Amynthas libratus 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 : 1256-1260

Amynthas libratus Tsai CF and Shen , sp. nov.

( Figure 2 )

Type material

Holotype. Clitellate (72 mm in length, dissected) collected 16 March 2000 along the Yenping Forest Road (elevation 1000 m) near Hongyeh , 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-32).

Paratypes. Three clitellates (same collection data as holotype, TESRI-O-P-27).

Diagnosis

Small earthworm; length (clitellates) 55–72 mm. Segments numbering 62–71. Setae 32–38 in VII, 34–41 in XX, and 9–11 between male pores. First dorsal pore in 5/6. Spermathecal pores four pairs in 5/6–8/9, 0.27–0.28 body circumference ventrally apart. Male pores 0.24–0.27 body circumference ventrally apart in XVIII, each on a round porophore surrounded by one to three shallow skin folds. Genital papillae tiny, in horizontal rows, one presetal with or without one postsetal, closely along the setal lines in VII–IX, XVII, XIX and occasionally XX. In addition, horizontal rows of smaller genital papillae closely along the intersegmental furrows, one anterior and one posterior to each of 17/18, 18/19 and occasionally 19/20. No genital papillae in the vicinity of the male pores. No presetal or postsetal papillae in XVIII. Spermathecae four pairs in VI–IX. Seminal vesicles two pairs in XI and XII, large, occupying one and a half segments. Prostate glands large, lobed with follicular surface in XVII–XX. Prostatic duct short, C-shaped or U-shaped. Accessory glands corresponding to external genital papillae in both preclitellar and postclitellar regions, each small with a round head and a slender stalk.

Description

External characters. Total length (clitellates) 55–72 mm. Weight 0.22–0.36 g. Segments numbering 62–71. Clitellum XIV–XVI, length 2.6–2.64 mm and width 2.31–3.03 mm. Prostomium epilobous. Setal number 32–38 in VII, 34–41 in XX, and 9–11 between male pores in XVIII. First dorsal pore in 5/6. Spermathecal pores four pairs, each small, oval in intersegmental furrows of 5/6–8/9; distance between paired pores 0.27–0.28 body circumference ventrally apart. Genital papillae tiny, round, tubercle-like, arranged in horizontal rows, one presetal and/or postsetal, closely along the setal lines in VII–IX ( Figure 2A ). The number of presetal papillae 0–5 in VII, 0–15 in VIII and 4–14 in IX; number of postsetal papillae 0–4 in VII, 9–15 in VIII and 5–15 in IX. No papillae in vicinity of the spermathecal pores and along intersegmental furrows. Female pore single, mid-ventral in XIV.

Male pores paired in XVIII, 0.24–0.27 body circumference ventrally apart. Each pore on a round porophore surrounded by one to three shallow skin folds. No genital papillae in the vicinity of the male pores. Genital papillae in horizontal rows closely along the setal lines in XVII, XIX and occasionally XX, similar to those in the spermathecal region. In addition, horizontal rows of smaller genital papillae closely along the intersegmental furrows, one anterior and one posterior to each of 17/18, 18/19 and occasionally 19/20 ( Figure 2B ). The number of presetal papillae 0– 11 in XVII and 0–14 in XIX; number of postsetal papillae 0–10 in XVII, 5–12 in XIX and 0–7 in XX. Total number (prefurrow and postfurrow papillae combined) 19–34 in 17/18, 23– 39 in 18/19 and 0–22 in 19/20. No presetal or postsetal papillae in XVIII.

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

Internal characters. Septa 6/7/8 and 11/12/13 thick, 8/9/10 missing. Nephridial tufts thick on anterior faces of 5/6/7. Gizzard large in VIII–X, rectangular shape, white in colour. Intestine enlarged from XV. Intestinal caeca paired in XXVII, extending anteriorly to XXIII or XXIV, each simple, slender, distal end either straight or bent dorsally ( Figure 2F ). Oesophageal hearts in XI–XIII.

Spermathecae four pairs in VI–IX, each with a round or oval-shaped ampulla 1.17– 1.58 mm long and 0.59–1.12 mm wide, and a slender spermathecal stalk 0.19–0.49 mm in length. Diverticulum with a small, oval-shaped seminal chamber and a slender stalk 0.59–0.65 mm in length, that is longer than the spermathecal stalk ( Figure 2C ).

Holandry. Testes small, two pairs in ventrally joined sacs in X and XI. Seminal vesicles large, two pairs in XI and XII, folliculated with a round dorsal lobe, occupying one and a half segments ( Figure 2D ). Prostate glands large, lobed with follicular surface in XVII–XX. Prostatic duct short, C- or U-shaped ( Figure 2E ).

Accessory glands corresponding to external genital papillae in both preclitellar and postclitellar regions. Each small with a round head 0.13–0.31 mm long and a slender stalk 0.35–1.25 mm in length ( Figure 2C,E ).

Etymology

The name libratus is given to this species with reference to the “horizontal line” in the arrangement of its genital papillae.

Remarks

Amynthas libratus sp. nov. is found on the east slope of the Central Mountain Range at elevations around 1000 m in southern Taiwan. It is an octothecate earthworm belonging to the diffringens (= corticis ) species-group of the genus Amynthas ( Sims and Easton 1972) , and closely related to A. pavimentus sp. nov. from elevations above 2000 m. A. libratus is distinguishable from A. pavimentus in the arrangement of genital papillae: the papillae of A. libratus are arranged in a single horizontal row at one side or both sides of setal lines or intersegmental furrows and no papilla around male pores ( Figure 2A,B ), whereas the genital papillae of A. pavimentus are patched between setal lines and intersegmental furrows, and often a few papillae are near the male pores ( Figure 1A,B ). The arrangement of genital papillae along setal lines and intersegmental furrows of A. libratus is fairly similar to that of the quadrithecate Amynthas kinfumontis (Chen, 1946) of China.

Figures

Figure 1. Amynthas pavimentus sp. nov. Holotype (TESRI-O-H-31) (121 mm): (A) ventral view of spermathecal pore region (gp, genital papilla; sp, spermathecal pore); (B) ventral view of male pore region (mp, male porophore); (C) dorsal view of right spermathecae (amp, ampulla; dv, diverticulum; ac, accessory gland); (D) dorsal view of right seminal vesicles (sv) (dl, dorsal lobe); (E) dorsal view of right prostate gland; (F) dorsal view of right caecum.

Figure 2. Amynthas libratus sp. nov. Holotype (TESRI-O-H-32) (72 mm): (A) ventral view of spermathecal pore region (gp, genital papilla; sp, spermathecal pore); (B) ventral view of male pore region (mp, male porophore); (C) dorsal view of right spermathecae (amp, ampulla; dv, diverticulum; ac, accessory gland); (D) dorsal view of right seminal vesicles (sv) (dl, dorsal lobe); (E) dorsal view of right prostate gland; (F) dorsal view of right caecum.