Amynthas sakonnakhonensis Chanabun & Panha, sp. nov.

Chanabun, Ratmanee, Aoonkum, Anuwat, Seesamut, Teerapong, Bantaowong, Ueangfa & Panha, Somsak, 2023, Four new terrestrial earthworm species from the northeast Thailand (Oligochaeta, Megascolecidae), ZooKeys 1176, pp. 195-219 : 195

Amynthas sakonnakhonensis Chanabun & Panha, sp. nov.

Figs 5 , 6

Type material.

Holotype: Adult specimen (CUMZ 3823), Nong Tuet, Samakkee Pattana, Akat Amnuai, Sakon Nakhon, northeast of Thailand, 17°40'54.1"N, 103°59'50.6"E, 149 m a.m.s.l., 6 October 2019, coll. R. Chanabun, A. Aoonkum. Paratypes: 25 adults (CUMZ 3824), 2 adults (NHMUK), 2 adults (ZMH), same collection data as for holotype.

Diagnosis.

Medium-large size, length 134-238 mm, diameter 6-9 mm, 85-162 segments. Male pores paired in segment XVIII, each surrounded by four genital markings. Paired spermathecal pores in intersegments 6/7-8/9. Spermathecae large oval sacs of the ampulla, with stout and short duct, it is less than ampullar in length. Diverticulum long and zigzagged at the beginning and dilated towards the distal end, a baton-like chamber. Intestinal origin at XV. Intestinal caeca simple. Holandric. First dorsal pore in 12/13. Prostate glands large in segments XV-XXII, its ducts long and slender, surrounded by a large, long sessile glandular mass on the body wall.

Description of holotype.

Length 217 mm, diameter 9 mm, body cylindrical with 156 segments. Preserved specimens are dark brownish on the dorsal part and pale gray on the ventral part. Setae regularly distributed around the segmental equators, numbering 49 at segment VII, 72 at segment XX, and 10 between male pores at segment XVIII. Setal formula is AA:AB:ZZ:ZY = 1:1:2:1 at XIII. Single female pore on the ventral side at segment XIV. Prostomium epilobic. First dorsal pore in 12/13. Clitellum annular in XIV-XVI with no dorsal pores or setae.

Male pores paired on the ventral side at XVIII, in a setal line ~ 5 mm and 0.18 × the circumference apart ventrally. Male pores superficial, convex, and surrounded by four genital markings each. Large spermathecal pores three pairs in 6/7-8/9. The distance between each pair ~ 0.27 × the circumference ventrally apart, with no genital markings on this area.

The septa at 5/6-7/8 thick, absent in 8/9-9/10, slightly thick in 10/11-11/12, thin in 12/13-14/15, and very thin behind 15/16. Gizzard large in IX-X. Intestine begins in segment XV. Long and simple intestinal caeca in XXVII-XXII. Esophageal hearts four pairs in segment X-XIII. Holandric; testes and funnels in X and XI. Seminal vesicles are paired, one in XI, the other one in XII-XIII. The prostate glands are well developed, located in XV-XXII, and divided into several lobules. The prostate duct is long and slender, surrounded by a large, long sessile glandular mass on the body wall on segments XVII-XIX.

Ovaries located in segment XIII. Three pairs of spermathecae present on VII-IX. Spermathecae large oval sacs of the ampulla, with stout and short duct, it is less than ampullar in length. Diverticulum long and zigzagged at the beginning and dilated towards the distal end, a baton-like chamber.

Variation.

Twenty-nine paratypes range in body length from 134-238 mm (197.33 ± 24.52 mm), with 85-162 (142.96 ± 21.25) segments (Table 2 ).

Etymology.

The name sakonnakhonensis was derived from the province Sakon Nakhon.

Distribution.

This species is known only from the type locality.

Remarks.

Amynthas sakonnakhonensis sp. nov. is sexthecal with spermathecal pores in 6/7-8/9. This species keyed to the Amynthas sieboldi species group ( Sims and Easton 1972). After that, Easton (1981) moved A. sieboldi (Horst, 1883) to the genus Metaphire . Then James et al. (2005) investigated and proposed the Amynthas aelianus species group after A. aelianus (Rosa, 1892), to replace the Amynthas sieboldi species group name ( James et al. 2005; Bantaowong et al. 2014).

The Amynthas aelianus species group consists of more than 60 species ( Sims and Easton 1972; Tsai et al. 1999, 2010; Shen et al. 2003; James et al. 2005; Blakemore 2011; Bantaowong et al. 2014). In the following, we compared the new species with regional species in the Amynthas aelianus species group: A. osmastoni (Michaelsen, 1907) from Myanmar, A. burchardi Michaelsen, 1899 from Sumatra, A. monsoonus James, Shih & Chang, 2005 and A. huangi James, Shih & Chang, 2005 from Taiwan ( James et al. 2005).

Amynthas sakonnakhonensis sp. nov. is similar to A. osmastoni from Myanmar and A. burchardi from Sumatra in the body size, but its easily distinguished by the new species having no median genital markings on segment VIII while A. osmastoni has them, the new species having no mid-ventral group of small circular papillae on segment XVIII while A. burchardi has them. Amynthas sakonnakhonensis sp. nov. can be distinguished from A. monsoonus and A. huangi from Taiwan in that the new species has a larger body size than these two species, A. monsoonus has genital markings in segments VII-IX. Amynthas monsoonus and A. huangi have no genital markings in the male pores region, whereas the new species contains these characters.

In Thailand, only four species within this species group have been reported from northeastern Thailand. These are A. fucosus (Gates, 1933), A. siam Blakemore, 2011, A. arenulus Bantaowong & Panha, 2014, A. longicaeca Bantaowong & Panha, 2014. Amynthas sakonnakhonensis sp. nov. is easily distinguished from A. fucosus from Burma and A. siam from Thailand because these species have body diameters of 6 mm and 3 mm, respectively, while the new species are wider at ~ 8-10 mm. Amynthas fucosus has two pairs of genital markings at 17/18 and 18/19, and A. siam has a single pair between the male pores, while the new species has four genital markings surrounded by male pores. This new species differs from A. arenulus in that the latter has a larger size and lacks genital markings in the male pore area. Amynthas arenulus has a large transverse elliptical disc surrounded by an elevated rim with an indistinct male aperture located at the outer edge of each poropore, while the new species has four genital markings surrounding the male pore area. The new species has body dimensions similar to A. longicaeca but can be distinguished from A. longicaeca by the fact that A. longicaeca has small crescent-shaped genital markings in the male pore region and spermathecae consist of large oval ampullar with short duct, diverticulum has a small ovate knob and nephridia are present on diverticulum, while the new species has none of these characters.

Amynthas sakonnakhonensis sp. nov. is similar to A. bantanensis sp. nov. in body size but can be distinguished by the A. sakonnakhonensis sp. nov. having large oval sacs of the ampulla, with stout and short duct, with long and zigzag diverticulum, and has large, long sessile glandular mass on the body wall region of XVII-XIX, as opposed to A. bantanensis sp. nov., which has elongated sacs of the ampulla with slender and long stalks, and has no such glandular mass. Amynthas sakonnakhonensis sp. nov. differs from A. auriculus sp. nov. by the latter has a bit larger size, male pores located in between small three genital markings, each male pore region somewhat ear-shaped after fixation, and consists of a large, elongated ampullar with very short and zigzag diverticulum; however, A. sakonnakhonensis sp. nov. has four genital markings surrounding the male pore area, and has a large oval sacs of the ampulla, with long and zigzag diverticulum. Amynthas sakonnakhonensis sp. nov. different genital marking pattern from the other new Amynthas species here, and the other related species is presented in Table 5 .

Figures

Figure 5. Photographs showing the A type locality of Amynthas sakonnakhonensis sp. nov. from Nong Tuet, Samakkee Pattana, Akat Amnuai, Sakon Nakhon, Thailand B living specimen under the stone near casts C coloration of a living paratype, and D coloration of a newly collected paratype (CUMZ 3824) after the first preservation step in 30 % (v / v) ethanol.

Figure 6. External and internal morphology of Amynthas sakonnakhonensis sp. nov., holotype (CUMZ 3823) A external ventral view B internal dorsal view, and C spermatheca with location of spermathecal pore arrowed.