Amynthas longiprostaticus Nguyen & Lam, 2020

Nguyen, Tung T., Tran, Binh T. T., Lam, Dang H. & Nguyen, Anh D., 2020, Four new species of Amynthas earthworms in southeastern Vietnam (Annelida, Oligochaeta, Megascolecidae), Zootaxa 4790 (2), pp. 277-290 : 279-281

Amynthas longiprostaticus Nguyen & Lam , sp. nov.

( Figure 2 )

Material examined. Holotype: 1 mature (complete body), ( CTU-EW.088.h01), natural forests (11°25’31”N; 107°25’42”E), Cat Tien National Park, Tan Phu District , Dong Nai Province, 13 October 2013, coll. Le Van Nhan. Paratypes: 5 matures (complete body) ( CTU-EW.088.p02), 4 matures ( IEBR-EW.088.p02), same data as for holotype . Non-types: 30 matures (complete body), 1 mature (two fragments and two section slides), 4 immatures ( CTU-EW.088.03) same data as for holotype ; 17 matures (complete body) ( IEBR-EW.088.03), same data as for holotype .

Etymology. “ longiprostaticus ”, an adjective, to emphasize the long prostate gland.

Diagnosis. Small size, length 51–71 mm, diameter 2.4–2.7 mm, segments 81–112. Prostomium epilobous. First dorsal pore in 11/12. Setal numbers: 42–57 in viii, 49–66 in xxx, 9–12 between male porophores in xviii. A single pair of spermathecal pores, lateroventral, in intersegment 5/6. One pair of genital markings present ventrally in xviii. Septa 8/9/10 absent. Intestinal caeca simple. Holandric. Testis sacs separated. Prostate glands well developed, moderately lobuled, paired in xviii–xxviii; ducts long, waved and directly attached to body wall.

Description. Body cylindrical, small size; length 51–71 mm, diameter 2.4–2.7 mm, weight 0.2–0.3 gr, segments 81–112. Body light grey, ventrum paler than dorsum, clitellum darkish brown. Prostomium 1/3 epilobous. First dorsal pore in 11/12. Setae perichaetine, pre-clitellar setae stouter and sparser than post-clitellar ones; setal numbers: 42–57 in viii, 49–66 in xxx, 6–8 between male porophores in xviii; setal distance: aa>ab, zz>zy. Clitellum within xiv–xvi, without dorsal pores and setae. Female pore single, in midventral xiv.

A single pair of spermathecal pores located lateroventrally in intersegments 5/6. Genital markings single, located ventrally in front of setal rings of x or xi. Male porophores located on setal ring of xviii; ventral distance between two male pores about 0.35X body circumference. A single conial genital marking located ventrally, next to male pore.

Septa 5/6/7/8 thick, 8/9/10 absent, 10/11/12/13 thin. Oesophageal gizzard within viii–x. Intestinal origin at xv; caeca simple, originating at xxvii and extending anteriorly to xxii. Last hearts in xiii. Pharyngeal micronephridia developed 5/6/7. Typhlosole simple, lamelliform. Lymph glands absent.

A pair of spermathecae in vi. Ampulla oval-shaped; ducts about 1/2 ampulla, robust, but getting thinner basally. Diverticula thin, shorter than ampulla, strongly twisted, directly attached to the middle of ampullar duct; seminal chamber small, oval or bean-shaped. Spermathecal ducts without nephridia. A large accessory gland located next to each ampullar duct, sometimes covering the duct. Additional accessory gland with duct in x or xi, in association with external genital marking.

Holandric. Testis sacs developed, separated in x–xi. Seminal vesicles well developed in xi–xii. Ovaries well developed in 12/13. Ovisacs invisible. Prostate glands deeply lobuled, paired in xviii–xxviii; ducts long, waved and directly attached to body wall. A pair of large accessory glands in association with genital markings in xviii.

Habitat. The species was found in natural forests of Cat Tien National Park, where the forests are among the best-conserved in Vietnam. It was collected in the 0–10 cm mineral soil below a thick litter layer.

Remarks. The new species can be classified into the Amynthas minimus group characterized by one pair of spermathecal pores in 5/6 ( Sims & Easton 1972). This group is known to comprise 25 species ( Sims & Easton 1972; Thai 1982; Thai 1984a; Do et al. 1995; Pham 1995; Bantaowong et al. 2015), ten of which are known in northern and central Vietnam ( Nguyen et al. 2016a).

Within the A. minimus group, it is the only species with prostate glands that extend over up to 11 segments; in all other species the glands are shorter. Apart from that character, the new species is somewhat similar to A. papilio ( Gates, 1930) and A. khaohayod Bantaowong & Panha, 2015 (in Bantaowong et al. 2015), both also in the A. minimus group, by presence of a pair of genital markings in xviii and simple intestinal caeca. A. longiprostaticus sp. nov. differs from A. khaohayod in ventral distance between the two male porophores (0.35X vs. 0.18X), presence of genital markings in the spermathecal and male regions (vs. absence of genital markings), first dorsal pore in 11/12 (vs. in 12/13), and body size (length 51–71mm, diameter 2.4–2.7mm, vs. length 230mm, diameter 6.8–7.5mm), the shape of the male genital markings (conical-shaped vs. glandular-shaped) and the shape of spermathecae (ovalshaped ampulla small, oval or bean-shaped seminal chamber vs. spatulate-shaped ampulla, roughly elliptic seminal chamber). Similarly, the new species is also differentiated from A. papilio in the presence of genital markings in the spermathecal region (vs. absence of genital markings), first dorsal pore in 11/12 (vs. in 5/6), and size of genital markings in the male region (same size as male porophore vs. larger than male porophore, extending beyond xviii). In both species compared, the male genital markings are much larger than the ones in the new species, and the prostates are shorter.

The character state of exceptionally long prostate glands is, within Amynthas , shared by A. osmastoni ( Michaelsen, 1907) (xv–xxiv) and A. taiwumontis Shen, Chang, Li, Chih & Chen, 2013 (xvi–xxiv). However, A. osmastoni is longer than 250 mm and has three pairs of spermathecal pores in 6/7/8/9, first dorsal pore in 12/13, no genital markings in the male region. A. taiwumontis is about 130–150 mm long, has four pairs of spermathecal pores in 5/6/7/8/9, first dorsal pore in 11/12, and no markings in the male region. The new species differs from these two species in one pair of spermathecal pores in 5/6 and presence of genital markings in the male region, and has smaller size (55–71 mm long).

Regarding the morphology of the male region, the new species is fairly similar to A. brevicapitatus (Thai, 1984) , A. deonganganus (Thai, 1984) , A. corticis ( Kinberg, 1867) and to A. carnosus ( Goto & Hatai, 1899) , species with one pair of genital markings in immediate vicinity to the male pores. These three species differ from the new one in three or four pairs of spermathecae, connected testis sacs, and in a more anterior location of genital markings in the spermathecal region (when present), among other characters.

Figures

FIGURE 2. Amynthas longiprostaticus sp. nov. Holotype (CTU-EW.088.h01).A. Male region, ventral view. B. Left intestinal caecum. C. Left prostate gland. D. Spermathecal region, ventral view. E. Testis sacs and seminal vesicles. F. Right spermatheca. G. Male region (comp. A). H. Spermatheca (comp. F). I. Prostate gland (comp. C). J. Genital marking in x. K, L. Transverse section of male porophore, different section planes (Non-type: CTU-EW.088.03). Scale bars = 1 mm.