Amphimonhystera pallida 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 : 16-19

Amphimonhystera pallida Tchesunov et Mokievsky sp. n.

( Figure 7 )

Type material: Holotype male 1 (ref # M­1/1), paratype male 2 (ref # M­1/2) and paratype female 1 (ref # M­1/8) mounted in glycerin on glass slides. Type specimens are deposited in the collection of the P. P. Shirshov Institute for Oceanology, Russian Academy of Sciences, Moscow.

Type locality: Arctic Ocean, area between Greenland and Svalbard, 79°8.2' N & 02°53.6' E, depth 5569 m (Molloy Deep), silt, 16 August, 2000.

Etymology: The species name reflects the pale colouration of the species in comparison with some other brownish Amphimonhystera species.

Morphometric data: Table 6 .

Description: Small nematodes with slender, near fusiform to cylindrical body. Cuticle thin, with fine transverse annulation. Subcuticular yellow­brownish granulation weakly developed (mainly in pre­amphidial and amphidial regions) in males or nearly absent in female. Pre­amphidial region more or less narrowed. Labial region slightly set off. Inner labial sensilla as poorly visible tiny papillae. Outer labial and cephalic sensilla united in one circle of ten setae of moderate length. Amphidial fovea large, longitudinally oval, with distinct unbroken cuticular edging and without a visible central spot. Somatic sensilla short, scarcely distributed laterally along the body; nearly absent in midgut region.

Buccal cavity small; cheilostoma hemispherical; esophastoma narrow, funnel shaped, with sclerotised walls. Esophagus slender, weakly muscular, gradually widening to the posterior end. Cardia small, triangular, internal. Midgut with distinct internal lumen and peritrophic membrane. At a short distance posterior to the cardia, the midgut shifted dorsally by a cell body which may be a pseudocoelomocyte or cell body of a rudimental renette cell. Anterior portion of the female branch situated left of the intestine, posterior portion right of the intestine. Uterus with two ripe eggs. Vulva as a small transversal slit. No vulval glands discernible. Anterior strait testis poorly discernible; posterior testis not visible at all. Two ejaculatory glands left of the vas deferens and intestine in the paratype male. Spicules short and slender, sharply bent in the middle, distally acute and proximally cephalated. No gubernaculum. Tail with a proximal conical and a distal slender cylindrical portion. Tail tip slightly inflated, with two or three terminal setae. No other somatic setae visible in tail region.

Diagnosis: Body pale, 655–740 µm long. Outer labial and cephalic setae 3.0–7.0 µm long. Amphidial fovea, 11–12 µm long; ratio length to width of the amphidial fovea 1.2– 1.4 µm; distance from cephalic apex to anterior rim of the amphidial fovea 14–21 µm. Spicules 24–26 µm long. Terminal caudal setae 4.0–9.0 µm long.

Differential diagnosis: Amphimonhystera palida sp. n. is similar to A. galea , A. marisalbi and A. molloyensis in body size. However, A. pallida differs from A. galea by having a much shorter cephalic setae length and shorter spicules; from A. marisalbi by a greater distance apex­amphidial fovea and longer terminal caudal setae; and from A. molloyensis by a greater distance apex­amphidial fovea.

Figures

FIGURE 7. Amphimonhystera pallida. (A) male 1 (holotype), entire; (B) male 1 (holotype), esophageal region; (C) male 1 (holotype), cephalic end; (D) male 2 (paratype), tail; (E) male 1 (holotype), spicule; (F) female 1 (paratype), entire; (G) female 1 (paratype), anterior end. Scale bars: (A), (B), (D) & (F) 100 µ m; (C), (E) & (G) 10 µ m.

Tables

TABLE 6. Morphometry of Amphimonhystera pallida

Specimen Label	Male 1 (holotype) ARK XVI, St 251 MD 317, 1–2 cm, 63 µm, 1/ 21	Male 2 (paratype) ARK XVI, St 251 MD 322, 1–2 cm, 63µm, 1/ 58	Female 1 (paratype) ARK XVII, St 125, B 0–1 cm, 125 µm, 1/42
Character L	655	735	740
a	32.7	35.0	24.8
b c	5.0 8.3	5.5 8.2	5.5 8.3
V (%) b.diam.c.s.	­ 5.0	­ 5.0	75.8% 7.5
b.diam.am.	11	13	12
b.diam.n.r. b.diam.c.	16 17	17 20	18 23
diam.midb. a.d..	20 15	21 15	30 17
c.s. c.s. (%)	3 0.60	7 1.40	7 0.93
am.w.	8	10	?
am.l. am.w. (%)	11 73	12 77	12?
am.l./am.w. dis.am.	1.4 14	1.2 14	? 21
st.w.	2.0	2	3.5
st.l. spic. chord	2.0 15	2.0 20	2.5 ­
spic. arc	24	26	­
c' dist. tail portion (%)	5.3 27	5.9 24	5.2 28
termin s.l.	4	5	9