Amynthas ocularius 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 : 283-284

Amynthas ocularius Nguyen & Lam , sp. nov.

( Figure 4 )

Examined material. Holotype: 1 mature (complete body), ( CTU-EW.167.h01), natural forest (1032’51”N; 10730’47”E), 42m, Bung Rieng commune, Xuyen Moc District, Ba Ria – Vung Tau province, 25 October 2016, coll. Truong Thuy Ai. Paratypes: 2 matures (complete body), ( CTU-EW.167.p02) same data as for holotype; 3 matures (complete body), 1 mature (two fragments and two section slides) ( CTU-EW.167.p03) and 2 matures (IEBR- EW.167.p03) same data as for holotype, but 17 October 2019, coll. Lam Hai Dang.

Etymology. “ ocularius ”, an adjective, to emphasize the glasses-shaped arrangement of genital markings in the male region.

Diagnosis. Small size, length 65–68 mm, diameter 2.3–2.9 mm, segments 112–132. Prostomium 1/3 epilobous. First dorsal pore in 13/14. Setal numbers: 72–80 in viii, 61–75 in xxv, 7–8 between two male porophores in xviii. Three pairs of spermathecal pores in lateroventral intersegments 5/6/7/8. Four to eight pairs of pre- and post-setal genital markings arranged transversely in vii. Ventral distance between male pores about 0.3x body circumference. Genital markings numerous, organized to form a shape of glasses including two agglomerations of genital markings in 19/ 20 in line with male porophores and a transverse line of genital markings located behind the setal ring xix. Holandric. Testis sacs connected. Intestinal caeca simple. Septa 8/9/10 absent.

Description. Cylindrical body, small size, length 65–68 mm, diameter 2.3–2.9 mm, weight 0.1–0.2 gr, segments 112–132. Body transparent, uniformly pale; clitellum light brown. Prostomium 1/3 epilobous. First dorsal pore in 13/14. Setae perichaetine, pre-clitellar setae stouter and denser than post-clitellar ones; setal number: 72–80 in viii, 61–75 in xxv, 7–8 between two male porophores in xviii; setal distance: aa=ab, zz>zy. Clitellum within xiv–xvi, without dorsal pores, but with setae on ventrum xvi. Female pore single, in midventral xiv.

Three pairs of spermathecal pores located lateroventrally in intersegments 5/6/7/8. Four to eight pairs of genital markings arranged transversely in front of and behind the setal ring vii.

Male porophores located ventrally in the setal ring xviii; ventral distance between male pores about 0.3x body circumference. Genital markings numerous, organized to form a shape of glasses including two agglomerations of markings in 19/ 20 in line with male porophores, connected by a transverse line of markings located behind the setal ring xix.

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 xxv. Last hearts in xiii. Pharyngeal micronephridia developed in 5/6/7/8. Typhlosole simple, lamelliform. Lymph glands absent.

Spermathecae paired in vi, vii and viii. Ampulla oval-shaped; ducts about 1/2 ampulla, robust, but getting thinner basally. Diverticula thin, shorter than ampulla, strongly waved, directly attached to the base of ampullar duct; seminal chamber small, oval-shaped. Spermathecal ducts without nephridia. Four to five pairs of accessory glands in vii and viii, in association with genital markings.

Holandric. Testis sacs developed, connected in x–xi. Seminal vesicles well developed in xi–xii. Ovaries well developed in 12/13. Ovisacs invisible. Prostate glands deeply lobuled, paired in xvi–xxvi; ducts long, slightly waved and directly attached to body wall. Numerous accessory glands in association with genital markings.

Habitat. The species was found in the soil depth of 0–10cm.

Remarks. The arrangement of genital markings in the male region is unique among all species of Amynthas known so far. All markings are small, of same size, rounded: there is one unpaired midventral transverse line postsetal in xix, ending on both sides in an agglomeration covering xix/xx, i.e. in posterior of xix and anterior of xx, and in line with male porophores.

The species can be assigned to the A. gracilis species group because of the presence of three pairs of spermathecal pores in 5/6/7/8 and holandry ( Sims & Easton 1972, there as hawayanus -group). To date, the group comprises 63 species; of which 26 have been reported from Vietnam ( Thai 1982, 1984 b, 1984c; Thai & Samphon 1988; Do et al. 1994, 1995; Nguyen et al. 2016a).

Within the A. gracilis group, the new species is similar to A. compositus ( Gates, 1932) and A. papulosus ( Rosa, 1896) by having a large number of small, round, equal-sized genital markings in the spermathecal and male region, intestinal origin at xv, and simple intestinal caeca. However, A. ocularius sp. nov. differs from A. compositus in the first dorsal pore in 13/14, a line of pre-clitellar, pre-setal small, round genital markings in vii, and post-clitellar markings organized to form a shape of glasses including two agglomerations of markings in 19/ 20 in line with male porophores, connected by a transverse line of markings located behind the setal ring xix; whereas A. compositus has the first dorsal pore in 12/13, and the small, round genital markings are arranged in transverse rows in viii, xvii, xviii and xix, two rows of markings on viii, one presetal row of 10 markings, one postsetal row of 8 markings, the rows nearer to the setae than to the intersegmental furrows; four rows on xvii, two presetal and two postsetal; a single presetal row of 11 markings on xviii; two presetal markings near the midventral region on xix ( Gates 1932).

A. papulosus also differs from A. ocularius sp. nov. in having the first dorsal pore in 12/13, numerous markings in xviii–xx and agglomerated markings in vii–ix ( Rosa 1896; Thai & Samphon 1988).

A. ocularius sp. nov. is slightly similar to A. kinfumontis ( Chen, 1946) and to A. vuongmontis (Thai, 1984) by a transverse arrangement of genital markings in the male region. However, in A. kinfumontis , markings are present in xvii, xviii, 18/19 and xx, and spermathecal pores are at 7/8/9. In A. vuongmontis , markings are present in xvii, xix and xx, and they are absent in the spermathecal region; furthermore, spermathecal pores are located at 6/7/8/9.

Figures

FIGURE 4. Amynthas ocularius sp. nov. Holotype (CTU–EW.167.h01). A. Male region, ventral view. B. Left spermatheca. C. Spermathecal region, ventral view. D. Left intestinal caecum. E. Left prostate gland. F. Testis sacs and seminal vesicle. G. Spermathecae (comp. B). H. Male region (comp. A). I. Prostate gland (comp. E). J. Intestinal caecum (comp. D). K. Transverse section on genital markings (Paratype: CTU-EW.167.p03). Scale bar = 1 mm.