Amynthas biorbis Tsai CF and Shen, 2010

Tsai, Chu-Fa, Shen, Huei-Ping & Tsai, Su-Chen, 2010, Four new species of Amynthas earthworms (Oligochaeta: Megascolecidae) from the Central Mountain Range of southern Taiwan, Journal of Natural History 44 (21 - 22), pp. 1251-1267 : 1260-1262

Amynthas biorbis Tsai CF and Shen , sp. nov.

( Figure 3 )

Type material

Holotype. Clitellate (86 mm in length, dissected) collected 16 March 2000 near Hsinwu (elevation 412 m), Taitung County by C.F. Tsai, S.C. Tsai, H.P. Shen, S. T. Chang, H.S. Fang, H.P. Yang, and T. J. Lin (TESRI-O-H-33).

Paratypes. Two clitellates collected 16 March 2000 along Yenping Forest Road (elevation 1000 m) near Hongyeh Village , Taitung County by the same collectors of the holotype (TESRI-O-P-28) .

Other material

One clitellate (dissected) collected 15 March 2000 at Meishanko (elevation 1000 m) along Road 20, Kaohsiung County by the same collectors of the holotype (coll. no. 2000-15- Shen); one amputated clitellate (same collection data as holotype, coll. no. 2000-25-Shen) .

Diagnosis

Small earthworm; length (clitellates) 61–86 mm. Segments numbering 72–97. Setae 33–40 in VII, 41–48 in XX, and 8–12 between male pores. Spermathecal pores four pairs, buried deeply in intersegmental furrows of 5/6–8/9, 0.28–0.29 body circumference ventrally apart. Male pores 0.24–0.3 body circumference ventrally apart in XVIII, each on a round porophore about 0.3 mm in diameter with concave centre. A pair of large genital papillae in XVIII, each papilla round, about 0.5 mm in diameter, closely adjacent to the male porophore at the medio-posterior portion immediately posterior to the setal line. No genital papillae in the preclitellar region. Spermathecae four pairs in VI–IX. Seminal vesicles two pairs in XI and XII, each small, with a prominent and round or peach-shaped dorsal lobe. Prostate glands large, deeply divided into five or six lobes with follicular surface in XVI–XX. Prostatic duct U-shaped, proximal portion enlarged. A large accessory gland with folliculated patch extending longitudinally near the proximal end of the prostatic duct, corresponding to each external genital papilla.

Description

External characters. Total length (clitellates) 61–86 mm. Weight 0.31–0.67 g. Segments numbering 72–97. Clitellum XIV–XVI, setae and dorsal pores absent, 2.05–2.4 mm in length and 2.63–3.32 mm in width. Prostomium epilobous. Setal number 33–40 in VII, 41–48 in XX, and 8–12 between male pores in XVIII. First dorsal pore in 11/12. Spermathecal pores four pairs, each small, not easily detectable, buried deeply in intersegmental furrows of 5/6–8/9, distance between paired pores 0.28–0.29 body circumference ventrally apart. No genital papillae in the preclitellar region. Female pore single, mid-ventral in XIV.

Male pores paired on setal line in XVIII, 0.24–0.3 body circumference ventrally apart. Each pore on a round porophore about 0.3 mm in diameter with concave centre. A pair of genital papillae in XVIII, each papilla round, about 0.5 mm in diameter (larger than male porophore), closely adjacent to the male porophore at the medio-posterior portion immediately posterior to the setal line; both porophore and genital papilla surrounded by one or two skin folds ( Figure 3A ).

Preserved specimens pinkish brown on head and dorsum, light brown on ventrum, and dark pinkish brown on clitellum.

Internal characters. Septa 5/6–7/8 and 10/11–13/14 thick, 8/9/10 absent. Nephridial tufts thick on anterior faces of 5/6/7. Gizzard large, round in VIII–X. Intestine enlarged from XV. Intestinal caeca paired in XXVII, extending anteriorly to XXIII or XXIV, each simple, slightly folded, the end straight or bent dorsally ( Figure 3E ). Oesophageal hearts in XI–XIII.

Spermathecae four pairs in VI–IX, each with a conical or peach-shaped ampulla of 0.9–1.11 mm long and 0.45–0.68 mm wide, and a slender to stout spermathecal stalk of 0.45–0.79 mm that is about one-half to two-thirds of the ampullar length. Diverticulum with a small, oval-shaped seminal chamber and a slender stalk 0.35–0.75 mm in length, about the same length to spermathecal stalk ( Figure 3B ).

Holandry. Testes small or large, two pairs in ventrally joined sacs in X and XI. Vas efferens connected in XII on each side to form a vas deferens. Seminal vesicles two pairs in XI and XII, each small, with a prominent and round or peach-shaped dorsal lobe ( Figure 3C ). Prostate glands large, deeply divided into five or six lobes with follicular surface in XVI–XX. Prostatic duct U-shaped, in XVIII or XVII–XVIII, proximal portion enlarged. A large sessile accessory gland with folliculated patch extending longitudinally near the proximal end of the prostatic duct, corresponding to each external genital papilla ( Figure 3D ).

Etymology

The name biorbis is given to this species to indicate the large, paired genital papillae adjacent to the male porophores.

Remarks

Amynthas biorbis sp. nov. is endemic to the east and west slopes of the Central Mountain Range at elevations of 400–1000 m in southern Taiwan. It belongs to the diffringens (= corticis ) species-group of the genus Amynthas ( Sims and Easton 1972) , and is closely related to A. uvaglandularis which is found at elevations of 1800–2300 m in central Taiwan ( Tsai et al. 2004) and also at 1300–2300 m (this trip) in southern Taiwan. Amynthas biorbis differs from A. uvaglandularis by having no genital papilla in the preclitellar region, and only a pair of large and round papillae in XVIII located posterior to setal line and closely adjacent to male porophores ( Figure 3A ). Amynthas uvaglandularis has genital papillae in VIII, IX and XVIII, whose number and positions are highly variable ( Shen et al. 2003).

Amynthas biorbis is also fairly similar to A. corticis . However, the former is smaller, with a pair of large papillae medio-posterior to male pores and no genital papilla in the preclitellar region. These characters are consistent among the A. biorbis individuals and distinctly different from the variable papillae arrangements in the preclitellar and male pore regions of A. corticis ( Table 3). Gates (1959) and James et al. (2005) reported A. corticis (= A. diffringens ) specimens from Pingtung, southern Taiwan with fully developed reproductive organs showing no signs of male sterility ( Table 3). Nevertheless, these authors are not quite sure whether their specimens are indeed the so-called A. corticis or a form closely related to A. corticis . The second author of this study has examined the A. corticis specimens described by James et al. (2005), and we have also collected specimens fairly similar to A. corticis but with fully developed reproductive organs from southern Taiwan (unpublished data). More specimens and further study are needed to solve this question.

Figures

Figure 3. Amynthas biorbis sp. nov. Holotype (TESRI-O-H-33) (86 mm): (A) ventral view of male pore region (mp, male porophore; gp, genital papilla;); (B) dorsal view of right spermathecae (amp, ampulla; dv, diverticulum); (C) dorsal view of right seminal vesicles (sv) (dl, dorsal lobe); (D) dorsal view of right prostate gland (ac, accessory gland); (E) dorsal view of right caecum.