Amynthas shangraoensis Sun & Jiang, 2025

Sun, Jing, Wang, Ding-Yi, Qiu, Jiang-Ping, Jiang, Ji-Bao & Liu, Man-Qiang, 2025, Three newly discovered species of Amynthas earthworms (Oligochaeta: Megascolecidae) from Jiangxi Province and adjacent regions of China, Zootaxa 5729 (2), pp. 283-314 : 306-313

Amynthas shangraoensis Sun & Jiang , sp. nov.

( Figures 6–7 )

Type material. Holotype. One clitellate specimen (P1CJJXNN210527067N01-02) was collected from Poyang County, Shangrao City, Jiangxi Province, China ( 29°12′45″ N, 116°53′27″ E), at 42 m asl, in ferralsols with a farmland planted with oilseed rape, adjacent to a vegetable field, in a hilly landform. The ground temperature was 23.7°C at the time of collection on May 27, 2021. Collectors: X. X. Qi, D. Wu, K. H. Jiao, C. Z. Zhang, X. Gong, M. G. Xu, and Y. Zhang.

Paratypes. A total of 3 specimens were collected, which are described hereafter. One clitellate specimen (P1CJJXNN210603065N03-01) was collected from Ganzhou Town , Fengxin County, Yichun City, Jiangxi Province, China ( 28°48′20″ N, 115°25′12″ E), at 57 m asl, in ferralsols within wet farmland planted with oilseed rape in a hilly landform. The ground temperature was 20.8°C at the time of collection on June 3, 2021. Collectors: X. X. Qi, D. Wu, K. H. Jiao, C. Z. Zhang, X. Gong, M. G. Xu, and Y. Zhang.

One clitellate specimen (P1CJJXNN210521062N01-02) was collected from Shangfang Township , Wannian County, Shangrao City, Jiangxi Province, China ( 28°40′33″ N, 117°3′39″ E), at 52 m asl, in fluvo-aquic soil within a farmland planted with maize and treated with organic fertilizer, in a hilly landform. The ground temperature was 25.2°C at the time of collection on May 21, 2021. Collectors: X. X. Qi, D. Wu, K. H. Jiao, C. Z. Zhang, X. Gong, M. G. Xu, and Y. Zhang.

One clitellate specimen (P1CJJXNN210521062Q02-01) was collected from Shangfang Township , Wannian County, Shangrao City, Jiangxi Province, China ( 28°40′59″ N, 117°1′21″ E), at 68 m asl in fluvo-aquic soil within an orchard with grapes, chickens, and geese, in a hilly landform. The ground temperature was 23.3°C at the time of collection on May 21, 2021. Collectors: X. X. Qi, D. Wu, K. H. Jiao, C. Z. Zhang, X. Gong, M. G. Xu, and Y. Zhang.

Etymology. The name shangraoensis is derived from the Latinized form of “Shangrao”, referring to the native region where this type specimen was collected. The Chinese name for this species is 上ẑḭŝē.

Diagnosis. New species, length 109–147 mm, diameter 4.5–5.1 mm, segments 128–145, medium to large size. Prostomium ½ epilobous. First dorsal pore at 12/13. Setal numbers: 20–28/III, 28–32/V, 34–50/VIII, 36–56/XX, 40–52/XXV. Four pairs of spermathecal pores in 5/6–8/9. Genital markings: one, one pair, or two pairs present on VIII and IX. Male pores spaced 0.4 total circumference ventrally apart. Each male porophore with one or two genital papillae; additional pair located centrally on XVIII. Intestinal caeca simple. Four pairs of spermathecae in VI–IX, increasing in length from the first to the fourth pair.

Description.

External morphology. Preserved specimens: a light brown coloration on the dorsal surface and lack pigmentation on the ventral surface. The mid-dorsal line distinctly pigmented. The specimens about 109–147 mm in length and 4.5–5.1 mm in width at the clitellum, and 128–145 segments. Segments 7–13 with two secondary annulations each. The prostomium ½ epilobous. The first dorsal pore located in intersegmental furrow 12/13. The clitellum annular and located in segments XIV–XVI, smooth, swollen, slightly whitish, without ventral setae and dorsal pores. Setae uniformly distributed, with 20–28 setae on segment III, 28–32 on segment V, 34–50 on segment VIII, 36–56 on segment XX, and 40–52 on segment XXV. Additionally, 9–10, 10–11, and 13–15 setae present between the spermathecal pores on segments VI, VII, and VIII, respectively, while 13–18 setae present between the male pores. The setal formula: AA = 1.1–1.2AB, ZZ = 1.8–2.0ZY. Four pairs of spermathecal pores present in intersegmental furrows 5/6–8/9, spaced approximately one-third of the total body circumference and located on the ventral side. The pores conspicuous, eye-like in appearance, with slightly raised bases. A small round genital papilla present anterior to the right seta d on segments VIII and IX ( Fig. 6A ). Male pores present on segment XVIII, spaced approximately 0.4 of the total body circumference and located on the ventral side, with each situated in the center of a slightly raised elliptical porophore.A flat-topped genital papilla closely positioned posterior to and slightly medial to the male pore porophore ( Fig. 6B ). A single female pore located mid-ventrally in segment XIV, milky-white, elliptical, and slightly umbilicated.

Internal morphology. Septa 8/9–9/10 absent; septa 5/6–7/8 and 10/11–11/12 thickened and muscular,;septa 12/13–13/14 thicker than the more posterior septa.A single dorsal blood vessel extends continuously to the pharynx. Four pairs of esophageal hearts present in segments X–XIII, with the anterior-most pair more slender than the others. A bucket-shaped gizzard present in segments VIII–X. Intestinal enlargement observed in segment XV. The intestinal caeca simple, originating in segment XXVII and extending anteriorly to segment XXIII, forming finger-shaped sacs with smooth dorsal and ventral margins ( Fig. 6C ). Oval, undeveloped testis-sacs present in segments X and XI, and the two lobes separated ventro-medially. Moderately developed seminal vesicles present in segments XI and XII, and the two lobes separated ventro-medially. A well-developed, hypertrophic, and lobulated prostate gland extends from segment XVI to the anterior half of segment XXI, and a U-shaped prostatic duct in present in segment XVIII, with the ventral side of the tube being thicker than the dorsal side ( Fig. 6D ). An irregular accessory gland attached to the body wall at the base of each prostatic tube in segment XVIII. Paired spermathecae present in segments VI–IX, with their lengths progressively increasing from the first to fourth pair in both the holotype and paratypes. The first, second, third, and fourth pairs measure 2 mm, 2.3 mm, 2.3 mm, and 2.6 mm, respectively, in the holotype. The ampullae in segment VI rod-shaped, and attached to ducts of medium thickness. The boundaries between the ampullae and ducts distinct, and the ducts approximately one-third the length of the ampullae. The ampullae in segment VII slim and heart-shaped, with well-developed ducts and clear boundaries between the ampullae and ducts. The ducts approximately one-third the length of the ampullae. The ampullae in segment VIII heart-shaped, with well-developed ducts approximately half the length of the ampullae. The ampullae in segment IX heart-shaped, with short, well-developed ducts approximately one-third the length of the ampullae. The first pair of diverticula approximately three-fifths the length of the main spermathecal axis, thin, straight, and without anterior enlargement. The second pair of diverticula approximately two-thirds the length of the main spermathecal axis, with the anterior one-fourth slightly enlarged into a seminal chamber. The third pair of diverticula approximately three-fourths the length of the main spermathecal axis, with the anterior one-fourth slightly enlarged into a seminal chamber. The fourth pair approximately two-thirds the length of the main spermathecal axis, with the anterior one-third expanded into a rod-shaped seminal chamber. An irregular accessory gland present near the ventral midline in segments VIII and IX; the spermathecal ducts without nephridia ( Fig. 6E ).

Morphological variations. Compared to those in the holotype, the number and position of the genital papillae within the spermathecal and male pore regions vary across all paratype specimens ( Table 7, Fig. 7 ).

DNA barcodes. GenBank accession numbers:

OR785030 (P1CJJXNN210527067N01-02, holotype);

OR785032 (P1CJJXNN210603065N03-01, paratype);

OR785033 (P1CJJXNN210521062N01-02, paratype);

OR785034 (P1CJJXNN210521062Q02-01, paratype).

Remarks. The new species, A. shangraoensis Sun & Jiang , sp. nov. is classified within the A. corticis group according to the classification scheme of Sims & Easton (1972). A comprehensive examination of all species within the A. corticis group reveals that four species, namely, A. corticis (Kinberg, 1867) , A. carnosus (Goto & Hatai, 1899) , A. heterochaetus (Michaelsen, 1869) , and A. nanshanensis Shen, Tsai & Tsai, 2003 , exhibit certain morphological similarities to A. shangraoensis Sun & Jiang , sp. nov. ( Table 8). Notably, the number and position of spermathecal pores in A. carnosus are variable, ranging from three pairs at intersegmental furrow 5/6–7/8 and 6/7–8/9, to four pairs on 5/6–8/9, and five pairs on 4/5–8/9 ( Han et al., 2024; Sims & Easton, 1972). For the purpose of comparison in this study, we focused on A. carnosus specimens with four pairs of spermathecal pores.

Comparison of A. shangraoensis sp. nov. with A. corticis reveals several distinctive morphological characteristics. A. corticis exhibits a broader range of body lengths ( 96–184 mm) and narrower widths (3.0–5.0 mm) relative to the more consistent dimensions of A. shangraoensis sp. nov., which measures 109–147 mm in length and 4.5–5.1 mm in width. Although both species possess four pairs of spermathecal pores in intersegmental furrows 5/6–8/9, A. shangraoensis sp. nov. is distinguished by a progressive increase in spermathecal length from the first to the fourth pair. The prostate gland varies from well-developed to rudimentary or absent in A. corticis , while maintaining consistent development and possessing large lobules in A. shangraoensis sp. nov. Additionally, A. corticis is distinguished by the absence of accessory glands in the spermathecal region, unlike A. shangraoensis sp. nov., which possesses irregular accessory glands in segments VIII and IX.

A. carnosus exhibits a larger body size, measuring 130–240 mm in length and 6.0– 8.3 mm in width, exceeding the dimensions of A. shangraoensis sp. nov., which measures 109–147 mm in length and 4.5–5.1 mm in width. The configuration of the spermathecal pore varies in A. carnosus , ranging from three pairs at intersegmental furrows 5/6–7/8 and 6/7–8/9, to four pairs at 5/6–8/9, and five pairs at 4/5–8/9. In contrast, four pairs of spermathecal pores are consistently observed at intersegmental furrows 5/6–8/9 of A. shangraoensis sp. nov. Furthermore, the arrangement of papillae within the spermathecal and male pore regions differs between the two species. Paired papillae are typically present in the spermathecal pore region of A. carnosus , whereas unpaired papillae are observed within the corresponding segments of A. shangraoensis sp. nov. The male pore region of A. carnosus typically bears two pairs of papillae between the male pores, whereas A. shangraoensis sp. nov. possesses a single pair of papillae posterior to the male pores.

There are distinct morphological characteristics between A. heterochaetus and the new species, A. shangraoensis sp. nov. The body size of A. heterochaetus (length 100–158 mm and width 3.0–5.0 mm) is approximately similar to that of A. shangraoensis sp. nov. (length 109–147 mm, width 4.5–5.1 mm). In A. heterochaetus , the first dorsal pore is located at intersegmental furrow 11/12, whereas in A. shangraoensis sp. nov., it is positioned at intersegmental furrow 12/13. Additionally, the four pairs of spermathecae in A. heterochaetus are of uniform length, whereas the length of spermathecae increases progressively from the first to the fourth pair in A. shangraoensis sp. nov. One of the key distinguishing characteristics is the presence of a well-developed prostate gland with large lobules in A. shangraoensis sp. nov., which is absent in A. heterochaetus . Additionally, A. shangraoensis sp. nov. possesses irregular accessory glands in segments VIII and IX, which are absent in A. heterochaetus .

Finally, a comparative analysis of the morphological characteristics of A. shangraoensis sp. nov. and A. nanshanensis reveals marked differences. A. nanshanensis has a significantly smaller body size, measuring 41–89 mm in length and 2.2–3.0 mm in width, compared to the larger A. shangraoensis sp. nov., which measures 109–147 mm in length and 4.5–5.1 mm in width. Additionally, A. nanshanensis possesses fewer segments (55–104) than A. shangraoensis sp. nov. (128–145). The first dorsal pore in A. nanshanensis is located at intersegmental furrow 5/6, whereas in A. shangraoensis sp. nov., it is positioned at intersegmental furrow 12/13. Finally, the spermathecae in A. shangraoensis sp. nov. increase progressively in length from the first to the fourth pair, whereas those in A. nanshanensis exhibit a uniform length.

Discussion

The NJ tree, an essential tool for analyzing evolutionary relationships ( Mang et al., 2022; Chang et al., 2005), was constructed in this study using DNA barcoding data. The DNA barcodes of the species mentioned in the “Remarks” above—those that exhibit morphological similarity to the new species—were selected for constructing the NJ tree. Analysis of the NJ tree demonstrated the distinctiveness of the three newly described species ( A. yichunensis , A. huizhouensis , and A. shangraoensis ), as evidenced by their significant genetic divergence from other known species within the Amynthas genus ( Fig. 8 ). This finding supports the taxonomic distinctiveness of the three Amynthas species described herein. The NJ tree indicated a closer genetic relationship between A. yichunensis and A. huizhouensis than with A. shangraoensis . Furthermore, the intraspecific genetic distance of A. shangraoensis was found to exceed that of the other two species, suggesting a higher degree of intraspecific differentiation within this species.

Sims & Easton (1972) established the species-group classification of the genus Amynthas based on variations in the position and number of spermathecal pores among specimens. The characteristics of spermathecae continue to serve as key morphological criteria for species identification. However, recent studies indicate an increasing number of species within the genus Amynthas exhibit intraspecific variations in the number and position of spermathecae ( Li et al., 2024).Additional research on intraspecific genetic diversity may elucidate the relationships among the number of spermathecal pores, species identification, and morphological variations in papillae. Therefore, investigation of the genetic basis underlying these variations and examination of the ecological adaptability of the new species will provide critical insights into their evolutionary significance within the Amynthas genus.

Figures

FIGURE 6. Amynthas shangraoensis Sun & Jiang, sp. nov. Holotype (P1CJJXNN210527067N01-02). A. Ventral view of spermathecal pore region, scale bar = 1 mm. B. Ventral view of male pore region, scale bar = 1 mm. C. Intestinal cecum. D. Prostate gland. E. Spermathecae, scale bar = 2 mm. Abbreviations: sp (spermathecal pore), mp (male pore), gp (genital papilla).

FIGURE 7. Amynthas shangraoensis Sun & Jiang, sp. nov. Ventral views of paratypes: A–C. Spermathecal pore regions; D–F. Male pore regions. Specimen codes: A and D, P1CJJXNN210603065N03-01; B and E, P1CJJXNN210521062N01-02; C and F, P1CJJXNN210521062Q02-01. Scale bars = 1 mm. Abbreviations: sp (spermathecal pore), mp (male pore), gp (genital papilla).

FIGURE 8. The phylogenetic tree constructed using the neighbor-joining method based on COI gene for the three new species and related species