Amynthas bilineatus Tsai and Shen, 2007

Tsai, Chu-Fa, Shen, Huei-Ping, Tsai, Su-Chen & Lee, Hsun-Huang, 2007, Four new species of terrestrial earthworms belonging to the genus Amynthas (Megascolecidae: Oligochaeta) from Taiwan with discussion on speculative synonyms and species delimitation in oligochaete taxonomy, Journal of Natural History 41 (5 - 8), pp. 357-379 : 366-368

Amynthas bilineatus Tsai and Shen , sp. nov.

( Figure 3 )

Type material

Holotype: a clitellate (mature) specimen (dissected) collected 14 February 2000 from hill slope along Dongyan Creek (elevation 1000 m), Jen-ai, Nantou County by C. F. Tsai, S. C. Tsai, H. P. Shen, T. J. Lin, and H. P. Chen (coll. no. 2000-3-Shen) . Paratypes: seven clitellates (three dissected) and three immature specimens (same collection data as holotype) .

Diagnosis

Medium earthworm; length (clitellates) 96–153 mm, segments numbering 89–104. Setal number 44–52 in VII, 52–56 in XX, eight between male pores. Spermathecal pores absent. Male pores 0.23–0.26 circumferences ventrally apart, each on a round or oval porophore surrounded by three or four circular folds. Genital papillae two on each segment on midventrum of VI–IX, arranged in two parallel longitudinal rows; each papilla round with a concave centre, presetal, adjacent to setal line. Also, genital papillae two to absent in XIX; if present, presetal, medial to male pore. Spermathecae absent. Seminal vesicles and prostate glands small, vestigial. Accessory glands sessile or stalked in the preclitellar region and stalked in the postclitellar region. Parthenogenetic.

External characters

Holotype 153 mm in length, 2.78 g in weight, clitellum width 5.3 mm, clitellum length 4.6 mm. Paratypes 96–118 mm in length, 0.82–1.23 g in weight, clitellum width 3.49– 4.18 mm, clitellum length 2.60–3.15 mm. Prostomium epilobous. Segments numbering 89–104. First dorsal pore 11/12. Number of incomplete annulets (secondary segmentation) two or three per segment in VI –XIII, XVII, and XVIII. Setal number 44–52 in VII, 52–56 in XX, eight between male pores in XVIII. Clitellum XIV–XVI, smooth, setae absent, dorsal pores absent, dark brown in colour with lighter anterior and posterior edges .

Spermathecal pores absent. Genital papillae presetal, closely paired in two parallel and longitudinal rows on mid-ventrum of VI – IX ( Figure 3A ) with numbers variable among specimens and segments. For eight mature type specimens examined, in VI one on right for two specimens , one on left for two specimens, paired for four specimens; in VII one on right for one specimen , paired for seven specimens; in VIII one on left for one specimen , paired for seven specimens; in IX paired for eight specimens ; in X paired for one specimen. Each papilla round, centre concave, 0.25–0.5 mm in diameter, adjacent to setal line. Female pore single, medio-ventral in XIV.

Male pores paired in XVIII, latero-ventral, distance between the pores 0.23–0.26 circumferences apart, and each pore minute, superficial, on a round or transversely oval porophore surrounded by three or four circular folds ( Figure 3B, C ). Genital papillae in XIX, presetal, each slightly medial to male pore ( Figure 3C ): for eight specimens examined, one pair for two specimens, one on left for two specimens, one on right for two specimens, absent for two specimens. The structure of the papillae similar to those in the preclitellar region.

Preserved specimens tinted pink in colour in the preclitellar region, light brown in the postclitellar region, and dark brown around clitellum.

Internal characters

Septa 8/9/10 absent, 5/6–7/8 and 10/11–13/14 thickened. Gizzard round in IX and X. Intestine enlarged from XVI. Intestinal caeca paired in XXVII, each simple, short, surface slightly wrinkled, extending anteriorly to full XXV or to two-thirds of XXIV ( Figure 3H ). Oesophageal hearts XI–XIII, the second and third hearts enlarged.

Spermathecae absent. Accessory glands corresponding to external genital papillae in the preclitellar region; each round, nearly sessile or with stalk to 0.26 mm in length ( Figure 3D ).

Holandry: sperm sacs paired in X and XI, each small and round. Seminal vesicles paired in XI and XII, small, follicular, surface slightly wrinkled, yellow in colour, each with a small oval dorsal lobe ( Figure 3E ). Prostate glands paired in XVIII, wrinkled, extending to XVII and XIX. Prostatic duct U-shaped, occupying two segments XVII and XVIII, distal end enlarged ( Figure 3F, G ). Accessory glands in XIX corresponding to external genital papillae, each slightly divided into two or three round lobes with stalks 0.24–0.31 mm in length ( Figure 3G ).

Etymology

The name bilineatus (bi 5two, lineatus 5lines) is given to this species with reference to its unique arrangement of two longitudinal lines (rows) of genital papillae on mid-ventrum of the spermathecal region.

Remarks

Amynthas bilineatus sp. nov. is athecate (A morph) and closely related to athecate Amynthas hohuanmontis ( Tsai et al., 2002) of central Taiwan and A. sheni of Hong Kong ( Chen 1935) and to nearly athecate A. chilanensis of northeastern Taiwan. Amynthas bilineatus has paired, longitudinal series of ventral genital papillae in VI–IX ( Figure 3A ) that are easily distinguishable from a single pair in VIII for sheni , and absent for chilanensis and hohuanmontis . Also, bilineatus has a pair of ventral genital papillae in XIX and absent in XVIII, differing from sheni , chilanensis , and hohuanmontis that have no genital papilla in XIX but in XVIII. The above four athecate species are closely related and belong to the sheni species-subgroup ( Tsai et al. 2002) of the illotus species-group ( Easton 1981) within the genus Amynthas Kinberg ( Sims and Easton, 1972) . They apparently evolved from a common ancestor as a result of allopatric speciation.

Figures

Figure 3. Amynthas bilineatus sp. nov. (A) Ventral view of preclitellar region (gp, genital papilla) of holotype; (B) ventral view of male pore (mp) region of holotype; (C) ventral view of male pore region of a 113-mm specimen (coll. no. 2000-3-Shen); (D) dorsal view of preclitellar accessory glands (ag) of holotype; (E) dorsal view of right sperm sacs (ss) and seminal vesicles (sv) of holotype (dl, dorsal lobe); (F) dorsal view of right prostate gland of holotype; (G) dorsal view of right prostate gland and accessory gland of a 113-mm specimen (coll. no. 2000-3- Shen); (H) dorsal view of right caecum of holotype.