Ingenia major Yanwei, Wen & Mengna, 2024, sp. nov.

Ingenia major sp. nov. (Figures 1–2, Table 1) Type material. One male was measured and studied. Holotype: ♂ 1 on slide 19YD1-1-13. Type locality and habitat. Specimens were obtained from intertidal sandy sediment at Yantai coast, Shandong Province, China, 37º47´N, 121º48 ΄E. Etymology. Species epithet major refers to the large body size. Description. Male. Body columnar, very long and thick. Cuticle striated. Anterior sensilla arranged in two separate circles: six inner labial setae in one circle, six outer labial setae and four cephalic setae arranged in another circle. Outer labial setae approximately equal to head diameter in length, and each setae divided into four segments, with apical end swollen. Buccal cavity large and barrel-shaped, with one large dorsal tooth, two small subventral teeth. Amphidial fovea unispiral-shaped, 20% of corresponding body diameter (c.b.d.) in diameter, and 32 µm from anterior end. Pharynx cylindrical and slight swollen proximally. Nerve ring located slightly anterior to 1/3 pharynx length (31% of pharynx length). Secretory-excretory system not observed. Reproductive system with single and outstretched testis, located on the right of intestine. Spicules thin and almost straight, 1.2 times of cloacal body diameter in length, with a pair of ventro-laterally directed teeth (8 µm in length) hooked distally. Gubernaculum kidney-shaped with triangular cuticularized projection, precloacal supplements absent. Tail conical, 2.6 times of cloacal body diameter, gradually tapering with swollen terminus. Three caudal glands in a line. Caudal setae absent. Females. Not found. Differentiation diagnosis and discussion. Ingenia major sp. nov. is characterized by body large and thick, six outer labial setae articulated, amphidial fovea small and unispiral, buccal cavity large and barrel-shaped with three teeth, spicules thin and almost straight with a pair of ventro-laterally directed teeth hooked distally, gubernaculum kidney-shaped with triangular cuticularized projection, tail conical with swollen terminus. Until the moment specimens of Ingenia are rare and here we compare the only specimen, a female, of Ingenia mirabilis with the only specimen, in this case a single male, of the new species. Ingenia major sp. nov. is similar to I. mirabilis in the articulated outer labial setae, large and barrel-shaped buccal cavity with three teeth, slender and proximal swollen pharynx. The new species significantly differs from I. mirabilis in longer body size (3470 µm vs. 1700 µm), slender body shape (36 µm vs. 52 µm in maximum body diameter), shorter inner labial setae length (11 µm vs. 18 µm), shorter outer labial setae length (29 µm vs. 45–50 µm), more sections of outer labial setae (four parts vs. two or three parts), smaller amphidial fovea size (6 µm vs. 10 µm in diameter), amphidial fovea located closer to the anterior end of the body (32 µm, at level of buccal cavity vs. 60 µm from anterior end, posterior to buccal cavity), higher de Man “a” ratio (96.4 vs. 33) and de Man “c” ratio (42.3 vs. 18.5), as well as different tail shape (conical vs. conico-cylindrical).