Amynthas popi Shen & Chang, 2025

Shen, Huei-Ping & Chang, Chih-Han, 2025, A new earthworm species of the genus Amynthas (Clitellata: Megascolecidae) from northern Taiwan, false synonymy between Amynthas corticis (Kinberg, 1867) and Amynthas sheni (Chen, 1935) and other taxonomic issues relating to A. corticis, Zootaxa 5589 (1), pp. 112-126 : 114-119

Amynthas popi Shen & Chang , sp. nov.

( Figure 1 )

Holotype: Clitellate (mature) specimen (312 mm in total length, dissected), along Rural Highway Tao119, Fuhsing , Taoyuan City, 24°49'40.85''N, 121°22'50.25''E, 7 April 2022, Chieh Kao ( NTUM-EW-09352 ).

Paratypes: 1 clitellate (dissected), along a hiking trail to Juansi Waterfall , Shihlin, Taipei City, 25°09'19.38''N, 121°33'56.29''E, 23 September 2010, Wen-Jay Chih & Chi-Lun Li ( NTUM-EW-07908 ); 1 clitellate, along Rural Highway Tao119, Fuhsing, Taoyuan City, 24°50'08.02''N, 121°23'32.55''E, 4 March 2022, Chieh Kao ( NTUM-EW-09336 ) .

Other material. 1 aclitellate along a hiking trail to Juansi Waterfall , Shihlin, Taipei City, 25°09'19.38''N, 121°33'56.29''E, 23 September 2010, Wen-Jay Chih & Chi-Lun Li ( NTUM-EW-08072 ); 1 clitellate along a rural highway to Mt. Zhuzi , Beitou, Taipei City, 25°11'32.73''N, 121°32'46.76''E, 29 October 2011, Wen-Jay Chih ( NTUM-EW-08360 ); 1 clitellate along a hiking trail to Miantian Pond , Tamsui, New Taipei City, 25°10'18.76''N, 121°30'30.18''E, 20 April 2012, Wen-Jay Chih ( NTUM-EW-08700 ) .

Diagnosis. Large earthworm. Length (clitellates) 210–316 mm. Segments numbering 138–150. Setae 54–60 in VII, 63–92 in XX, 12–15 between male pores. First dorsal pore in 12/13. Clitellum XIV–XVI. Spermathecal pores four pairs in 5/6–8/9, 0.19–0.24 body circumference ventrally apart. Preclitellar papillae closely or widely paired in presetal VIII. Male pores 0.25–0.31 body circumference ventrally apart in XVIII, with a postsetal papilla medial to each pore. Postclitellar papillae often widely paired in postsetal XIX, and occasionally with additional, more closely paired papillae in presetal XIX. Spermathecae four pairs in VI–IX. Seminal vesicles small, two pairs in XI and XII. Prostate glands compact, confined to XVIII, divided into upper and lower two main lobes. Prostatic ducts short, stout, horizontal, confined to XVIII, extending slightly downward at distal end. Accessory glands absent.

Description. External: Length (clitellates) 210–316 mm. Segments numbering 138–150. Clitellum XIV–XVI, setae and dorsal pores absent, 5.23–7.51 mm in length and 7.25–8.6 mm in width. Prostomium epilobous. Three annuli (secondary segments) per segment in VI–XIII. Setal number 54–60 in VII, 63–92 in XX, and 12–15 between male pores in XVIII. First dorsal pore in 12/13. Spermathecal pores four pairs in intersegmental furrows of 5/6–8/9 ( Fig. 1A ), distance between paired pores 0.19–0.24 body circumference ventrally apart. Genital papillae closely paired in presetal VIII for two specimens ( Fig. 1B ), widely paired in presetal VIII for one specimen ( Fig. 1C ), one in the middle of presetal VII and one on right side of presetal VIII for one specimen ( Fig. 1A ), preclitellar region damaged for one specimen, and papillae not visible in the aclitellate specimen. Each papilla round, 1.0– 2.15 mm in diameter. Female pore single, mid-ventral in XIV. Male pores paired in XVIII, 0.25–0.31 body circumference ventrally apart, each situated on a round porophore about 1.0 mm in diameter, with a postsetal papilla medial to it, each papilla 0.75–1.0 mm in diameter. Genital papillae often widely paired in postsetal XIX ( Fig. 1D ), and occasionally with additional, more closely paired papillae in presetal XIX ( Fig. 1E ). For all six specimens examined, papillae widely paired in postsetal XIX for four specimens and two of them with an additional pair in presetal XIX, only one papilla on right side of postsetal XIX for one specimen, and papillae not visible in the aclitellate specimen. Each papilla round, with a slightly concave center, 1.0– 1.25 mm in diameter. Live worms pinkish or grayish with white or dark brown clitellum. Preserved specimens white and slightly darker on clitellum.

Internal: Septa 5/6–7/8 thick, 8/9 membranous, 9/10 absent, 10/11–12/13 muscular, thickened, 13/14 thick. Nephridial tufts on anterior faces of 5/6/7. Gizzard large, round in VIII–X. Intestine enlarged from XV. Intestinal caeca paired in XXVII, simple, extending anteriorly to XXIV. Esophageal hearts paired in XI–XIII. Spermathecae four pairs in VI–IX ( Fig. 1F ), ampulla elongated oval-shaped, surface wrinkled, 2.28–2.69 mm long and 1.35–2.13 mm wide, spermathecal duct stout, 0.56–1.63 mm in length. Diverticulum stalk straight or bent, 1.7–2.09 mm in length, seminal chamber oval, iridescent, 0.4–0.79 mm long. Accessory glands absent. Holandric. Testes round, two pairs in ventrally joined sacs in X and XI. Seminal vesicles small, two pairs in XI and XII, occupying 1/2–2/3 of the segmental compartment. Prostate glands compact, paired, confined to XVIII ( Fig. 1G ), divided into two main lobes: upper and lower. Prostatic ducts short, stout, horizontal, confined to XVIII, extending slightly downward at distal end. Accessory glands absent.

DNA barcodes. GenBank accession numbers PP960539 ( NTUM-EW-09352 , holotype), PP960536 ( NTUM-EW-07908 , paratype), PP960538 ( NTUM-EW-09336 , paratype), and PP960537 ( NTUM-EW-08072 ) ( Table 1 ).

Etymology. The name popi is in memory of Victor V. Pop, a warm and pleasant earthworm taxonomist.

Remarks. It is unusual for a large earthworm like Amynthas popi sp. nov. to have compact prostate glands together with short, stout and horizontal prostatic ducts confined to segment XVIII among the native Amynthas earthworms known from Taiwan. The morphological character with one postsetal papilla medial to each male porophore of A. popi is fairly similar to that of A. corticis , Amynthas carnosus ( Goto & Hatai, 1899) , Amynthas biorbis Tsai & Shen, 2010 , and Amynthas shengtangmontis Dong & Jiang, 2019 . Amynthas corticis has variable papilla arrangements with number of papilla ranging from zero to two, occasionally three, around each male porophore, and individuals with one postsetal papilla medial to each male porophore are common ( Fig. 2A ). Amynthas carnosus has a large postsetal papilla medial to each male and closely or widely paired papillae in presetal VIII–IX and XVIII–XIX ( Chang et al. 2016). Amynthas biorbis has a large postsetal papilla medial to each male porophore ( Tsai et al. 2010), but individuals without such a papilla were found in subsequent collections. As for A. shengtangmontis , there is discrepancy between its description and figure ( Figure 4 in Dong et al. 2019). Dong et al. (2019, p. 34) state in the diagnosis section of A. shengtangmontis that “Four pairs of postsetal genital papillae arranged in VI–IX…One pair of male pores in XVIII, each on the top of a large raised, round porophore…with one presetal indented-topped genital papilla medial of each porophore”. Similar descriptions also appear in the remarks section and Table 4 of Dong et al. (2019). However, Figure 4 in Dong et al. (2019) shows four pairs of presetal genital papillae in VI–IX and one postsetal papilla medial to each male porophore. We think that what illustrated in the figure takes precedence over text. All the aforementioned species are octothecal with four pairs of spermathecae in VI–IX. Their characters are compared in Table 3 . All four species are morphologically distinguishable from A. popi : A. corticis is smaller, and has fewer segments, lower setal number, papillae in presetal VI–IX, prostate glands absent or rudimentary, C- or U-shaped prostatic ducts, and stalked accessory glands; A. carnosus has closely or widely paired papillae in presetal VIII–IX and XVIII–XIX, large prostate glands in 1/2XVI–XIX, U-shaped prostatic ducts, and round accessory glands; A. biorbis is much smaller, and has fewer segments, lower setal number, no papilla except the one medial to each male pore, large prostate glands in XVI–XX, U-shaped prostatic ducts, and large, sessile accessory glands; A. shengtangmontis is smaller, and has fewer segments, lower setal number, papillae in presetal VI–IX, four pairs of esophageal hearts in X–XIII, well-developed seminal vesicles, large prostate glands in XV–XXII, U-shaped prostatic ducts, and stalked accessory glands ( Table 3 ). The postclitellar genital papilla arrangement of A. popi also looks somewhat similar to that of Amynthas gageodo Blakemore, 2012 from South Korea. Amynthas gageodo is also octothecal, but it is smaller and has fewer segments, four pairs of esophageal hearts in X–XIII, moderately large seminal vesicles, and sessile accessory glands ( Table 3 ). There is no mention of prostate gland together with prostatic duct of A. gageodo in the original description, yet the morphology of this organ is shown in Figure 1 in Blakemore et al. (2012, p. 257). All the species mentioned above are genetically distinct ( Fig. 3 ; Table 4 ).

Amynthas rodericensis (Grube, 1879) , Amynthas sheni ( Chen, 1935) , Amynthas siam Blakemore, 2011 , Amynthas punicans Blakemore, 2015 , and Amynthas panhai Bantaowong et al., 2023 also have a postsetal papilla medial to each male porophore. These species are easily differentiated from A. popi morphologically. Amynthas rodericensis has large postsetal papillae reaching intersegmental furrow of 18/19 and four pairs of dorsally positioned spermathecal pores in 5/6–8/9 ( Chang et al. 2016). Amynthas sheni has postsetal papillae on VIII and occasionally also on IX, and has no spermatheca ( Chen 1935). Amynthas siam is much smaller with body length of 70–90 mm and has three pairs of spermathecae in segments VII–IX with diverticulum composed of narrow convoluted stalk and iridescent bulb ( Blakemore 2011). Amynthas punicans is much smaller with body length of 69 mm and has two pairs of spermathecae in segments VI–VII with long, zig-zagging spermathecal diverticula ( Blakemore et al. 2015). Amynthas panhai has widely paired postsetal papillae on VII and three pairs of spermathecae in segments VI–VIII with loosely coiled diverticula ( Bantaowong et al. 2023).

Figures

FIGURE 1. Amynthas popi sp. nov. A. Ventral view of spermathecal pore region of holotype (NTUM-EW-09352) (sp, spermathecal pore; gp, genital papilla). B. Ventral view of segment VIII of a paratype (NTUM-EW-09336). C. Ventral view of segment VIII of a 227-mm clitellate (NTUM-EW-08700). D. Ventral view of male pore region of a 227-mm clitellate (NTUM- EW-08700) (mp, male porophore). E. Ventral view of male pore region of holotype. F. Dorsal view of right spermathecae of holotype (amp, ampulla; dv, diverticulum). G. Dorsal view of right prostate gland of holotype (pd, prostatic duct). Scale bars = 1 mm.

FIGURE 2. Amynthas corticis (Kinberg, 1867). A. Ventral view of male pore region of a 123-mm clitellate (voucher number: cort5, GenBank accession number: JX290438) (mp, male porophore; gp, genital papilla). B. Ventral view of male pore region of a 124-mm clitellate (voucher number: cort6, GenBank accession number: JX290439). C. Ventral view of spermathecal pore region of a 124-mm clitellate (voucher number: cort6, GenBank accession number: JX290439) (sp, spermathecal pore). Scale bars = 1 mm.

FIGURE 3. DNA barcode tree inferred from the maximum likelihood analysis of the DNA sequences of the cytochrome c oxidase subunit I (COI) gene. Sequences acquired in this study and those available from Blakemore et al. (2012; 2015), Blakemore (2013a, b) and Blakemore & Lee (2013) were labeled with their voucher numbers. Sequences retrieved from GenBank were labeled with their GenBank accession numbers. The tree is rooted using Perionyx excavatus. Type materials are indicated in parentheses. Numbers around nodes are ultrafast bootstrap values above 50.

FIGURE 4. Photos of Amynthas sheni (Chen, 1935), type (USNM no. 20181). A. Ventral view of preclitellar papillae in segments VIII and IX. B. Ventral view of male pore region.