Amphimonhystrella sinica, Uang & Sui, 2024

Uang, Mian & Sui, Xinxin, 2024, Description of Amphimonhystrella sinica sp. nov. and Cobbia zhangi sp. nov. of the family Xyalidae (Nematoda: Monhysterida) from the Yellow Sea, China, Zootaxa 5471 (3), pp. 343-354 : 345-348

Amphimonhystrella sinica sp. nov.

( Figures 1 and 2 )

Holotype and paratype material. Four males and two females were collected. Holotype male on slide JZW85-17 . Paratype 1 (male) on slide JZW12-11 , paratype 2 (male) on slide JZW89-1 , paratype 3 (male) on slide JZW73-7 , paratype 4 (female) on slide JZW50-28 and paratype 5 (female) on slide JZW50-37 .

Type locality and habitat. Subtidal sediment in the Jiaozhou Bay. Station JZW16: 36°06′ N, 120°15.3′E, water depth 22.5 m, muddy sediment.

Etymology. The species epithet refers to the country of origin, China.

Measurements. All measurement data are given in Table 1 .

Descriptions.

Males. Body small, cylindrical, tapering slightly towards both ends. Cuticle with fine striations. Inner labial sensilla papilliform, less visible; six outer labial setae, 3–4 µm long, occupying 50%–66% of head diameter, situated immediately anterior to four cephalic setae of the same length. Somatic setae absent. Amphidial fovea circular, 4 µm in diameter, occupying about 33% of corresponding body diameter, located relatively far from the anterior end of the body, 12–13 µm from the anterior end. Buccal cavity rhomboid-shaped, 5 µm deep and 3 µm wide, lightly cuticularized. Pharynx cylindrical, widening posteriorly but not forming true bulb. Cardia conical, 5–6 µm long, surrounded by intestine tissue. Nerve ring situated in the middle of pharynx, 44–53% of pharyngeal length. Secretory-excretory system not observed.

Reproductive system diorchic with two opposed, outstretched testes. Anterior testis situated to the left of intestine and posterior one situated to the right. Spicules slender, 1.4–1.5 cloacal body diameter in length, strongly curved at distal part, L-shaped with cephalated proximal end and hooked distal end. Gubernaculum tubular with two curved ventrally dorso-caudal apophyses. Tail slender, consisting of half conical proximal part and half cylindrical distal part. Some short caudal setae present in ventral side. Tail tip with two terminal setae, 5–7 µm long. Three caudal glands in tandem.

Females. Similar to males in most morphological characteristics except tail slightly longer (c’ = 8.4–8.9 versus 6.1–7.2). Reproductive system monodelphic with outstretched anterior ovary to the left of intestine; postvulvar sac present. Vulva situated just posterior to mid-body, 56% of body length from the anterior end.

Differential diagnosis and discussion. Amphimonhystrella sinica sp. nov. is characterized by buccal cavity rhomboid-shaped, amphidial fovea circular relatively far from anterior end of the body, slender L-shaped spicules with cephalated proximal end and hooked distal end, tubular gubernaculum with ventrally curved apophyses, slender conico-cylindrical tail with half cylindrical distal part.

Amphimonhystrella sinica sp. nov. is similar to A. tropica (b = 5.2–5.5; c = 6–7.1) and A. major Gagarin & Tu, 2021 (a = 31–38) in body size, but differs from A. tropica by buccal cavity rhomboid-shaped not divided into two sections as in the latter species; spicules L-shaped with hooked distal end (versus arcuated with tapered distal end) and gubernacular apophyses slender and strongly curved ventrally (versus triangular not curved in the latter species). The new species differs from A. major by buccal cavity small, conical, 5 μm deep, about 83% head diameter (versus large, elongated funnel, 12.5–13 μm deep, about 2 times head diameter), gubernacular apophyses ventrally hooked (versus straight in A. major ) and amphidial fovea farther posterior to buccal cavity (versus located at the level of buccal cavity base). In addition, the new species is distinguished from another species found in China, A. boucheri by the latter species possessing deep funnel shaped buccal cavity, shorter conico-cylindrical tail (c′ = 5.6–6.3) with two thirds conical anterior portion and a third cylindrical posterior portion, males with relatively short L-shaped spicules (sp./a.b.d. = 0.7 versus 1.4–1.5) and tubular gubernaculum with small triangular apophysis. The new species is also distinguished from A. bullacauda easily by male reproductive system paired testes (versus single testis), tail shorter (c = 5.3–7.1 versus 6.7–7.4), tail end cylindrical (versus tail enlarged in terminal portion). The differences among A. sinica sp. nov. and its congeners can be inferred from the key below.

Figures

FIGURE 1. Drawing of Amphimonhystrella sinica sp. nov. (A) anterior end of male; (B) entire male; (C) entire female; (D) anterior end of female; (E) posterior end of male; (F) spicule and gubernaculum. Scale bars: A, D, F 10 μm; B, C 30 μm; E 20 μm.

FIGURE 2. Microscopic images of Amphimonhystrella sinica sp. nov. (A) anterior end of holotype, showing anterior sensory setae and buccal cavity; (B) anterior end of female, showing buccal cavity and amphidial fovea (arrow); (C) posterior portion of holotype, showing spicules, gubernaculum; (D) high magnification of spicules and gubernaculum. Scale bars: A, B 5 μm; C, D 10 μm.