and tail conical and gradually tapering.

Differential diagnosis

The new species is most similar to S. banyulensis Boucher, 1971 (known only from males), S. mejillinus Pastor de Ward, 1989 and S. japonicus Zograf, Trebukhova & Pavlyuk, 2015 in having papillose outer labial sensilla as well as short (<0.3 cbd) cephalic setae. Siphonolaimus curtisensillus sp. nov can be differentiated from S. banuylensis by the shorter body length (in males: 3.5–5.3 vs 7.8–8.3 mm in S. banyulensis ), shorter spicules (1.2–1.7 vs 3.0–3.7 cloacal diameters in S. banyulensis ), and longer tail (in males: 2.8–4.0 vs 1.5–1.8 cloacal body diameters in S. banyulensis ), from S. mejillinus by the shorter body length (3.5–5.3 vs 7.0– 8.3 mm in S. mejillinus ), larger amphids (36–41 vs 18–19% cbd in S. mejillinus ), and tail shape (elongated conical vs short and rounded in S. mejillinus ) and from S. japonicus by the higher a ratio (a = 63–76 vs 32–55 in S. japonicus ), longer siphon (44–64 vs 32– 41 µm in S. japonicus ), longer tail (cʹ = 2.8–5.6 vs 2.0– 2.3 in S. japonicus ) and number of precloacal supplements (at least 30 vs 15 in S. japonicus ).

Etymology

The species name is derived from the Latin ʻ curtus ʼ meaning ʻshortʼ and diminutive of Latin ʻ sensus ʼ meaning ʻperceiveʼ, ʻfeelʼ, and refers to the short cephalic sensilla characteristic of the species.

Material examined

Holotype NEW ZEALAND • ♂; Hikurangi Margin , Mungaroa cold seep site; 41.9382° S, 175.3128° E; 2076 m water depth; collected on 7 Jul. 2019; sandy mud (96% silt/clay, mean particle size 20 µm), voyage TAN1904, station 21; NIWA 154903 .

Paratypes NEW ZEALAND • 1 ♂, 2 ♀ ♀; same collection data as for holotype; NIWA154904 • 1 ♂, 2 ♀ ♀; Hikurangi Margin, Mungaroa cold seep site; 41.9378° S, 175.3112° E; 2075 m water depth; collected on 7 Jul. 2019; sandy mud (97% silt/clay, mean particle size 15 µm), voyage TAN1904, station 18; NIWA 154905 .

Type habitat and locality

New Zealand continental slope, Hikurangi Margin, Mungaroa cold seep.

Description

Male

Body colourless, long, cylindrical, tapering slightly towards both extremities. Cuticle with fine transverse striations without lateral differentiation. A few sparse, short somatic setae, ca 2 µm long, present in pharyngeal and posterior body regions. Cephalic region slightly rounded, no lip region visible. Inner labial papillae not observed; six short outer labial papillae, 1.5–2.0 µm long, at about same level as four slightly longer cephalic setae, 3 µm long (0.21–0.27 cbd). Ring of eight short subcephalic setae, 2–3 µm long, slightly anterior to amphid, and two subcephalic setae located ventrally and dorsally at level of amphid. Amphideal fovea circular with slightly cuticularized outline, situated 0.7–0.8 cbd from anterior end. Buccal cavity with spear-like siphon, 44–64 µm long or 26– 33% of pharynx length. Pharynx cylindrical, muscular, with elongated posterior bulb; pharyngeal lumen not cuticularised. Nerve ring at 60–65% of pharynx length from anterior. Secretory-excretory system present; pore located at or immediately posterior to level of nerve ring, ampulla small, renette cell not observed. Cardia small, 11–13 µm long, partially surrounded by intestine. Intestine wall consists of numerous clear cells each with nucleus.

Reproductive system monorchic with single anterior outstretched testis. Position of testis relative to intestine could not be determined. Sperm cells globular, 15–19 × 14–16 µm. Spicules paired, curved, tapering distally, 1.2–1.7 cloacal body diameters long. Gubernaculum with sharply bent lateral pieces (crurae) and almost straight dorso-caudal apophyses. Two rows of 10–13 ejaculatory glands located on either side of vas deferens. At least 30 inconspicuous papillose precloacal supplements present, located 18–22 µm apart. Tail conical, gradually tapering distally, 2.8–4.5 cloacal body diameters long; a few short and sparse somatic setae present subventrally and subdorsally. Caudal glands and spinneret not observed.

Females Similar to males, but with slightly longer tail, 4.4–5.6 anal body diameters long. Reproductive system monodelphic with single anterior ovary located to the left of intestine; mature eggs ca 135 × 42 µm. Spermatheca present posterior to vulva. Vulva situated slightly posterior to two thirds of body length from anterior extremity. Proximal portion of vagina surrounded by constrictor muscle, vaginal glands not observed. Proximal portion of uterus opposite vulva slightly cuticularized over ca two corresponding body diameters.

Figures

Fig. 1. Siphonolaimus curtisensillus sp. nov. A, C. Holotype (NIWA154903). B, D, Paratype (NIWA 154904). E. Paratype (NIWA154905). A. Male anterior body region. B. Female anterior body region. C. Male posterior body region. D. Female posterior body region. E. Male posterior body region. Scale bar: A–B = 75 µm; C = 70 µm; D = 85 µm; E = 125 µm.

Fig. 2. Siphonolaimus curtisensillus sp. nov. A. Entire male, holotype (NIWA154903). B. Entire female, paratype (NIWA154904). Scale bar = 400 µm.

Fig. 3. Siphonolaimus curtisensillus sp. nov. Light micrographs. A–B, F. Holotype (NIWA154903). C. Paratype (NIWA154905). D–E, G. Paratype (NIWA154904). A. Male cephalic region showing pharynx and stylet. B. Male cephalic region showing amphid. C. Female anterior body region. D–E. Male intestine. F. Copulatory apparatus. G. Vulva and proximal portion of female genital branch. Scale bar: A–B = 20 µm; C–F = 10 µm; G = 15 µm.