Microlaimus discolensis Bussau et Vopel, 1999

Miljutin, Dmitry M. & Miljutina, Maria A., 2009, Deep-sea nematodes of the family Microlaimidae from the Clarion-Clipperton Fracture Zone (North-Eastern Tropic Pacific), with the descriptions of three new species *, Zootaxa 2096 (1), pp. 137-172 : 157-161

Microlaimus discolensis Bussau et Vopel, 1999

( Figs 13–16 , Table 5)

Material examined: 1 male, 3 females ( Table 5)

Locality: Tables 1, 5.

Measurements: Table 5.

Description of male: Body cylindrical, with slightly narrowed anterior end and conical tail. Cuticle annulated. Annuli beginning posterior to cephalic capsule (width of every annulus 1.2 µm). Cuticle thickness 0.9 µm at level of cephalic capsula, and 1.2 µm at rest body. Four submedian rows of short cylindrical tubes 1 µm long and 1–1.5 µm in their diameter with pores on its tips situated along whole body. Almost every pore associated with large hypodermal gland 4–8 µm in diameter. The number of tubes in dorsolateral rows 3.5 times more than in ventrolateral ones. The content of glands depending on their size. Smaller glands containing fine-grained content, whereas content of bigger glands being coarse-grained. The anteriormost group of 4 tubes situated at the level of posterior rim of amphidial fovea. The posteriormost tube of dorsolateral rows situated at middle of tail; posteriormost tube of ventrolateral rows located behind anus. Location of tubes in rows not absolutely regular, e.g. distance between tubes varying. Tubes of ventrolateral rows situated more sparsely at region of midbody. Four somatic setae of 3 µm length visible at caudal region. No other somatic setae found. Head sensilla arranged in three circles: 6 inner labial papillae 2 µm long of first ring; 6 thick outer labial setae 6 µm long of second one; 4 cephalic setae 6 µm long of third circle situated near posterior border of cephalic capsule. Amphidial fovea monospiral, round, 59% of c.b.d. in diameter. The amphidial aperture less in diameter than subcuticular amphidial fovea. There are 4.5 cuticular annules between anterior rim of amphid and cephalic capsule. Vestibulum short, bowl-shaped, possessing 12 cuticularized ribs. One big dorsal sclerotized tooth visible in stegostoma. Pharynx thick, muscular, its anterior part at level of stoma slightly set off from its more posterior part. Well-developed terminal pear-shaped bulb about 1/3 of c.b.d. in its width present. Nerve ring not found. Renetta with large cellular body located at level of beginning of intestine. Its outlet opening not visible. Cardia short. Reproductive system diorchic, with opposite outstretched testes. Posterior testis shorter then anterior one. The anterior one lies to the right of intestine, and posterior one lies to the left. Vas deferens thick, 26% of total body length, filled with spermatids with coarse-grained content. Spicules rather large and curved. Gubernaculum rod-like. Supplementary organs not found. Whole reproductive system occupying approximately 1/2 of total body length. Tail conical, with protruded tip. Caudal gland not found.

Female: Females resembling male but differing in some parameters, such as their amphids being smaller (41–44% of c.b.d.). There are 6 cuticular annules between anterior rim of amphid and cephalic capsule of all female individuals. Posteriormost pore of ventrolateral rows situated before anus. Number of pores in rows varying in different specimens from 35 to 40 in dorsolateral rows and from 9 to 13 in ventrolateral rows. Number of pores in dorsolateral rows in 2.6–4.0 times more than in ventrolateral ones. There are only a few pores associated with hypodermal glands. Glands being bigger then males ones (up to 2/3 of c.b.d. in its diameter) and possessing more coarse-grained content. Somatic setae not found. Reproductive system didelphic, amphidelphic, with outstretched ovaries, occupying 2/5 of total body length. Anterior ovary lying to the left of intestine and posterior one lying to the right. Posterior ovary containing one mature elongated oocyte 69 µm long. Spermatozoa 3x12 µm in size visible in uterus. Vulvar glands not visible.

Abundance: The average density of this species was 0.03 inds/ 10cm 2. The relative abundance of this species within the nematode community was 1–2% at the stations where it was found.

Remarks: This species was initially found in the Peru Basin (the South Pacific), at a depth of 4100–4200 m, in ooze containing nodules (cauliflower type nodules) ( Bussau & Vopel 1999). Our find is the second record of M. discolensis . The place of new finding locates about 5200 km NM far from the place where the type specimens were found. Environments of the CCFZ are similar to that in the Peru Basin, but the depth of the new finding was about 1 km deeper. Two of our individuals were found in sediment with nodules and two other in the area adjacent to nodule field.

The new specimens fit very well the original description as no strong differences were found.

Figures

FIGURE 13. Microlaimus discolensis, specimen No. 1, male, total view. Scale bar = 100 µm.

FIGURE 14. Microlaimus discolensis, specimen No. 1, male. A, anterior end; B, posterior end. Scale bars = 20 µm.

FIGURE 15. Microlaimus discolensis, females. A, specimen No. 3, total view; B, specimen No. 3, head; C, specimen No. 2, dorsal pore and associated gland. Scale bars: A = 50 µm; B = 20 µm; C = 10 µm.

FIGURE 16. Microlaimus discolensis, light micrographs. A, specimen No. 1, male, head; B, specimen No. 1, male, region of pharyngeal bulb; C, specimen No. 1, male, dorsolateral row of pores; D, female No. 3, dorsolateral row of pores (marked by arrows) and associated glands; E, specimen No. 1, male, ventrolateral row of pores; F, specimen No. 1, male, anal region, optical section at level of gubernaculum; G, No. 1, male, anal region, optical section at level of distal part of spicules. Scale bars: A, E–G = 10 µm; B–D = 20 µm.