Amphimonhystera molloyensis Tchesunov et Mokievsky

Tchesunov, Alexei V. & Mokievsky, Vadim O., 2005, A review of the enus Amphimonhystera Allgén, 1929 (Monhysterida: Xyalidae, Marine Freeliving Nematodes) with description of three new species, Zootaxa 1052, pp. 1-20 : 12-16

Amphimonhystera molloyensis Tchesunov et Mokievsky sp. n.

( Figures 4 A–E, 5 A–D & 6A–E)

Type material: Holotype male, three paratype males and two paratype females mounted in glycerin on glass slides. Type specimens is deposited in the collection of the P. P. Shirshov Institute for Oceanology, Russian Academy of Sciences, Moscow.

Labels: (Holotype male ref #1­1/4): RV Polarstern, ARK XVII st. 125, B(0 – 1 cm), 63 µm, 1/44; (Paratype male 1 and paratype female 1 ref # M­1/6): RV Polarstern, ARK XVII, st. 125, C (0–1 cm), 250 µm, 2/2; (Paratype male 2, ref # M­1/5): RV Polarstern, ARK XVI, St. 251, MD 316 (0–1 cm), 125 mkmµm, 1/13; (Paratype male 3, ref # M­1/3): RV Polarstern, ARK XVI, St. 251, MD 316 (0–1 cm), 125 mkm; (Paratype female 2, ref # M­1/7): RV Polarstern, ARK XVII, st. 125, C (0–1 cm), 125 µm, 2/44.

Type locality: Arctic Ocean, area between Greenland and Svalbard. Holotype: st.125, 79°12.0' N 02°34.5' E, 5416 m, (Molloy Deep), silt, 13 July, 2001; Paratypes: St.251, 79°8.2' N & 02°53.6' E, depth 5569 m (Molloy Deep), silt, 16 August, 2000; and st.125, 79°12.0' N 02°34.5' E, 5416 m, (Molloy Deep), silt, 13 July, 2001.

Etymology: The species name refers to the area of its findings, Molloy Deep. Morphometric data: Table 5 .

Specimens Holotype Paratypes

Label Male 1 Male 2 Male 3 Male 4 Female 1 Female 2 dist. tail portion (%) 28 34 29 36 32 28

termin s. 6.5 6.0 5.0 6.5 7.5 6.0 Description: Body slender, elongated spindle­shape, near cylindrical. Cuticle rather thin and finely transversely striated. In one specimen (ɗ2), subcuticular hypodermis yellow­brownish granules irregularly distributed throughout the body; pigment granules concentrated in preneural region (especially densely just posterior to the amphidial fovea) and thereafter less densely in posterior body region and tail, predominantly in ventral position. In other specimens, males and females as well, there are no conspicuous pigment granules in the anterior hypodermis. Labial region dome­shaped and slightly set off from the rest of the body. Inner labial sensilla not observed. Six outer labial sensilla and four cephalic sensilla setiform, and united with two additional lateral setae in one circle of twelve slender setae situated at the level of the stoma base. ɗ2 distinguished with shorter outer labial setae equal to cephalic setae and lacking additional setae. Amphidial fovea very large, longitudinally oval, with distinct cuticular edging; amphidial fovea of ɗ2 with a convex central spot. The cuticular edging marked with a slight break posteriorly in some specimens. The amphidial fovea situated relatively close to the anterior end. Somatic setae scarce and short, mostly in sublateral position. Buccal cavity small, with very weakly sclerotised walls. The cheilostoma forming the major part of the buccal cavity. The posterior stoma region or esophastoma very short, narrow and slightly asymmetrical. Esophagus uniform and weakly muscular, very slender, gradually widening to the cardia. Cardia internal. There is a thick dense internal lining in the midgut lumen. No indication of a renette cell. Anterior part of the female genital branch with germinal zone and smaller oocytes in two rows situated left of the intestine. Posterior part of the female branch with larger oocytes in one row folded ventrally to the right side of the intestine. The posteriormost part of the branch filled with small rounded spermatozoa. Vagina slanting and encircled by a strong sphincter. There are two sets of granular vulvar glands associated with the vagina, the anterior vulvar glands being much smaller than posterior ones. Five transparent ejaculatory glands visible at the left side of the ejaculatory duct of ɗ1. Spicules short, twice bent, distally acute and proximally cephalated. No gubernaculum.

Tail consisting of a proximal conical and a distal slender cylindrical part. Tail tip slightly widened and provided with two subterminal setae.

Remark: ɗ2 (paratype) is noticeably distinguished from other males and females by slightly shorter outer labial setae of the cephalic circle and intensive subcuticular pigmentation in the anterior body region ( Fig. 6 B–C). These differences may be connected with the locality of ɗ2, i.e. remote from the sites of other specimens.

Diagnosis: Body length 810–975 µm. Outer labial and cephalic setae 4.0–8.5 µm long. Amphidial fovea large, 15.5–18.0 µm long; ratio length to width of the amphidial fovea 1.55–1.67; distance from cephalic apex to anterior rim of the amphidial fovea rather short, 9.0–11.5 µm. Spicules 27.0–32.5 µm long. Terminal caudal setae 5.0–7.5 µm long.

Differential diagnosis: The new species shares with A. galea , A. marisalbi and A. pallida a relatively small body length (<1 mm) and tail shape with slender cylindrical portion bearing terminal setae. A. molloyensis sp. n. distinctly differs from both A. galea and A. pallida by very short setae of the cephalic circle and by proximal position of the amphidial fovea.

Figures

FIGURE 4. Amphimonhystera molloyensis sp. n., details. (A) male 1 (holotype), cephalic end; (B) female 1 (paratype), cephalic end; (C) female 1 (paratype), tail tip; (D) male 1 (holotype), copulatory apparatus; (E) female 2 (paratype), posterior uterus, vagina and vulvar glands. Scale bars: (A) – (E) 10 µ m.

FIGURE 6. Amphimonhystera molloyensis sp. n., paratype male 2. (A) entire; (B) esophageal region; (C) cephalic end; (D) tail region; (E) spicule. Scale bars: (A) 100 µ m; (B) & (D) 50 µ m; (C) & (E) 10 µ m.

Tables

TABLE 5. Morphometry of Amphimonhystera molloyensis sp. n.

Character	ARK XVII, st 125, B 0–1 cm, 63 µm, 1/44	ARK XVI, ARK XVII, st st 251 125, 0–1 cm, MD 316, 0–1 cm, 250µm, 2/2 125 µm, 1/ 2 (4)	ARK XVII, st ARK XVII, st 125, A 0–1 cm, 125, 0–1 cm, 125 µm, 1/13 250µm, 2/2	ARK XVII, st 125, C 0–1 cm, 125µm, 2/44
L	940	810 940	895 965	975
a	36.7	35.2 35.1	37.6 32.4	29.8
b c	5.3 6.8	5.2 6.1 6.6 6.6	5.7 5.8 6.7 6.5	5.9 7.1
V (%)	­	­ ­	­ 67.2	70.5
b.diam.c.s.	10	10 9	? 12	11
b.diam.am.	15	14 16	14 16	16
b.diam.n.r.	22	19 22	??	23
b.diam.c.	22	21 22	22 26	25
d iam.midb. a.d.	26 22	23 27 19 22	24 30 21 20	30 19
c.s.	6.5	4.0 5.0	? 8.5	5.0
c.s. (%)	65	40 56	? 71	48
am.l.	18.0	18.0 16.0	16.0 17.5	15.5
am.w.	?	??	10.0 10.5	10.0
am.w. (%)	?	??	74.1 67.7	62.5
am.l./am.w. dis.am.	? 9.0	?? 9.0 9.0	1.60 1.67 11.5 9.0	1.55 9.5
st.w.	5.0	4.0 5.5	6.0 5.5	7.0
st.l.	4	4 8	4 6	3
spic.chord	24.0	24.0 25.5	24.0 ­	­
spic.arc	30.0	27.0 32.5	30.0 ­	­
c'	6.4	5.4 6.7	6.4 7.6	7.2