Amynthas phuquocensis, Nguyen & Lam & Trinh & Nguyen, 2020

Nguyen, Tung T., Lam, Dang H., Trinh, Binh T. K. & Nguyen, Anh D., 2020, The megascolecid earthworms (Annelida, Oligochaeta, Megascolecidae) in the Phu Quoc island, Vietnam, with descriptions of three new species, ZooKeys 932, pp. 1-25 : 1

Amynthas phuquocensis sp. nov. Figs 12 , 13 , Tables 2, 3

Material examined.

Holotype: 1 mature (CTU-EW.188.h01), Kien Giang Province, Phu Quoc island, natural forests (10°20'51.3"N, 103°58'58.0"E), 44.2 m, 7 November 2016, coll. Lam HD & Trinh TKB.

Paratypes: 9 matures (CTU-EW.188.p02) same data as for holotype.

Non-types: 9 matures (CTU-EW.188.03) same data as for holotype; 4 matures (CTU-EW.188.04), Kien Giang Province, Phu Quoc island, natural forests (10°20'50"N, 103°55'07"E), 57 m, 7 November 2016, coll. Lam HD & Trinh TKB.

Diagnosis.

Medium-sized, length 74-145 mm, average diameter 2.5-4.7 mm, segments 116-145. Prostomium epilobous. Two pairs of spermathecal pores in ventral intersegments 7/8/9. Male pores in xviii, without copulatory pouches. Two pairs of genital markings present in ventral 17/18 and 18/19. Intestinal caeca simple. Holandric. Testis sacs in xi, separated. Septa 8/9/10/11 absent.

Etymology.

" phuquocensis ", named for the type locality.

Description.

Body cylindrical, medium size, length 74-145 mm, average diameter 2.5-4.7 mm, segments 116-145, weight 0.6-3.7 g. Body uniformly greyish brown except darkish brown clitellum. Prostomium 2/3 epilobous. First dorsal pore in 12/13. Pre-clitellum setae stouter and sparser than post-clitellum ones; setal numbers: 42-61 in viii, 50-77 in xxx, 5-9 between male porophores in xviii; setal distance: aa> ab, zz> zy. Clitellum within xiv-xvi, without setae and dorsal pores. Female pore single, in mid-ventral xiv.

Two pairs of spermathecal pores in ventral intersegments 7/8/9. Genital markings absent in the spermathecal region. Male pores located in the setal ring xviii, without copulatory pouches; ventral distance between two male pores about 0.28 × body circumference. Genital markings roundly pad-shaped and variable in the male region, normally with two pairs in 17/18 and 18/19, or a pair in xix (near 19/20).

Septa 5/6/7/8 thick, 8/9/10/11 absent, 11/12/13 thick. Oesophageal gizzard within viii-xi. Intestinal origin at xv. Intestinal caeca simple, within xxvii-xxiv. Last hearts in xiii. Pharyngeal micronephridia in 5/6/7. Typhlosole lamelliform. Lymph lobuled, from 15/16.

Two pairs of spermathecae in viii and ix. Ampulla large, heart-shaped with transverse wrinkles; ducts short and stout. Diverticula waved, attached to the base of ampulla; seminal chamber ellipsoid. Accessory glands bean-shaped, surrounding spermathecal ducts.

Holandric. Testis sacs in xi, separated, the anterior pair poorly developed. Seminal vesicles well developed in xi and xii. Ovaries in 12/13. Ovisacs invisible. Prostate glands deeply lobuled in xvi-xx; ducts strongly coiled. Accessory glands present.

Habitats.

The species was occasionally found in natural forests along the main road to the northern part of Phu Quoc island. They were collected in the upper soil layer (0-10cm).

Vietnamese name.

Giun phú quốc.

Variations.

The body size and number of genital markings in the male region are variable among collected specimens. Specimens can be divided into two groups based on body size. The group of smaller specimens (n = 15) present the following ranges: length = 71-85 mm, diameter = 2.5-2.9 mm, segments = 116-145. The larger specimens (n = 8) present: length = 96-145 mm, diameter = 3.1-4.7 mm, segments = 124-145. Both two groups were together at the same site.

Genital markings are also variable in the male region. Genital markings have two pairs located in 17/18 and 18/19 (Type 1), but reduced to three genital markings (Type 2), one pair either in xvii or in xiv (Type 3 or Type 4), or a single one in xix (Type 5) (Fig. 12 ).

Remarks.

The new species can be assigned into the Amynthas aeruginosus group, which is characterized by having two pairs of spermathecal pores in 7/8/9 and holandric ( Sims and Easton 1972). This group is known to have about 70 species distributed mainly in Southeast and East Asia. Of these, about 11 species have been recorded in Vietnam ( Nguyen et al. 2016).

Within the A. aeruginosus group, the new species is fairly similar to A. phimpheti Hong, Inkavilay & James, 2018 and A. antethecus Hong, Inkavilay & James, 2018 in having two pairs of genital markings in the male region, but absent in the spermathecal region, and a simple intestinal caeca. However, these species can be distinguished by the positions of the first dorsal pore and the spermathecal pores and genital markings in the male region, the presence of septum 10/11, presence of accessory glands, and position of testis sacs (summarized in Table 2 ).

Regarding the arrangement of genital markings in the male region, the new species is slightly similar to A. platycorpus (Thai, 1982) and A. binhgiaensis (Le, 1994) by having two pairs of genital markings in 17/18 and 18/19. However, these species can be distinguished by number and position of spermathecal pores, first dorsal pore, genital markings in the spermathecal region, presence of septum 10/11, type of intestinal caeca and testis sacs (summarized in Table 3 ).

Figures

Figure 12. Variation of genital markings in the male region of A. phuquocensis sp. nov.

Figure 13. A. phuquocsensis sp. nov. Holotype (CTU-EW. 190. h 01) A 1, A 2 Male region, ventral view B 1, B 2 right spermathecae C 1, C 2 spermathecal region, ventral view D testis sacs and vesicles E intestinal caecum F 1, F 2 right prostatic gland G transection via male porophore H transection via genital marking. Scale bar: 1 mm.