Holotype. Clitellate (mature) specimen (52 mm in length, dissected) collected 28 April 2014 from roadside slopes and ditches around Dinghu (elevation 1664 m), Alishan, Chiayi by H.T. Fang (TESRI-O-H- 50) (voucher number: Ali032).

Paratypes. Four clitellates (same collection data as holotype, TESRI-O-P- 45).

One clitellate collected 16 August 2013 from roadside slopes and ditches around Dinghu (elevation 1664 m), Alishan, Chiayi by H.T. Fang (coll. no. 2013 – 8) (voucher number: Ali024); one clitellate collected 28 April 2014 from roadside ditches around a parking lot at south end of a hiking trail in Longyun Farm (elevation 1486 m), Jhuci, Chiayi by H.T. Fang (coll. no. 2014 – 8) (voucher number: Ali044).

Small earthworm; length (clitellates) 41 – 52 mm. Segments numbering 75 – 87. Setae 26 – 35 in VII, 31 – 34 in XX, and 6 – 8 between male pores. First dorsal pore in 11 / 12 or 12 / 13. Spermathecal pores four pairs in 5 / 6 – 8 / 9, 0.26 – 0.28 body circumference ventrally apart. Paired genital papillae usually present in presetal VIII. Male pores 0.27 body circumference ventrally apart in XVIII, each on the depressed centre of a round porophore about 0.3 mm in diameter. Two pairs of genital papillae medial to male porophores in postsetal XVII and presetal XIX. Spermathecae four pairs in VI – IX. Seminal vesicles large, two pairs in XI and XII. Prostate glands in XVI – XX, smooth, lobed. Prostatic duct S-shaped in XVIII, stouter toward distal end. Accessory glands absent.

External characters. Total length (clitellates) 41 – 52 mm. Weight 0.08 – 0.13 g. Segments numbering 75 – 87. Clitellum XIV – XVI, setae and dorsal pores absent, length 1.71 – 2.16 mm and width 1.78 – 1.98 mm. Prostomium epilobous. Setal number 26 – 35 in VII, 31 – 34 in XX, and 6 – 8 between male pores in XVIII. First dorsal pore in 11 / 12 or 12 / 13. Spermathecal pores four pairs in intersegmental furrows of 5 / 6 – 8 / 9, distance between paired pores 0.26 – 0.28 body circumference ventrally apart (Figure 5 a). Paired genital papillae usually present in presetal VIII or VIII – IX, about five intersetal distances apart, each papilla round, about 0.25 mm in diameter. Preclitellar papillae absent in one specimen. Female pore single, mid-ventral in XIV.

Male pores paired in XVIII, about 0.27 body circumference ventrally apart, each on the depressed centre of a round porophore about 0.3 mm in diameter (Figure 5 b). Two pairs of genital papillae medial to male porophores, one pair in postsetal XVII and the other in presetal XIX. Each papilla round, about 0.27 mm in diameter with concave centre. Papillae in presetal XIX absent in one specimen.

Preserved specimens light or greyish brown in colour.

Internal characters. Septa 5 / 6 – 7 / 8 and 10 / 11 – 13 / 14 thick, 8 / 9 / 10 absent. Nephridial tufts on anterior faces of 5 / 6 / 7. Gizzard large in VIII – X. Intestine enlarged from XVI. Intestinal caeca paired in XXVII, extending anteriorly to XXII, each simple with a round, white end. Oesophageal hearts in XI – XIII.

Spermathecae four pairs in VI – IX, varied in sizes and shapes (Figure 5 c). Each ampulla elongated oval-shaped, surface wrinkled, 0.60 – 1.00 mm long and 0.20 – 0.53 mm wide, with a stout spermathecal stalk of 0.30 – 0.52 mm in length. Diverticulum with a slender stalk of 0.30 – 0.45 mm in length and an iridescent, oval-shaped seminal chamber of 0.25 – 0.30 mm long. Accessory glands stalked, about 0.3 mm in total length, each corresponding to external genital papilla.

Holandry: testes large, oval, two pairs in ventrally joined sacs in X and XI. Seminal vesicles large, two pairs in XI and XII, occupying an entire segmental compartment. Prostate glands in XVI – XX (Figure 5 d), smooth, lobed. Prostatic duct S-shaped in XVIII, stouter toward distal end. Accessory glands absent.

GenBank accession numbers KU 232793 (Ali032, holotype), KU 232792 and KU 232794 (Ali024 and Ali044, respectively).

The name dinghuensis is given to this species with reference to its type locality at Dinghu, Alishan, Chiayi, southwestern Taiwan.

Amynthas dinghuensis is an octothecate earthworm belonging to the di ff ringens (= corticis) species-group (Sims and Easton 1972). Its genital papilla arrangement in the male pore area is most similar to Amynthas micronarius (Goto and Hatai 1898) from Japan when compared with other members of this group. However, A. dinghuensis has two pairs of papillae with one pair in postsetal XVII and the other in presetal XIX whereas the two pairs of papillae are in XVIII for A. micronarius. Also, A. micronarius is larger with body length 66 – 119 mm long and width 2.5 – 4.0 mm wide, and has less developed seminal vesicles and spermathecae without diverticula or with minute diverticula (Ohfuchi 1937).

The papilla arrangement in the male pore area of A. dinghuensis also looks similar to that of the peregrine Amynthas hupeiensis (Michaelsen 1895) and Amynthas tetrapapillatus Quan and Zhong, 1989 from Hainan Island, China. Both A. hupeiensis and A. tetrapapillatus are much larger, and have much higher setal number and paired genital papillae in the intersegmental furrows of 17 / 18 and 18 / 19. In addition, the former has three pairs of spermathecal pores in intersegmental furrows of 6 / 7 – 8 / 9 and very long diverticula (Chen 1933; Tsai 1964), and the latter has a pair of spermathecal pores on the dorsal side of the intersegmental furrow of 5 / 6. Therefore, A. dinghuensis is easily distinguishable from the two species.