Amynthas minhdam Nguyen & Tran, 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 : 286-288

Amynthas minhdam Nguyen & Tran , sp. nov.

( Figure 5 )

Examined material. Holotype: 1 mature (complete body), ( CTU-EW.168.h01), natural forest (10°24’21”N, 107°16’18”E), 33 m, the foothill of Minh Dam Mts , Long Hai town , Long Dien District, Ba Ria – Vung Tau Province, 25 October 2016, coll. Nguyen Phuc Hau. Paratypes: 1 mature ( CTU-EW.168.p02), same data as for holotype; 3 matures (complete body) ( CTU-EW.168.p03) and 2 matures ( IEBR-EW.168.p03) same data as for holotype, but 17 October 2019, coll. Lam Hai Dang.

Etymology. minhdam , a noun in apposition, to emphasize the Minh Dam Mountain where the type specimens were collected.

Diagnosis. Small-medium size, length 59–65 mm, diameter 3.0–5.0 mm, segments 75–87. Prostomium 1/3 epilobous. First dorsal pore in 12/13. Setal numbers: 48–53 in viii, 63–67 in xxx, 7–9 between two male porophores in xviii. Two pairs of spermathecal pores located lateroventrally in intersegments 5/6/7. One medioventral pre-setal genital marking, often accompanied by one pair of markings on setal ring in vii. Ventral distance between two male pores about 0.3x circumference. A pair of genital markings located medially in xviii. Holandric. Testis sac connected. Intestinal caeca simple. Septa 8/9/10 absent.

Description. Body cylindrical, small size, length 59–65 mm, diameter 3.0–5.0 mm, weight 0.2–0.25 gr, segments 75–87. Body transparent, uniformly pale, clitellum light brown. Prostomium 1/3 epilobous. First dorsal pore in 12/13. Setae perichaetine, pre-clitellar setae stouter and sparser than post-clitellar ones; setal numbers: 48–53 in viii, 63–67in xxx, 7–9 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.

Two pairs of spermathecal pores located lateroventrally in intersegments 5/6/7. One genital marking in vii, presetal and medioventral, an additional pair of genital markings on the setal ring vii, behind spermathecal pores. Male porophores located on the setal ring xviii; ventral distance between two male pores about 0.3X body circumference. A pair of genital markings (same size as male porophores) located medially in the setal ring xviii.

Septa 5/6/7/8 thick, 8/9/10 absent, 10/11/12/13 thick. 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. Typhlosole simple, lamelliform. Lymph glands absent.

Spermathecae paired in vi and vii. Ampulla oval-shaped; ducts about 1/3 ampulla. Diverticula thin, shorter than ampulla, directly attached to the base of ampullar duct; seminal chamber small, sub-divided by constrictions into 4–5 parts (chain-formed). Spermathecal ducts without nephridia. Accessory glands mushroom-shaped in vii, 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 xvii–xx; ducts long, waved and directly attached to body wall. A pair of large, mushroom-shaped accessory glands in association with genital markings in xviii.

Habitat. The species was found under the litter layers, but on the soil surface.

Remarks. The species can be assigned to the A. morrisi group due to having two pairs of spermathecal pores in 5/6/7 and holandry ( Sims & Easton 1972). To date, this group comprises 47 species, of which 13 have been recorded in northern and central Vietnam ( Thai 1982, 1984a,b; Le 1995; Pham 1995; Do et al. 1994, 1995; Nguyen et al. 2016a).

Within the A. morrisi group, the new species is fairly similar to A. sapinianus ( Chen, 1946) and A. morrisi ( Beddard, 1892) in having round genital markings paired in xviii, medially of the male pores, spermathecal pores located lateroventrally and caeca simple. A. minhdam sp. nov. differs from A. sapinianus in the presence of genital markings in the spermathecal region and the chain-shaped seminal chamber of the spermathecal diverticulum (vs. absence of genital markings, clavate-shaped seminal chamber) ( Chen 1946).

A. minhdam sp. nov. is also differentiated from A. morrisi in having one pair of genital markings located ventrally next to the male pores, on the setal ring of xviii, first dorsal pore in 12/13, and a chain-shaped seminal chamber. Instead, A. morrisi has the first dorsal pore in 10/11 or 11/12 and a clavate-shaped seminal chamber ( Blakemore 2002, Chang et al. 2016). The genital markings are very variable in Amynthas morrisi ( Chang et al. 2016) , but these variations do not appear to include the pattern characteristic of the new species. A. morrisi has pre-clitellar genital markings paired and/or unpaired small discs varying in numbers and positions; paired on some of vi–ix, median to spermathecal pore; unpaired on some of v–ix, midventral, pre-setal; and post-clitellar markings of two immediately median to each male porophore, one pre-setal and one post-setal, one of the two sometimes absent, slightly larger than the porophore, surrounded by several concentric furrows.Additional presetal markings on xviii and xix in some specimens, mid-ventral or median to male pores, numbers variable ( Chang et al. 2016).

The new species, A. minhdam sp. nov., is also similar to A. brevicapitatus (Thai, 1984) , A. deonganganus (Thai, 1984) and A. duplicoecus ( Thai, 1982) in having one pair of genital markings in xviii, median to the male pore. However, the new species differs from these three new species in having two pairs of spermathecal pores in 5/6/7 (vs. two pairs in 7/8/ 9 in A. brevicapitatus , three pairs in 5/6/7/ 8 in A. deonganganus , four pairs in 5/6/7/8/ 9 in A. duplicoecus ). A. minhdam sp. nov. also differs from A. deonganganus and A. duplicoecus in having first dorsal pore in 12/13 (vs. 11/12 and 5/ 6 in A. deonganganus and A. duplicoecus , respectively) and simple intestinal caeca (vs. manicate caeca). Two species, A. minhdam sp. nov. and A. brevicapitatus also share the character state of simple intestinal caeca, but they are clearly distinguished by the following: A. minhdam sp. nov. has spermathecal pores in lateroventrally 5/6/7, first dorsal pore in 12/13, a pair of genital markings in the male region, chain-shaped seminal chamber; while A. brevicapitatus has spermathecal pores in laterally 7/8/9, first dorsal pore in 11/12, more than one pair of genital markings in the male region and clavate-shaped seminal chamber.

Figures

FIGURE 5. Amynthas minhdam sp. nov. Holotype (CTU–EW.168.h01). A. Male region, ventral view. B. Spermathecal region, ventral view. C. Testis sacs and seminal vesicle. D. Left intestinal caecum. E. Left prostate gland. F. Left spermatheca. G. Prostate gland (comp. E). H. Male region (comp. A). I. Spermathecae (comp. F). J. Intestinal caecum (comp. D). Scale bar = 1 mm.