Sphaerolaimus gracilis de Man, 1876

Sphaerolaimus gracilis de Man, 1876 View in CoL

Original description ( de Man, 1876: 179-181, fig. 47a- d, North Sea)

Other descriptions (de Man, 1922: 235-236, fig. 23a- b, North Sea. Stekhoven, 1935: 148, fig. 325a- c, North Sea. Stekhoven, 1942: 228, fig. 10a- c, Mediterranean Sea. Gerlarch, 1957: 172, fig. 121l- m, Brazil. Loof,

1961: 198-199, fig. 10a- b, North Sea, reexamination of type specimen. Gerlarch, 1965: 170, fig. 44a- c. Lorenzen, 1969: 209, fig. 10a- d, North Sea. Fadeeva, 1983: 1324-1326, fig. 2a- d, East Sea. Turpeenniemi, 1997: 72-81, fig. 4a- h, Baltic Sea)

Synonymised names ( Sphaerolaimus buetschlii Schulz, 1932 ; Sphaerolaimus demani Filipjev, 1922 ; Sphaerolaimus setosus Paramonov, 1927 )

Locality. The coast of Ilgwang-myeon , Gijang-gun , Busan: sub-tidal zone Southern part of East Sea, Korea ( 35°16 ʹ 0.0 ʺ N, 129°16 ʹ 50.0 ʺ E), at a depth of 16 m, in the clay sediment GoogleMaps .

Material. Three males ( MABIK NA00158050 , MABIK NA00158715 - MABIK NA00158716 ) collected by Jung-Ho Hong at the coast of Gijang on 30th April 2023, from Research Vessel Haeyanghwnangkyung 3 .

Measurements. See Table 2 for detailed measurements and morphometric ratios.

Description. Males ( Fig. 2 View Fig , Table 2). Body cylindrical, gradually tapering towards the tail end, about 1365-1520 μm long and 65-78 μm wide at the maximum body diameter. The cuticle finely striated with lateral alae measuring 10-15 μm in width, starting from the cervical region and extending to the base of the tail. Somatic setae in eight longitudinal rows, about 6-12 μm long in the cervical region, 5-7 μm long in the mid and tail part. The anterior end rounded with six small lips encircle the oral opening. Lip region rounded with six inner labial papillae. Six outer labial papillae and four cephalic setae (4-5 μm long) in one circle, anterior to buccal cavity. Subcephalic setae in eight groups situated, 2-3 setae (14-20 μm long) in each group. A series of longitudinal ridges located just in front of the buccal cavity. Buccal cavity barrel-shaped,

C

23-32 μm long, 20-25 μm wide composed in two parts, thick-walled anterior part and a sclerotized, thin-walled posterior part. Amphideal fovea circular, 8-11 μm in diameter or 24-28% of corresponding body diameter, located 23-33 μm from anterior apex. Pharynx nearly cylindrical, gradually expanding towards to the cardia, strongly muscular throughout its entire length. Cardia small, roundedconoid, surrounded by intestinal tissue. Nerve ring at 50- 54% of the pharynx length (140-181 μm long). Renette cell slightly behind the base of the pharynx, small oval shape, lateral to the intestine. Excretory pore near posterior to the nerve ring. Testes paired. Vas deferens well-developed. Spicules curved, 60-85 μm long along arch. Gubernaculum with dorsal-caudally directed apophysis 20-25 μm long. Precloacal supplements absent. Tail length 190-215 μm, conical anteriorly and cylindrical posterior- ly, pointed terminal end with three terminal setae (12-15 μm long). Three caudal glands open to the spinneret.

Remarks. Sphaerolaimus gracilis de Man, 1876 is characterized by the position of the amphid posterior to the buccal cavity; the length of spicules shorter than twice of anal body diameter; spicules not double jointed; spicules with consistent thickness; gubernaculum present; gubernaculum with straight dorsal apophyses ( Zograf et al., 2020). Based on the original description by de Man in 1876 from the brackish water of Walcheren Island, Netherlands, other descriptions made by many authors in the North Sea, Spitsbergen, the East Sea, and so on. Our specimens from the East Sea, Korea are similar to the description by Fadeeva in 1983 from the East Sea, but slightly smaller in body width (65-75 μm vs. 60-83 μm) and body length (1365-1520 μm vs. 1300-1700 μm). There is also a slight difference in spicules length (55-70 μm vs. 45-55 μm) and the apophysis length of the gubernaculum (15-20 μm vs. 13-14 μm).