Amynthas fuscus Qiu & Sun, 2012

Sun, Jing, Jiang, Ji-Bao & Qiu, Jiang-Ping, 2012, Four new species of the Amynthas corticis-group (Oligochaeta: Megascolecidae) from Hainan Island, China, Zootaxa 3458, pp. 149-158 : 152-153

Amynthas fuscus Qiu & Sun , sp. nov.

( Fig. 1C, D)

Material. Holotype: One clitellate (C-HN012-01A) specimen, China, Hainan Province, Mt. Jianfeng (18°43.26’N, 108°53.56’E), 900 m. elevation, litter under Quercus near road, 4 Jun. 2006, J. P. Qiu, J. X. Li and W. X. Zhang coll. Paratypes: Four clitellates (C-HN012-01B): Same data as for holotype. Seven clitellates (C-HN011-01A), China, Hainan Province, Mt. Jianfeng (18°43.32’N, 108°53.33’E), 860 m. elevation, black sandy soil in shrubbery beside road, 4 Jun. 2006, J. X. Li and W. X. Zhang coll. Two clitellates (C-HN023-08), China, Hainan Province, Mt. Diaoluo (18°43.39’N, 109°51.55’E), 930 m. elevation, yellow soil under herbaceous vegetation beside road, 6 Jun. 2006, J. P. Qiu, J. X. Li and M. B. Bouché coll. Other material: Five aclitellates (C-HN011-01B), China, Hainan Province, Mt. Jianfeng (18°43.32’N, 108°53.33’E), 860 m. elevation, black sandy soil in shrubbery beside road, 4 Jun. 2006, J. X. Li and W. X. Zhang coll.

Etymology. This species is named after its brown pigment.

Diagnosis. Bigger-sized Amynthas earthworms; dark brown on dorsum and light brown on ventrum; four pairs of spermathecal pores in 5/6–8/9, 0.33 body circumference ventrally apart; Male pores 0.33 body circumference ventrally apart, each on the centre of a raised elliptical glandular flat top, conical, surrounded by a folded pad; diverticulum shorter than main spermathecal axis by 0.33, slender and coiled, terminal 0.25 dilated into elongated ovoid seminal chamber.

Description. External characters. Preserved specimens dark brown on dorsum, light brown on ventrum, unclear mid-dorsal line, no secondary annulations. Dimensions 95–149mm by 4–5mm at clitellum, segments 93–96; body cylindrical in cross-section, gradually tapered towards head and tail. Prostomium ½ epilobous. Setae numbering 30–34 at III, 28–36 at V, 32–40 at VIII, 42–50 at XX, 36–50 at XXV; 8–10 between male pores; 12–16/ VI, 13–16/VII, 13–16/VIII between spermathecal pores, setal formula AA=1–1.3AB, ZZ=1.3–2ZY. Clitellum annular 1/8XIV–7/8XVI, brown, swollen, setae and dorsal pore invisible.

First dorsal pore 11/12 or 12/13. Four pairs of spermathecal pores in 5/6–8/9, eye-like, 0.33 circumference ventrally apart. Male pores paired in XVIII, 0.33 body circumference ventrally apart; each on the centre of a raised elliptical glandular flat top, conical, surrounded by a folded pad. Genital markings not visible externally ( Fig. 1C). Female pore single, mid-ventral in XIV.

Internal characters. Septa 5/6–6/7 thick and muscular, 7/8 and 10/11–12/13 slightly thickened, 8/9–9/10 absent. Dorsal blood vessel single, continuous onto pharynx; esophageal hearts enlarged in X–XIII. Gizzard in VIII–X, ball-shaped; intestine enlarged gradually from XV and distinctly from XXI; intestinal caeca simple, originating in XXVII and extending forward to XXIV, surface smooth, finger-shaped sac with two slight incisions on terminal dorsal margin and one on ventral margin.

Ovaries in XIII. Spermathecae paired in VI–IX, about 3.2mm long; ampulla irregularly heart-shaped, gradually slender duct as long as 0.5 ampulla; diverticulum shorter than main spermathecal axis by 0.33, slender and coiled, terminal 0.25 dilated into elongated ovoid seminal chamber; no nephridia on spermathecal ducts ( Fig. 1D). One dissected specimen has a degenerated spermatheca in the left of VI, without ampulla and its duct. Male sexual system holandric, testis sacs two pairs, ventral in X, XI, connected on ventrum between left and right; seminal vesicles paired in each of XI and XII, developed, connected on ventrum between left and right; prostates developed, in XVII–XX, coarsely lobate with 3–4 major lobes, prostatic duct inverted u-shaped, distal end stouter. No accessory glands observed.

Remarks. Amynthas fuscus sp. nov. from Hainan Island belongs to the corticis -group in Sims and Easton (1972). It is closely related to Amynthas homosetus ( Chen, 1938) from China, Amynthas baemsagolensis Hong and James, 2001 from Korea and Amynthas sangumburi Hong and Kim, 2002 from Korea. These four species share a unique character combination in having no genital papillae either around the male pore region or the spermathecal pore region, having 4 pairs of spermathecal pores intersegmental in 5/6–8/9, simple intestinal caeca and developed prostates. Table 1 gives details of the differences among these species.

Amynthas fuscus sp. nov. is easily distinguishable from A. homosetus ( Chen, 1938) by the characters of the clitellum, male pores, distance between spermathecal pores transversely, and body pigment. As for the new species, the clitellum occupies 1/8XIV–7/8XVI with invisible setae, and the spermathecal and male pores are about 0.33 body circumference ventrally apart. While, in Amynthas homosetus , the clitellum is longer, occupying XIV–XVI with a few barely visible setal pits ventrally on XVI, and the spermathecal and male pores are about 0.25 body circumference ventrally apart. Otherwise, the diameter of the male pore glandular region in Amynthas fuscus was smaller than that in Amynthas homosetus .

Differences between Amynthas fuscus and Amynthas baemsagolensis are primarily in the body size, locations of clitellum and porophores of male pores. The new species has a smaller body size, clitellum extending less than three segments, male pores on the centre of a raised elliptical glandular flat top with a folded pad, but not on domed circular to oval porophores with 4–6 furrows.

Compared with Amynthas sangumburi , the present species has a bigger body size, more setae between male pores, smaller porophores of male pores, clitellum not regularly occupying XIV–XVI, and the stalk and seminal chamber of the diverticulum has a clear boundary, not widening gradually.

This new species is much more similar to Amynthas fornicatus (Gates, 1935) with respect to body size, the porophore of male pores, 4 pairs of spermathecal pores intersegmental in 5/6–8/9, same transverse distance between male pores and spermathecal pores, and the shape of spermathecae. However, A. fuscus sp. nov. has a rare clitellum situation which occupies 1/8XIV–7/8XVI, and has a papilla at the anterior edge of VI–IX which has been mentioned in Amynthas fornicatus ( Chen, 1936) . Another difference is that the diverticulum of A. fuscus sp. nov. is shorter than that of A. fornicatus ( Table 1).