Molgolaimus haakonmosbiensis, Portnova, 2009

Portnova, Daria, 2009, Free-living nematodes from the deep-sea Håkon Mosby Mud Volcano, including the description of two new and three known species *, Zootaxa 2096 (1), pp. 197-213 : 207-209

Molgolaimus haakonmosbiensis sp. n.

Figures 4 , Table 5

Type material: five males, three females. Glycerine slides. Holotype: male in glycerin slide No. D-1/18–1. Paratypes: males, nos. from D-1/18 to D-1/20; females, nos. from D-1/19 to D-1/21.

Type locality: Norwegian Sea, Håkon Mosby Mud Volcano, stations 283A, 283B. Sediment from the pogonophoran fields.

Etymology: referring to the Håkon Mosby Mud Volcano.

Description: Body short, cylindrical. Cuticle finely striated, striation especially visible on the tail. Cuticle thickens at the head. Head small and wide, separated from body by small narrowing before head setae. Inner and outer labial sensilla indistinct.

Four cephalic setae 3–4 µm long, arranged slightly over the cephalic constriction. Amphidial fovea circular, distinctly sclerotized, 5–6 µm in diameter (45–50 % of c.b.d.). Distance from apex to anterior border of amphidial fovea 10–11 µm, identical for males and females. No somatic setae along the body.

Stoma small, very narrow, weakly sclerotized, without teeth. Oesophagus narrow, cylindrical, and muscular along its entire length, posteriorly forming a pronounced spherical bulb. Diameter of the bulb 20 µm. Intestine gleam well looked through. Cardia small and extended.

Glandular body of the renetta cell porrect, lies below cardia at the ventral side of the body. Excretory pore located between the nervous ring and bulb.

Male reproductive system monorchic. Outstretched testis situated to the left of intestine. Vas deferens long and thin. Spermatozoa oval and trapezium-shape filling the testes very dense.

Spicules short, thin, flexuous, ventrally bent, with dilated and excurved proximal parts. Length of spicules 30.5 µm (arch), and 24.4 µm (chord). Relation of spicules length vs. a.b.d. 1.32–1.45.

Gubernaculum with thin, long, claw–like, hamose front apophysis. Length of apophysis 12.2 µm. The two precloacal papilla formed supplements with short terminal setae present in all males. Distance between anus and nearest supplement 12.2 µm. Distance between two supplements 6.1 µm.

Female reproductive system didelphic, with reflexed ovaries. Anterior ovary slightly longer than posterior one. The ovaries located to the left of the intestine. A formed egg well visible only in a single female, its diameter in the oviduct is 23 µm.

Tail conical, evenly tapering. Relation of spicules length vs. a.b.d. is 2–2.9. Relation of body length vs. spicules length is 17.5–20. Relation of the tail length vs. spicules length/a.b.d. is 42.2–46.3. The row of somatic setae 1–2 µm long present at the ventral side of the tail.

Diagnosis: Short body length (550.8–612 µm), relatively large head diameter (7–9 µm). Cuticle finely striated. Amphidial fovea circular, distinctly sclerotized. Stoma small, narrow, without teeth. Oesophagus narrow, posteriorly forming a pronounced spherical bulb. Female reproductive system didelphic, both ovaries reflexed, located to the left of intestine. Monorchic, outstretched testis. Slender short spicules with amplated and excurved proximal parts. Clawform and hamose front apophysis. Two precloacal supplements. Tail conical.

Discussion: Based on the set of measurements, specimens from Håkon Mosby Mud Volcano belong to group 1a sensu Fonseca et al. (2006). New species differs from 5 known species of the group 1a by length and form of spicules and apophyses. M. citrus Gerlach, 1959 and M. lazonus Vitiello, 1971 have more straight and short (15 µm and 21 µm vs. 30.5 µm) spicules. In M. turgofrons Lorenzen, 1972 and M. cuanensis Platt, 1973 the body is longer than in the new species (746 µm and 1200–1500 µm vs. 536–612 µm). M. lazonus Vitiello, 1971 and M. turgofrons Lorenzen, 1972 lack the precloacal supplements. M. parallgeni Vitiello and Boucher, 1971 differs from the new species by having longer cephalic setae (6 µm vs. 3–4 µm) and more curved spicules.

The new species resembles M. exceptionregulum Fonseca et al., 2006 in the ratio of body length to spicules length. However, M. exceptionregulum differs from M. haakonmosbiensis sp.n. by the form of spicules (with a pronounced capitulum and ventrally curved blade), longer gubernaculum (19 µm vs. 12.2 µm), presence of only one precloacal supplement and digitate prolongation on its tail.

Figures

FIGURE 4. Molgolaimus haakonmosbiensis sp. n., details. A: holotype male, total view; B: holotype male, cloacal region; C paratype female, total view; D paratype female, cephalic region. Scale bars: 50 µm