Amynthas yichunensis 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 : 286-289

Amynthas yichunensis Sun & Jiang , sp. nov.

( Figures 2–3 )

Type material. Holotype. One clitellate specimen (P1CJJXNN210604061Q01-01A), Yifeng County, Yichun City, Jiangxi Province, China ( 28°21′24″ N, 114°42′34″ E), at 112 m above sea level (asl). Habitat characterized as ferrosols in an orchard with kiwi, and surrounded by Metasequoia , hilly landform. The ground temperature was 18°C at the time of collection on June 4, 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 119 specimens are presented in Table 2.

Etymology. The specific epithet yichunensis is derived from “Yichun”, the city where the holotype and several selected paratypes of this new species were collected, thereby reflecting the geographical origin of the species. The Chinese name for this species is âǝḭŝē.

Diagnosis. length 66–105 mm, diameter 3.8–6.2 mm, segments 101–138, medium to large size. First dorsal pore at 9/10 or 10/11 or 11/12. Setal numbers: 32–38/III, 30–46/V, 40–50/VIII, 48–60/XX, 48–56/ XXV. Spermathecal pores 0, 1, or 2 pairs at 8/9 or 7/8–8/9. Genital markings, when present, single or paired on VIII and IX. Male pores spaced approximately 0.33 ventral circumference apart. Each male porophore with 1 or 2 genital papillae, sometimes none; and an additional pair in center of XVIII. Intestinal caeca simple. Spermathecae 0, 1 pair, or 2 pairs, with or without diverticula.

Description.

External morphology. Coloration of preserved specimens khaki on the dorsal surface and a pale khaki on the ventral surface. A reddish brown mid-dorsal line visible posterior to the clitellum. The specimens about 66–105 mm in length and 3.8–6.2 mm in diameter at the clitellum, and 101–138 segments. Secondary annulations present as two annular lines per segment in segments VII – X. The prostomium ½ epilobous. The first dorsal pore located at intersegmental furrows 9/10 or 10/11 or 11/12. The clitellum annular within XIV–XVI,, unpigmented, smooth, and swollen, and without setae on the ventral side. Setae uniformly distributed, with setal formula: AA = 1.2–1.3AB, ZZ = 1.6–1.9ZY; setal numbers: 32–38 on segment III, 30–46 on segment V, 40–50 on segment VIII, 48–60 on segment XX, and 48–56 on segment XXV. When present, 18–19 setae observed between spermathecal pores on segment VIII, and 12–19 setae between the male pores. Spermathecal pores not visible externally in the holotype. Two pairs of small genital papillae present anterior to the setal rings of segments VIII and IX ( Fig. 2A ). A single pair of male pores located on segment XVIII, separated by approximately one-third of the total body circumference on the ventral side, with each situated on a rounded, glandular, raised porophore. A small, oval genital papilla located anterior and slightly medial to the porophore, with another positioned posteriorly and slightly medially. Three concentric skin folds surrounding each male pore and the associated genital papillae ( Fig. 2B ). A single female pore, elliptical in shape and slightly depressed, located mid-ventrally on segment XIV .

Internal morphology. Septa 8/9–9/10 absent, septa 5/6–7/8 thickened and muscular, while septa 10/11–14/15 thicker than those posterior to them. A single dorsal blood vessel extending continuously into the pharynx. Four pairs of esophageal hearts present in segments X–XIII, with the first pair slender and the remaining three pairs well developed. A bucket-like gizzard present in segments VIII– X; intestinal swelling is observed in segment XVI. 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. 2C ). Testis-sacs present in segments X and XI; the first pair oval, with two lobes separated ventro-medially; the second pair of testis-sacs and first pair of seminal vesicles enclosed in a membranous sac. Well-developed seminal vesicles present in segments XI and XII, and separated ventro-medially. The prostate gland well-developed, with large lobules extending from the posterior half of segment XVI to segment XX; the prostatic duct U-shaped and located in segment XVIII, with the dorsal side thinner than the ventral side ( Fig. 2D ). Accessory glands not visible on segment XVIII. Spermathecae and diverticula absent in both the holotype and paratype P1CJJXNN210525940 R02-01 . Paratype P1CJJXNN210609889 R03-02 having one pair of spermathecae in segment IX, measuring 1.4 mm in length. The ampulla oval-shaped and clearly separated from its duct, about one-third the length of the ampulla and without a diverticulum. Paratypes P1CJJXNN210604061 R05- 01 , P1CJJXNN210520933 R02-01 , P1CJJXNN210518936 R05-01 , and P1CJJXNN210609889Q01-02 having two pairs of spermathecae in segments VIII and IX, each measuring 1.9 mm in length. The ampullae irregularly spherical and clearly separated from the ducts, about from one-sixth to one-half the length of the ampullae and without diverticula. Paratype P1CJJXNN210607920 R03-02 having two pairs of spermathecae located in segments VIII and IX, and measure 1.8 mm in length. The heart-shaped ampullae clearly separated from the ducts, equal in length to the ampullae. The diverticula three-fifths the length of the main spermathecal axis, lacking distal expansion, and degenerated into buds except for the seminal chamber on the right side of segment IX.

Morphological variations. The variations in the number and position of spermathecal pores, as well as in the characteristics of the spermathecal and male pore regions across different specimens, are detailed in Table 3 and Fig. 3 . This comprehensive account aims to elucidate the range of morphological variations observed within the population studied herein, thereby advancing the understanding of species taxonomy and evolutionary biology.

Figures

FIGURE 2. Amynthas yichunensis Sun & Jiang, sp. nov. Holotype (P1CJJXNN210604061Q01-01A). A. Ventral view of spermathecal pore region. B. Ventral view of male pore region. C. Intestinal cecum. D. Prostate gland. Paratype (P1CJJXNN210525940R02-01, P1CJJXNN210609889R03-02, P1CJJXNN210604061R05-01, P1CJJXNN210520933R02- 01, P1CJJXNN210518936R05-01, and P1CJJXNN210609889Q01-02). E. The style of Spermathecae. Paratype (P1CJJXNN210607920R03-02). F. The style of Spermathecae. Scale bars = 1 mm. Abbreviations: mp (male pore), gp (genital papilla).

FIGURE 3. Amynthas yichunensis Sun & Jiang, sp. nov. Ventral views of paratypes: A–D, spermathecal pore regions; E–K, male pore region. Specimen codes: A and F, P1CJJXNN210607920R03-02; B and I, P1CJJXNN210518936R05-01; C and J, P1CJJXNN210609889R03-02; D and K, P1CJJXNN210609889Q01-02; E. P1CJJXNN210604061R01-02; G. P1CJJXNN210520933R02-01; H. P1CJJXNN210525940R02-01. Scale bars = 1 mm. Abbreviations: sp (spermathecal pore), mp (male pore), gp (genital papilla).