Manganonema rowdeni, Leduc, Daniel, 2015

Leduc, Daniel, 2015, One new genus and five new nematode species (Monhysterida, Xyalidae) from Tonga and Kermadec Trenches, Southwest Pacific, Zootaxa 3964 (5), pp. 501-525 : 518

Manganonema rowdeni n. sp.

( Fig 10 )

Measurements. See Table 2.

Type specimens. Holotype male ( NIWA 100187), collected 6 May 2014 ( WHOI cruise TN309, Nereus dive N074). One paratype male and two paratype females ( NIWA 100187), collected 6 May 2014 ( WHOI cruise TN309, Nereus dive N074).

Type habitat. Kermadec Trench (178.17571º W, 34.34030º S), water depth: 8081 m, sediment depth 1–4 cm.

Etymology. This species is named after deep-sea benthic ecologist Ashley Rowden, principal investigator of the HADES project (HADal Ecosystem Studies) and participant on RV Yokosuka cruise YK13-10 to Tonga Trench.

Description. Males. Body long, cylindrical, widest in region immediately posterior to pharynx, and tapering slightly towards anterior and posterior extremities. Striated cuticle, ~1.1–1.4 µm thick. Several groups of epidermal cells, arranged in longitudinal rows of up to about twelve cells, present underneath cuticle, sometimes causing slight bulge in body outline ( Fig. 10 B). Anterior extremity dummy-shaped, with narrow, rounded, and slightly swollen head set off from rest of body by slight constriction, sometimes bent slightly. Somatic setae short and sparse, situated latero-ventrally and latero-dorsally; one pair of short, 1–2 µm long sub-cephalic setae, one situated latero-ventrally and the other latero-dorsally, immediately posterior to each amphideal fovea. Six minute inner labial papillae; six outer labial setae and four cephalic setae of similar length in one circle, 2–3 µm long. Mediumsized amphideal fovea, circular to oval-shaped, with cuticularised outline. Pharynx muscular with oval posterior bulb; cardia small. Nerve ring situated slightly posterior to half of pharynx length from anterior. Secretoryexcretory system not observed. Tail conico-cylindrical, with gradually tapering distal end. Three caudal glands and a few short caudal setae present.

Male reproductive system diorchic with two opposed and outstretched testes; anterior testis to the left of intestine and smaller posterior testis to the right of intestine. Sperm cells small, spherical to globular, ~2 × 2–3 µm. Spicules very thin, 0.95 abd long, tapering distally. Gubernaculum and pre-cloacal supplements/setae not observed. Females. Similar to males but with longer body and slightly higher values of a, b, and c. Reproductive system monodelphic with single anterior outstretched ovary situated to the left of intestine. Vulva situated at almost two thirds of body length from anterior; pars proximalis vaginae surrounded by thin constrictor muscle.

Diagnosis. Manganonema rowdeni n. sp. is characterised by long body (1298–1873 µm), presence of short somatic setae and one pair of sub-cephalic setae immediately posterior to each amphideal fovea, medium-sized amphideal fovea (0.50 abd), presence of two opposed testes and needle-like spicules in males, and conicocylindrical tail 3.6–5.0 abd long.

Differential diagnosis. Manganonema rowdeni n. sp. can be differentiated from most other species of the genus except M. kitasatoi n. sp. and M. majusculum n. sp. by the long body (>1100 µm), presence of a pair of subcephalic setae posterior to each amphideal fovea, and presence of two testes. Manganonema rowdeni n. sp. can be distinguished from the former by the presence of somatic and caudal setae (absent in M. kitasatoi n. sp.), amphideal fovea size (0.47–0.50 vs 0.65–0.81 cbd), tail length (3.6–5.0 vs 5.1–6.8 abd), and spicule length and shape (0.95 vs 0.45–0.54 abd; needle-shaped vs conical). M. rowdeni n. sp. can most easily be distinguished from M. majusculum n. sp. by the smaller amphideal fovea (0.47–0.50 vs 0.71–0.75 cbd), and shorter tail (3.6–5.0 vs 10.5–15.0 abd).

Figures

FIGURE 10 Manganonema rowdeni n. sp. A: Anterior body region of male holotype; B: female paratype anterior body region; C female paratype reproductive system; D: entire male holotype; E: male holotype posterior body region. Arrow shows position of spicule. Scale bar: A & B = 38 µm; C = 45 µm; D = 190 µm; E = 30 µm.