Amynthas dorsomorrioides Nguyen & Nguyen, 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 : 281-283

Amynthas dorsomorrioides Nguyen & Nguyen , sp. nov.

( Figure 3 )

Material examined. Holotype: 1 mature (complete body), ( CTU-EW.174.h01), shrubs and bushes (10°30’40”N, 107°07’37”E), 72 m, Kim Dinh commune, Ba Ria city, Ba Ria – Vung Tau province, 27 October 2016, coll. Nguyen Phuc Hau. Paratypes: 2 matures (complete body), ( CTU-EW.174.p02) and 2 matures ( IEBR-EW.174.p02), natural forests (10°24’22”N; 107°16’18”E), 33 m, Long Hai commune, Long Dien District, Ba Ria – Vung Tau Province, 25 October 2016, coll. Nguyen Phuc Hau.

Etymology. “ dorsomorrioides ”, an adjective, to emphasize the similarity to the species Amynthas dorsomorrisi .

Diagnosis. Small size, length 59–95 mm, diameter 2.5–3.1 mm, segments 135–151. Prostomium epilobous. First dorsal pore in 12/13. Setal numbers: 62–64 in viii, 54–57 in xxx, 6–7 between male porophores in xviii. Two pairs of spermathecal pores located dorsally in intersegments 5/6/7. Ventral distance between two male pores about 0.3x body circumference. A pair of pre-setal genital markings present in xvii. Intestinal caeca simple. Holandric. Testis sacs separated. Septa 8/9/10 absent.

Description. Cylindrical body, small size, length 59–95 mm, diameter 2.5–3.1 mm, weight 0.2–0.42 gr, segments 135–151. Body transparent, clitellum light brown. Prostomium 1/2 epilobous. First dorsal pore in 12/13. Setae perichaetine, pre-clitellar setae stouter and denser than post-clitellar ones; setal number: 62–64 in viii, 54–57 in xxx, 6–7 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.

Two pairs of spermathecal pores located dorsally in intersegments 5/6/7. No genital markings in spermathecal region. Male porophores ventrally located in setal ring of xviii; ventral distance between male pores about 0.3x body circumference. A pair of large, round genital markings ventrally present in front of setal ring xvii. These markings slightly larger than the male porophores and shifted mediad with respect to the male porophores.

Septa 5/6/7/8 thick, 8/9/10 absent, 10/11/12/13 thin. Oesophageal gizzard within viii–x. Intestinal origin at xiv; caeca simple, originating at xxvii and extending anteriorly to xxiv. Last hearts in xiii. Pharyngeal micronephridia developed 4/5/6. Typhlosole folded. Lymph glands absent.

Two pairs of spermathecae in vi and vii. Ampulla oval-shaped; ducts about 1/3 ampulla length. Diverticula shorter than ampulla, slightly waved, and directly attached to base of ampulla duct; seminal chamber small ovalshaped. No accessory glands.

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–xix; ducts transparent, C-shaped. A pair of accessory glands in association with genital markings in xvii.

Habitat. The species was found in sandy or clay-sandy soils at a depth of 0–10cm.

Remarks. The new species can be assigned to the Amynthas morrisi species group due to the presence of two pairs of spermathecal pores in 5/6/7 ( Sims & Easton 1972). To date, the A. morrisi group comprises 47 species, of which 13 species 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 similar to A. dorsomorrisi ( Do & Tran, 1995) in the absence of genital markings in the spermathecal region, simple intestinal caeca and a similar body size. Both species can be distinguished as follows: The new species has spermathecal pores located at some distance from the dorsal line (they are actually in dorsolateral position), a pre-setal pair of large round or oval genital markings in xvii, first dorsal pore in 12/13, about 6–7 setae between the male porophores, intestinal origin at xiv, and a folded typhlosole. In contrast, A. dorsomorrisi has spermathecal pores located closely to the dorsal line, one pair of small genital markings located behind the male pores in xviii, first dorsal pore in 11/12, no setae between two male porophores, intestinal origin at xv, and no typhlosole ( Do et al. 1995). In addition, the new species has 135–151 segments, transparent coloration and thinner body wall, whereas A. dorsomorrisi has 91 segments, light grey coloration and thicker body wall ( Do et al. 1995).

The new species shares the character state of dorsal spermathecal pores with several other Amynthas species outside the A. morrisi -group, such as, A. acidophilus ( Chen, 1946) , A. banaensis ( Pham, 1995) , A. binhgiaensis (Le, 1994) (in Do et al. 1994) , A. multichaetiferus ( Le, 1995) , A. ophthalmopapillatus ( Thai, 1982) and A. rodericensis ( Grube, 1879) . However, the new species is distinguished from these species by having two pair of spermathecal pores in 5/6/7 while A. banaensis and A. ophthalmopapillatus has one pair of pores in 5/6; A. acidophilus has two pairs in 6/7/8; A. arrobustus and A. multichaetiferus has two pairs in 7/8/9; A. binhgiaensis has three pairs in 5/6/7/8, lastly A. rodericensis four pairs in 5/6/7/8/9. In addition, Amynthas dorsomorrioides sp. nov. also differs from these species (but not from A. banaensis ) in having a pre-setal pair of large round or oval genital markings in xvii. These species except A. banaensis have genital markings paired in xviii or paired in 17/18 and 18/19 ( A. binhgiaensis ). The new species shares the character states of one pair of genital markings in xvii and first dorsal pore in 12/13 but they are clearly distinguished by genital markings in the spermathecal region (absent in A. dorsomorrioides sp. nov. vs. two pairs in vi and vii in A. banaensis ).

Regarding the arrangement of genital markings in the male region, the new species is fairly similar to A. wui ( Chen, 1935) and A. adexilis (Thai, 1984) by having only one pair in xvii; further similarities include epilobous prostomium, holandry, simple intestinal caeca, and absence of septa 8/9/10. However, these species can be distinguished by position and number of spermathecal pores (laterodorsally 5/6/ 7 in A. dorsomorrioides sp. nov. vs. lateroventrally 5/ 6 in A. wui , lateroventrally 5/6/7/8 or 5/6/7/8/ 9 in A. adexilis ), status of male sexual system and intestinal origin (separated testis sacs and xiv in the new species vs. connected testis sacs and xv or xvi in these three species, respectively).

Figures

FIGURE 3. Amynthas dorsomorrioides sp. nov. Holotype (CTU-EW.174.h01). A. Male region, ventral view. B. Testis sacs and seminal vesicle. C. Left prostate gland. D. Spermathecal region, dorsal view. E. Left intestinal caecum. F. Left spermatheca. G. Spermathecae (comp. F). H. Male region (comp. A). I. Prostate gland (comp. C). J. Intestinal caecum (comp. E). Scale bar = 1 mm.