Holotype • One clitellate (L609_03_05), Cheng County, Longnan Prefecture, Gansu Province, China, 25 July 2025, leg. Hao Zhang and Mengyu Ren. Paratypes • Six clitellates: five specimens (L609_03_04, 06, 08, 10, 11) with the same data as the holotype; and one specimen (L609_19_01), Hui County, Longnan Prefecture, Gansu Province, China, 26 July 2025, leg. Congsheng Li and Ye Chen. All type and non-type specimens are deposited in C-HLU.

Big size. Brown when preserved in alcohol. Prostomium epilobous (Fig. 1A). Clitellum in XIV–XVI, annular, dorsal pore absent, setae absent. Setae perichaetine arrangement. First dorsal pore 12/13 (Fig. 1B). Spermathecal pores three pairs in 6/7–8/9, lateral, slit-like (Fig. 1D, L, N). Female pore medio-ventral in XIV, single (Fig. 1C). Male pores paired in XVIII (Fig. 1J, P–S). Genital markings present, two pairs of ventral papillae presetal on segments VII and VIII; one pair postsetal on segment VIII, closer to the ventral midline than anterior pairs (Fig. 1D, L, N). Gizzard in VIII–X (Fig. 1E). Paired intestinal caeca in XXVII, extending forward to segment XXIII, with 5 (rarely 6) secondary caeca, the ventral-most one being the longest (Fig. 1M, O). Spermathecae three pairs in VII–IX (Fig. 1G, K). Accessory glands clustered, sessile (Fig. 1H). Seminal vesicles in XI–XII, separate ventrally (Fig. 1I). A pair of prostate glands well-developed, in segments XVI–XXII, follicular, with a thin U-shaped prostatic duct (Fig. 1F).

External characters. Length 112–169 mm, diameter 6–8 mm, number of segments 67–107. In alcohol, anterior region darker brown dorsally, paling ventrally to yellowish-brown; posterior region palest, pale brownish-yellow; clitellum lightest, grayish-white. Prostomium epilobous. First dorsal pore 12/13. Clitellum annular in XIV–XVI, smooth, swollen, setae absent, dorsal pore absent. Setae perichaetine arrangement; setae number 64–77 at V, 74–88 at XII, 80–83 at XX, 16–18 between male pores, setal formula AA = 1.1–1.6AB, ZZ = 1.2–1.5YZ.

Spermathecal pores three pairs in 6/7–8/9, intersegmental, lateral, about 0.5 circumference ventrally apart. Opening a small labiform slit, with slightly glandular-swollen perimeter. Pre-clitellar genital markings present. Two papillae pairs presetal on VII and VIII, ventrolateral, small and circular, approximately 7.2 mm from ventral midline; one pair postsetal on VIII, ventral, slightly larger and elliptical, approximately 6.5 mm from ventral midline.

Male pores paired in XVIII, about 0.24 circumference ventrally apart, each pore opens upon a large tuberculum, with two or three extremely minute, circular papillae on their lateral sides. With male pores papillae closely arranged; when two, superposed, in figure-8 pattern; when three, arranged in triangle, one at each vertex. Female pore single, on mid-ventral line in XIV.

Internal characters. Septa 8/9–9/10 absent, 4/5–7/8 and 10/11–12/13 thickened and muscular, 13/14–15/16 thicker than those following. Dorsal blood vessel single, continuous onto pharynx; esophageal hearts four pairs in X–XIII, the first pair less developed than the others, and the posterior two pairs being thicker. Subspherical gizzard with equatorial constriction within VIII–X. Intestine enlarged from XV. Intestinal caeca complex, paired originating in XXVII and extending anteriorly to XXIII, dorsally with five (rarely six) secondary caeca, the ventral-most being the longest.

Testis sacs in X and XI, oval, separated ventro-medially. Seminal vesicles two pairs in XI and XII, well developed, both connected ventro-medially with a slim tube. Prostate gland paired in XVI–XXII, lobed, well developed, distal end of a small inverted U-shaped duct stout, in XVIII.

Spermathecae three pairs in VII–IX, well developed, big. Ampulla ovate, wrinkled, 3.50–4.30 mm long, 3.07–3.45 mm wide; ampulla ducts short and stout, 1.21–1.32 mm long, 0.67–0.89 mm wide. Diverticulum subequal to ampulla, stalk 1.56–2.29 mm long, receptacle 3.03–3.64 mm long. Receptacle full, fusiform (club-shaped, slightly enlarged medially), surface smooth. Accessory glands clustered, sessile, adherent to body wall.

The specific name of the species refers to the type locality in Longnan Prefecture, Gansu Province.

Northwest China (Gansu).

Forest.

A. longnanensis sp. nov. belongs to the A. sieboldi group within the species groups of Sims and Easton (1972). The new species is similar to A. pectiniferus (Michaelsen, 1931), which is distributed in southeastern China (Jiangsu, Zhejiang, Anhui, Jiangxi) (Xu and Xiao 2011). Both species share the epilobous prostomium, the first dorsal pore opening in 12/13, three pairs of spermathecal pores in 6/7–8/9, three pairs of papillae on VII–VIII (Chen 1959), and caeca complex with 5–6 pectinate branches. However, the new species is shorter in body length, primarily brown in color; with 2–3 papillae located laterally to the male pores, arranged in an “8”-shaped or triangular pattern, each positioned at the corners of the triangle; the spermathecal pores are lip-shaped slits. In contrast, A. pectiniferus is larger, with a deep purple or purplish-red dorsum and lateral sides; it bears 3–4 papillae laterally to the male pores arranged in a rectangular pattern, each at the corners of the rectangle; the spermathecal pores are rather large, cross-shaped slits (Xu and Xiao 2011). Internally, the accessory glands of the new species appear as wart-like protrusions without cord-like short ducts; the diverticula are similar in length to the spermathecae. In A. pectiniferus, the accessory glands possess cord-like short ducts, and the diverticula are longer than the spermathecae (Xu and Xiao 2011).

Furthermore, the new species is further distinguished from A. szechuanensis (Chen, 1931), A. leshanensis Sun, 2016, and A. daulis (Zhong & Ma, 1979). It is similar in body size to A. szechuanensis but larger than A. leshanensis and A. daulis. The first dorsal pore is located at 12/13 (vs. 11/12 in A. szechuanensis and A. leshanensis; 4/5 or 11/12–12/13 in A. daulis).

The new species possesses three pairs of pre-clitellar papillae in the spermathecal pore region, which are absent in the other three species. Post-clitellar papillae are present in all except A. leshanensis: 2–3 very small, round papillae lateral to the male pores in the new species; five small round papillae or a large horseshoe-shaped papilla irregularly arranged around the male pores in A. szechuanensis; and a pair posterior to the setae on XVII in A. daulis.

All four species have manicate intestinal caeca, but differ in structure: 5–6 long lobes, the longest ventral in the new species; 12–15 dorsally split, finger-like small sacs in A. szechuanensis; three finger-like sacs in A. leshanensis; and 4–7 dorsally arranged finger-like small sacs in A. daulis. Additionally, the diverticula are approximately as long as the spermathecal sacs in the new species, but shorter in the other three species (Table 3) (Chen 1959; Zhong and Ma 1979; Sun et al. 2016).

Holotype • One clitellate (L622_10_07), collected in Huazhou Park, Weinan Prefecture, Shaanxi Province, 2025-07-16, collected by Yufeng Zhang, Ye Chen and Mengyu Ren. The holotype is preserved in C-HLU.

Medium size. Brown when preserved in alcohol. Prostomium epilobous (Fig. 2A). Clitellum in XIV–XVI, annular, dorsal pore present, setae absent. Setae perichaetine arrangement. First dorsal pore on 13/14 (Fig. 2B). Spermathecal pores three pairs in 6/7–8/9, lateral, eye-like (Fig. 2D, N). Female pore medio-ventral in XIV, single (Fig. 2C). Male pores paired in XVIII (Fig. 2J, K). Genital markings present, two pairs of ventral papillae presetal on VII and VIII; one pair postsetal on VIII, closer to the ventral midline than anterior pairs (Fig. 2D, N). Gizzard in VIII–X (Fig. 2E). Paired intestinal caeca in XXVII, extending forward to segment XXIV, with 5 secondary caeca, ventral-most longest (Fig. 2L, M). Spermathecae three pairs in VII–IX (Fig. 2G, O). Accessory glands with cord-like short tubes (Fig. 2H). Seminal vesicles in XI–XII, separate ventrally (Fig. 2I). Prostate glands paired well-developed, in segments XV–XX, follicular, with thin U-shaped prostatic duct (Fig. 2F).

External characters. Length 107 mm, diameter 6 mm, number of segments 107. In alcohol, clitellum and preclitellar dorsum dark brown, postclitellar dorsum yellowish-brown, venter yellow. Prostomium epilobous. First dorsal pore on 13/14. Clitellum annular in XIV–XVI, smooth, swollen, dorsal pore present, setae absent. Setae perichaetine arrangement; setae number 55 at V, 69 at XII, 60 at XX, 12 between male pores, setal formula AA = 1.2AB, ZZ = 2.7YZ.

Spermathecal pores three pairs in 6/7–8/9, intersegmental, lateral, about 0.5 circumference ventrally apart. Eye-like, with slightly glandular-swollen perimeter. Pre-clitellar genital markings present, three pairs of papillae on VII and VIII, small and circular. Two pairs presetal on VII and VIII respectively, ventrolateral, approximately 3.9 mm from ventral midline; one pair postsetal on VIII, ventral, approximately 2.7 mm from ventral midline.

Male pores paired in XVIII, about 0.24 circumference ventrally apart, male pore field swollen. Male pores laterally covered by saccular skin fold. Longitudinal slit present medially in each male pore field, with tongue-shaped papilla protruding from slit. Female pore single, on mid-ventral line in XIV.

Internal characters. Septa 8/9–9/10 absent, 4/5–7/8 and 10/11–12/13 thickened and muscular, 13/14–15/16 thicker than following. Dorsal blood vessel single, continuous onto pharynx; esophageal hearts four pairs in X–XIII, first pair less developed than others. Gizzard fusiform in VIII–X, laterally constricted, centrally dilated. Intestine enlarged from XV. Intestinal caeca complex, manicate, paired originating in XXVII and extending anteriorly to XXIV, dorsally with five secondary caeca, the ventral-most longest, 2^nd and 5^th extremely short; 1^st, 3^rd and 4^th with undulate margins.

Testis sacs in X and XI, oval, separated ventro-medially. Seminal vesicles two pairs in XI and XII, well developed, both connected ventro-medially with slim tube. Prostate gland paired, lobed, well developed, left in XV–XX, right slightly posterior in XVI–XX. Distal end of small, inverted U-shaped duct stout, located in XVIII.

Spermathecae three pairs in VII–IX, well developed. Ampulla nearly elliptical, full, 2.2 mm long, 1.6 mm wide; ampulla ducts short, cylindrical, 1.0 mm long, 0.5 mm wide. Diverticulum longer than ampulla, stalk 1.9 mm long, v-shaped; receptacle slightly enlarged, clavate, 2.5 mm long, full, surface smooth. Accessory glands with cord-like short tubes.

The specific name refers to the type locality, Weinan Prefecture, Shaanxi Province, which located in the Guanzhong region of China.

China (Shaanxi).

Lawn.

The new subspecies closely resembles A. pectiniferus in body dimensions, epilobic prostomium, papillar arrangement (two pairs presetal on VII–VIII and one pair postsetal on VIII), and accessory glands bearing short cord-like tubes. It differs externally in its yellowish dorsal coloration (vs. dark purple or purplish red in A. pectiniferus) and in having the first dorsal pore at 13/14 (vs. 12/13). Both taxa possess three pairs of spermathecae in VII–IX with club-shaped, smooth diverticula exceeding the ampulla in length. However, the ampulla duct is approximately half the ampulla length in the new subspecies (ratio ~1:2), whereas it is subequal to the ampulla in A. pectiniferus (ratio ~1:1). Furthermore, the stalk is medially folded and V-shaped in the new subspecies, but naturally curved without folding in A. pectiniferus. The intestinal caeca of both taxa are complex, each with five branches originating in XXVII and extending anteriorly to XXIV. In A. p. guanzhongensis ssp. nov., the caeca are pinnate with complex folds: the 1^st, 3^rd and 4^th branches bear undulate margins, while the 2^nd and 5^th are extremely short. In contrast, the caeca of A. pectiniferus are digitate with smooth surfaces and even margins, with only the second branch shortened (Table 3).