Amynthas auriculus 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 auriculus Chanabun & Panha, sp. nov.

Figs 7 , 8

Type material.

Holotype: Adult specimen (CUMZ 3825) Wut Tham Kham, Phannanikom, Sakon Nakhon, northeast of Thailand, 17°13'06.2"N, 103°54'00.7"E, 403 m a.m.s.l., 9 October 2019, coll. R. Chanabun, A. Aoonkum. Paratypes: 2 adults (CUMZ 3826), 2 adults (NHMUK), same collection data as for holotype.

Diagnosis.

Medium-large size, length 184-267 mm, diameter 9-11 mm, 95-151 segments. Paired male pores at segment XVIII, surrounded by three genital papillae, each male pore region somewhat ear-shaped after fixation. Paired spermathecal pores in intersegments 6/7-8/9. Spermathecae are large, elongated sacs, with slender stalks of the ampulla, and diverticulum very short and zigzagged from its origin until the end. Holandric. Intestinal caeca simple. First dorsal pore in 12/13. Prostate glands large in XVI-XXIV, the prostate duct large, slender, smooth, and a bit zigzagged at the end, surrounded by a large sessile glandular mass on the body wall.

Description of the holotype.

Length 267 mm, diameter 10 mm, body cylindrical. 139 segments. Preserved specimens are dark brownish on the dorsal part and pale gray on the ventral part. Setae are regularly distributed around segmental equators, numbering 27 at segment VII, 62 at segment XX, and 20 between male pores at segment XVIII. Setal formula AA:AB:ZZ:ZY = 1:1:2:1 at XIII. At segment XIV, a single female pore mid-ventrally. Prostomium epilobic. First dorsal pore in 12/13. Clitellum annular in segments XIV-XVI with no dorsal pores or setae.

Male pores paired, superficial, convex, located on ventral side of segment XVIII, in between small genital markings; each male pore region somewhat ear-shaped after fixation in ethanol. Male pores ~ 7 mm apart, distance 0.29 × the body circumference. Single female pore at XIV. At segment XVIII, each male pore is lined by two anterior genital markings above the setal line, and one posterior genital marking below the setal line. Spermathecal pores three pairs in 6/7-8/9, distance between each pair is ~ 0.37 × the circumference ventrally, there are no genital markings in this area.

The septa are thick in 5/6-7/8; 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 at IX-X. Intestine begins at segment XV. Long and simple intestinal caeca in XXVII-XXI. Esophageal hearts four pairs in segment X-XIII. Holandric; testes and funnels in X and XI. Seminal vesicles paired in XI-XII. Prostate glands divided into several lobules, in XVI-XXIV, large and well-developed. Prostate duct large, slender, smooth, and a bit zigzagged, surrounded by a large sessile glandular mass on the body wall on segments XVIII-XXI.

Ovaries in segment XIII. Three pairs spermathecae in VII-IX. Spermathecae large, elongated sacs with slender stalks of the ampulla, diverticulum very short and zigzagged from its origin until the end.

Variation.

Four paratypes range in size from 184-224 mm (218.20 ± 30.80 mm) body length with 95-151 (128.40 ± 22.65) segments (Table 3 ).

Etymology.

The species was named after the region of the male pore that looks like an ear after being preserved.

Distribution.

This species is known only from the type locality.

Remarks.

Amynthas auriculus sp. nov. belongs to the Amynthas aelianus species group. This new species is quite similar to A. osmastoni from the South Andaman Islands and A. burchardi from Sumatra in the body dimensions but differs in having genital markings in the male pore area and having large sessile glandular masses on the body wall in XVIII-XXI, while A. osmastoni has genital markings in the spermathecal pores region without glandular masses on the body wall, and A. burchardi has a group of circular papillae in mid-ventral XVIII with no glandular masses on the body wall. Amynthas auriculus sp. nov. can be distinguished from A. monsoonus and A. huangi from Taiwan in which the new species has a larger body size, A. monsoonus has a body size of 102 mm, a diameter of 3.6 mm, with 83 segments and genital markings in segments VII-IX, while the new species is absent. Amynthas huangi has a body size of 70 mm, a diameter of 3.5 mm, with 101 segments, and genital marking glands in the body wall in VI-IX, while the new species has no such character. Amynthas monsoonus and A. huangi have no genital markings in the male pores region, whereas the new species is present.

Amynthas auriculus sp. nov. is easily distinguished from the other four earthworms of the Amynthas aelianus species group reported from Thailand, namely A. fucosus from Myanmar, A. siam from Thailand, by its size and other physical traits. Amynthas fucosus has a body size range of 120 mm with a diameter of 6 mm and 114 segments, A. siam has a body size range of 73 mm, diameter of 3 mm, while the new species has a body size that ranges from 184-267 mm with a diameter of 9-11 mm, and 95-151 segments. Amynthas fucosus has two pairs of genital markings at 17/18, 18/19, and A. siam has single pair between the male pores, while the new species has three genital markings in the male pores. This new species differs from A. arenulus in that A. arenulus has no genital markings. In contrast, the new species has them at segment XVIII, near the male pores area. The new species is relatively similar to A. longicaeca in body size; however, A. longicaeca differs in that it has an oval ampulla, a small ovate knob with nephridia on the diverticulum, and also has a crescent-shaped male pore region (Table 5 ).

Figures

Figure 7. Photographs showing the A type locality of Amynthas auriculus sp. nov. from Wut Tham Kham, Phannanikom, Sakon Nakhon, Thailand B casts of the new species C coloration of a living paratype, and D coloration of a newly collected paratype (CUMZ 3826) after the first preservation step in 30 % (v / v) ethanol.

Figure 8. External and internal morphology of Amynthas auriculus sp. nov., holotype (CUMZ 3825) A external ventral view B internal dorsal view, and C spermatheca with location of spermathecal pore arrowed.