Sabatieria megadena Leduc, 2017, sp. n.

Sabatieria megadena sp. n.

(Figs. 1–3, Table 1)

Diagnosis. Sabatieria megadena sp. n. is characterised by body length 2290–2890 µm, smooth cuticle without punctations or striations, spiral amphids with 2.0 turns, minute buccal cavity, secretory-excretory system with large and conspicuous renette cell, anterior branch of reproductive system always to the left of intestine and posterior branch always to the right of intestine, and male with arcuate spicules 1.1–1.5 cloacal body diameters long and six tubular precloacal supplements.

Etymology. The species name is derived from the Greek megas (=large, great) and adenos (= gland), and refers to the large size of the renette cell in this species.

Holotype. Male (NIWA 115450), collected April 2010 (voyage TAN1004, station 22), New Zealand’s Hikurangi Margin, axis of Pahaua Canyon (1188 m water depth), 41.5100°S, 175.7187°E, mean grain size: 11 µm, % silt and clay particles: 96.8%.

Paratypes. Two males and six females (NIWA 115451, NNCNZ 3252), same data as holotype.

Description. Males. Colourless cylindrical body tapering slightly towards anterior end, with rounded anterior extremity and conicocylindrical tail. Cuticle smooth with sparse somatic setae mainly restricted to pharyngeal region, 2–4 µm long. Two lateroventral rows of 3–4 setae in precloacal region. Six minute inner labial papilla present on lip region; six outer labial papilla in a separate circle and four cephalic setae situated further posteriorly, 0.20–0.25 cbd long. Subcephalic setae absent. Spiral amphideal fovea and aperture, with 2.0 turns, situated immediately posterior to cephalic setae. Buccal cavity minute. Cylindrical pharynx with oval-shaped posterior bulb; pharyngeal tubes present. Nerve ring near middle of pharynx length. Secretory-excretory system present, excretory pore slightly posterior to nerve ring, ampulla large; renette cell large and conspicuous, 24–32 × 55–85 µm, often associated with swelling of body, situated immediately posterior to pharynx. Cardia 15–17 µm long, not surrounded by intestine. Reproductive system diorchic with anterior outstretched testis located to the left of intestine and posterior outstretched testis to the right of intestine. Mature sperm cells globular, 4–7 × 8–11 µm, with oval nuclei. Spicules paired, equal, arcuate, 1.1–1.5 cloacal body diameters long, without capitulum, with velum and short central cuticularised projection (lamella) at proximal end. Gubernaculum surrounding distal ends of spicules, with pair of strongly cuticularised apophyses directed dorso-caudally or caudally, tapering distally. Rectal and ejaculatory glands not observed. Six tubular precloacal supplements present, situated 14–24 µm from each other. Precloacal seta not observed. Tail conicocylindrical, with distal tip sometimes slightly swollen, and with sparse lateroventral setae and three terminal setae. Three caudal glands and spinneret present.

Females. Similar to males, but with lower value of a, slightly smaller amphid, and slightly longer tail. Reproductive system didelphic, with anterior outstretched ovary to the left of intestine and posterior outstretched ovary to the right of intestine. Mature eggs 49–57 × 117–136 µm. Spermatheca not observed. Vulva located near mid-body. Granular vaginal glands present, proximal portion of vagina uterina surrounded by constrictor muscle.

Differential diagnosis. The new species is similar to the closely related genus Laimella Cobb, 1920 in the small size of the buccal cavity, amphids with few turns (<4), and cuticle without punctations; however unlike Laimella it does not possess a cuticularised pharyngeal lumen or teeth in the buccal cavity, and does not have outer labial setae in the same circle as the cephalic setae. Sabatieria megadena sp. n. is also similar to Cervonema Wieser, 1954 in lacking cuticle punctations and in the small size of the buccal cavity without teeth. However the new species, unlike Cervonema, does not have setiform outer labial sensilla similar in length to the cephalic setae, and possesses a gubernaculum with conspicuous apophyses.

Sabatieria megadena sp. n. resembles Sabatieria dispunctata Rosli, Leduc & Probert, 2014 (also described from New Zealand’s Hikurangi Margin), in lacking cuticle punctations and the minute size of the buccal cavity. The new species can most easily be distinguished based on the number of amphid turns (2.0 versus 4.5 turns in S. dispunctata), presence of large and conspicuous renette cell (versus substantially smaller renette cell in S. dispunctata), and length of the tail (3–5 versus 8 anal/cloacal body diameters in S. dispunctata). Like S. dispunctata, S. megadena sp. n. is placed within the genus Sabatieria despite its lack of cuticle punctations because it is characterised by four cephalic setae and six outer labial papilla in separate circles, a buccal cavity without teeth, short arcuate spicules, and gubernaculum with conspicuous apophyses. Several Sabatieria species, namely S. dodecaspapillata Kreis, 1929, S. longisetosa Kreis, 1929, and S. mortenseni Ditlevsen, 1921, also appear to lack cuticle punctations. In addition to the presence of minute buccal cavity and large and conspicuous renette cell, Sabatieria megadena sp. n. can most easily be distinguished from S. mortenseni and S. longisetosa by the amphids with fewer turns (2.0 versus > 3.0 turns in S. mortenseni and S. longisetosa), and from S. dodecaspapillata by the number of precloacal supplements (6 versus 12 in S. dodecaspapillata) and location of opening of secretoryexcretory system (posterior to nerve ring versus at level of nerve ring in S. dodecaspapillata).