Amynthas bimontis Shen, 2013

Shen, Huei-Ping, Chang, Chih-Han & Chih, Wen-Jay, 2013, Five new earthworm species of the genera Amynthas and Metaphire (Megascolecidae: Oligochaeta) from Matsu, Taiwan, Journal of Natural History (J. Nat. Hist.) 48 (9 - 10), pp. 495-522 : 499-501

Amynthas bimontis Shen , sp. nov.

( Figure 3 )

Type material

Holotype. Clitellate (48 mm in length, dissected) collected 26 June 2012 along the road between Chinbi Village and Bishan Lookout (elevation 210 m), Beigan by H.P. Chen and W.J. Chih (TESRI-O-H-38) (voucher number: MTS 105).

Paratype. One clitellate (same collection data as holotype, TESRI-O-P-33).

Diagnosis

Small earthworm; length (clitellates) 48 mm. Segments numbering 101. Setae 32–34 in VII, 30–34 in XX, and 5–6 between male pores. Clitellum XIV–XVI, with setae on the ventral side. First dorsal pore in 12/13. Spermathecal pores small, two pairs in 5/6/7, 0.29–0.3 body circumference ventrally apart. Male pores inconspicuous, 0.18–0.19 body circumference ventrally apart in XVIII, each on a round porophore 0.3–0.35 mm in diameter with depressed centre. Two small genital papillae lateral to each male porophore: one anterolateral and the other posterolateral. Genital papillae absent in the preclitellar region. Spermathecae two pairs in VI and VII. Seminal vesicles two pairs in XI and XII, small, vestigial, occupying half to two-thirds of segmental compartment. Prostate glands large in XVI–XXI or XVI–XXII. Prostatic duct long, S-shaped or U-shaped. Accessory glands large, sessile, amorphous, corresponding to external genital papillae.

Description

External characters. Total length (clitellates) 48 mm. Weight about 0.05 g. Segments numbering 101. Clitellum XIV–XVI, with setae on the ventral side, number 2 in XIV, 4 in XV and 4 in XVI, dorsal pores absent, length 1.23–1.61 mm and width 1.41–1.51 mm. Prostomium epilobous. Setal number 32–34 in VII, 30–34 in XX, and 5–6 between male pores in XVIII. First dorsal pore in 12/13. Spermathecal pores small, two pairs in intersegmental furrows of 5/6/7; distance between paired pores 0.29–0.3 body circumference ventrally apart ( Figure 3A ). Genital papillae absent in the preclitellar region. Female pore single, mid-ventral in XIV.

Male pores paired in XVIII, each inconspicuous on a round porophore 0.3–0.35 mm in diameter with depressed centre, 0.18–0.19 body circumference ventrally apart. Two small genital papillae lateral to each male porophore: one anterolateral and the other posterolateral ( Figure 3B ).

Preserved specimens greyish brown in colour.

Internal characters. Septa 5/6–7/8 and 10/11–13/14 thick, 8/9/10 missing. 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 XXIV–XXV, each short, simple. Oesophageal hearts in XI–XIII.

Spermathecae two pairs in VI and VII (quadrithecate). Each ampulla wrinkled, elongated oval-shaped, 0.75–0.98 mm long and 0.4–0.6 mm wide, with a slender spermathecal stalk 0.35–0.37 mm in length. Diverticulum long, tubular, 0.7–1.2 mm in length ( Figure 3C ). Accessory glands absent in the preclitellar region.

Holandry: testes small, oval, two pairs in ventrally joined sacs in X and XI. Seminal vesicles small, vestigial, two pairs in XI and XII, anterior pair occupying half to two-thirds of segmental compartment while posterior pair about half of the segmental compartment. Prostate glands large in XVI–XXI or XVI–XXII, wrinkled and lobed. Prostatic duct long, S-shaped or U-shaped in XVIII or XVIII–XIX ( Figure 3D, E ). Accessory glands large, sessile, amorphous, anterior gland in XVII–XVIII and posterior gland in XIX–XX, corresponding to external genital papillae.

DNA barcodes

GenBank accession number KC897062 (MTS 105, holotype) .

Etymology

The name bimontis is given to this species with reference to its type locality (elevation 210 m) near Mount Bi in Beigan , Matsu .

Remarks

Amynthas bimontis sp. nov. is a small earthworm only found on the island of Beigan. It is quadrithecate with two pairs of spermathecal pores in intersegmental furrows of 5/6/7, and so belongs to the morrisi species-group of the genus Amynthas ( Sims and Easton 1972) . Among the species of the morrisi -group listed by Sims and Easton (1972), Amynthas koreanus (Kobayashi, 1938) from Korea has similar male pore structure to A. bimontis . However, A. koreanus is larger (length 93–103 mm and greatest diameter 4.5 mm), has variable numbers of spermathecae from zero to one in VI or VII, no setae on clitellum for fully matured individuals, and has higher setal number than A. bimontis with 43–46 in VI, 43–52 in XX and 18–24 setae between male pores ( Kobayashi 1938a). Furthermore, one or two small papillae arranged in a transverse row medial to the male pore are present in A koreanus . Spermathecae of A. koreanus are absent or rudimentary and its prostate glands are absent or small in XVIII or XVII–XIX ( Kobayashi 1938a). The original description of A. koreanus was based on 11 clitellates ( Kobayashi 1938a). Among them, seven individuals were athecate, three had a single spermatheca in segment VII, and the remaining individual had two spermathecae with one in right VII and the other in left VI. It seems that A. koreanus might be parthenogenetic.

The arrangement of genital papillae in the male pore area of A. bimontis is also similar to that of Amynthas shinkeiensis (Kobayashi, 1938) from Korea. Amynthas shinkeiensis is a quadrithecate earthworm with two pairs of spermathecal pores in intersegmental furrows of 6/7/8 ( Kobayashi 1938a). It has higher setal number than A. bimontis with 46 in VII, 53 in XX and 16 between male pores, but has no setae on the clitellum. In addition, prostate glands and prostatic ducts are entirely absent in A. shinkeiensis and its spermathecae are vestigial without diverticulum ( Kobayashi 1938a). Therefore, the two species can be easily distinguished.

Figures

Figure 3. Amynthas bimontis sp. nov. Holotype (TESRI-O-H-38) (voucher number: MTS 105). (A) Ventral view of spermathecal pore region (sp, spermathecal pore); (B) ventral view of male pore region (gp, genital papilla; mp, male porophore); (C) dorsal view of left spermathecae (amp, ampulla; dv, diverticulum); (D) dorsal view of left prostate gland (ag, accessory gland; pd, prostatic duct); (E) dorsal view of right prostate gland. Scale bar 1 mm.