Description of Amphimonhystrella sinica sp. nov. and Cobbia zhangi sp. nov. of the family Xyalidae (Nematoda: Monhysterida) from the Yellow Sea, China Author Uang, Mian College of Life Sciences, Liaocheng University, Liaocheng 252059, China Author Sui, Xinxin 0009-0001-9679-0697 College of Life Sciences, Liaocheng University, Liaocheng 252059, China 1215702465@qq.com text Zootaxa 2024 2024-06-19 5471 3 343 354 http://dx.doi.org/10.11646/zootaxa.5471.3.4 journal article 298692 10.11646/zootaxa.5471.3.4 4d1f58d2-1ccb-4b6f-9ec2-47c453583a82 1175-5326 12190148 E5A2FCFF-9066-4A30-AEE0-3510B6BD7B32 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 . TABLE 1. Individual measurements of Amphimonhystrella sinica sp. nov. (all measurements in µm except a, b, c, c′ and V%). Abbreviations: a, ratio of body length to maximum body diameter; b, ratio of body length to pharynx length; c, ratio of body length to tail length; c′, ratio of tail length to cloacal or anus body diameter; V%, position of vulva from anterior end expressed as a percentage of total body length; sp./a.b.d., the ratio of spicule length to anal body diameter; -, no data.

Holotype	Paratypes
Characters	M1	M2	M3	M4	F1	F2
Total body length	656	735	732	736	699	715
Maximum body diameter	19	20	20	19	22	23
Head diameter	6	6	6	6	6	6
Length of cephalic setae	4	3	4	4	3	4
Diameter of amphidial fovea	4	4	4	4	4	4
Pharynx length	121	138	135	135	133	137
Body diameter at pharyngeal base	19	19	19	18	21	20
Nerve ring from anterior end	63	60	71	61	66	70
Body diameter at nerve ring	17	16	17	16	17	16
Spicules length as arc	23	25	23	25	-	-
Length of gubernaculum	15	17	14	15	-	-
Body diameter at cloaca or anus	16	17	17	17	15	16
sp./a.b.d.	1.4	1.5	1.4	1.5	-	-
Tail length	107	122	117	104	133	134
Length of caudal setae	7	6	5	6	6	10
Vulva from anterior end	-	-	-	-	392	401
Body diameter at vulva	-	-	-	-	20	21
V%	-	-	56	56
a	34.5	36.8	36.6	38.7	31.8	31.1
b	5.4	5.3	5.4	5.5	5.3	5.2
c	6.1	6.0	6.3	7.1	5.3	5.3
c′	6.7	7.2	6.7	6.1	8.9	8.4

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. 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. 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.