Amynthas catenatus, 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 catenatus sp. nov. Fig. 11 , Table 1

Material examined.

Holotype: 1 mature (CTU-EW.189.h01), Kien Giang Province, Phu Quoc island, industrial tree plantations (10°06'11"N, 104°00'51"E), 20 m, 6 November 2016, coll. Lam HD & Trinh TKB.

Paratypes: 9 matures (CTU-EW.189.p02), same data as for holotype.

Non-types: 8 matures (CTU-EW.189.03), same data as for holotype.

Diagnosis.

Small to medium-sized, length 51-54 mm, diameter 2.2-2.5 mm, segments 85-89. Prostomium epilobous. Four pairs of spermathecal pores in lateroventral intersegments 5/6/7/8/9. Male pores in xviii, without copulatory pouches. Genital markings arranged in two transverse line in front of and behind the setal ring xviii. Intestinal caeca simple. Holandric. Testis sacs in xi and xii, separated. Septa 8/9/10 absent.

Etymology.

" catenatus ", an adjective in apposition, to emphasize the chained seminal chamber of diverticula.

Description.

Body cylindrical, small to medium-sized, length 51-54 mm, diameter 2.2-2.5 mm, segments 85-89, weight 1.2-1.4 g. Body uniformly whitish grey, clitellum darkish brown. Prostomium 1/2 epilobous. First dorsal pore in 5/6. Pre-clitellum setae stouter and sparser than post-clitellum setae; setal numbers: 47-54 in viii, 46-48 in xxx, no setae between two male porophores; setal distance: aa> ab, zz> zy. Clitellum within xiv-xvi, slightly flattened ventrally, without setae and dorsal pores. Female pore single, in mid-ventral xiv.

Four pairs of spermathecal pores in lateroventral intersegments 5/6/7/8/9. No genital markings in the spermathecal region.

Male porophores small in xviii, without copulatory pouches; ventral distance between two male pores about 0.25-0.28 × body circumference. About 8-12 small genital markings ventrally arranged in two transverse lines in front of and behind the setal ring xviii.

Septa 5/6/7/8 thick, 8/9/10 absent, 10/11/12 thick. Oesophageal gizzard within viii-x. Intestinal origin at xv. Intestinal caeca simple, within xxvii-xxvi. Last hearts in xiii. Pharyngeal micronephridia in 5/6/7. Typhlosole lamelliform. Lymph glands absent.

Spermathecae paired in vi-ix. Ampulla clavate; ducts not clearly distinct from ampulla. Diverticula slightly waved, attached to the base of ampulla; seminal chamber small, chained-shaped with 2 or 3 parts. No accessory glands.

Holandric. Testis sacs in x and xi, connected. Seminal vesicles well developed in xi and xii. Ovaries in 12/13. Ovisacs invisible. Prostate glands deeply lobuled within xvi-xx; ducts U-shaped. No accessory glands.

Habitats.

The species was only collected under leaf litter in Piper plantations.

Vietnamese name.

Giun buồng tinh hình chuỗi.

Remarks.

The new species can be assigned to the A. corticis group, which is characterized by having four pairs of spermathecal pores in 5/6/7/8/9 and holandric ( Sims and Easton 1972). This group has 108 described species worldwide, of which 17 have been recorded in Vietnam ( Gates 1972; Sims and Easton 1972; Chang et al. 2009; Nguyen et al. 2016; Xiao 2019).

Compared to A. corticis (Kinberg, 1867), the new species differs in its smaller size (length 51-54 mm, diameter 2.2-2.5 mm vs length 45-170 mm, diameter 3.0-6.0 mm), first dorsal pore in 5/6 (vs in 11/12), and absence of pre-clitellar genital markings (vs genital markings paired near spermathecal pores). In addition, A. catenatus sp. nov. has 8-12 small genital markings ventrally arranged in two transverse lines in presetal and postsetal xviii, a clavate spermathecal ampulla, slightly wavy diverticula and attached to the base of ampulla, and a small seminal chamber, which is chained-shaped with 2 or 3 parts. On the contrary, A. corticis has two pairs of small circular genital markings located next to male pores in presetal and postsetal xviii, an ovoid ampulla, and a blunt, ovoid diverticula with straight stalk.

Within the A. corticis group, Amynthas catenatus sp. nov. is fairly similar to A. divitopapillatus (Thai, 1984) and A. conhanungensis (Thai, 1984) in having numerous genital markings in xviii and spermathecal pores in 5/6/7/8/9. However, they are differentiated in the position of first dorsal pore, number and arrangement of genital markings in the male region, presence of septum 8/9, type of intestinal caeca, and body size (summarized in Table 1 ).

Figures

Figure 11. Amynthas catenatus sp. nov. Holotype CTU-EW. 184. h 01 A 1, A 2 Male region, ventral view B 1, B 2 left prostatic gland C spermathecal region, ventral view D 1, D 2 left spermathecae D testis sacs and vesicles F 1, F 2 intestinal caecum G transection via male porophore H transection via genital marking. Scale bar: 1 mm.