Amynthas arenulus Bantaowong & Panha, 2014

Bantaowong, Ueangfa, Somniyam, Pattana, Sutcharit, Chirasak, James, Samuel W & Panha, Somsak, 2014, Four new species of the earthworm genus Amynthas Kinberg, 1867, with redescription of the type species (Clitellata: Megascolecidae), Raffles Bulletin of Zoology 62, pp. 655-670 : 658-660

Amynthas arenulus Bantaowong & Panha , new species

( Figs. 3 , 11A, B , 12 ; Table 1)

Material examined. Holotype: One semi-clitellate ( CUMZ 3299 ) Ban Khok Pho, Prasat, Surin, Thailand, (14°33ʹ5.33ʺN, 103°22ʹ21.79ʺE), 172 m in elevation, coll. S. Panha, U. Bantaowong, C. Sutcharit, R. Chanabun & W. Siriwut, 15 October 2012. 16 paratypes: 10 adults ( CUMZ 3300 ), 2 adults ( ZMH), 2 adults ( NHMUK), and 2 adults ( ZRC), same collection data as for holotype.

Other material examined. 2 adults ( CUMZ 3301 ), Khao Sala Temple , Buachet, Surin, Thailand, (14°25ʹ9.7ʺN, 103°56ʹ0.7ʺE), 340 m in elevation, 16 October 2012 . 3 adults and 1 juvenile ( CUMZ 3302 ), paddy field in Nam Yuen , Ubon Ratchathani (road no. 2248, about 18 km from Kantharalak, Sisaket), Thailand, (14°28ʹ10.1ʺN, 104°52ʹ33.2ʺE), 191 m in elevation, 17 October 2012 . 5 adults ( CUMZ 3303 ), Kaeng Lam Duan Waterfall , Nam Yuen, Ubon Ratchathani, Thailand, (14°26ʹ6.2ʺN, 105°06ʹ17.0ʺE), 164 m in elevation, 17 October 2012 .

Diagnosis. Large; length 267–465 mm. Male pores paired, superficial in segment XVIII, each on large transversely elliptical disc, male aperture inconspicuous, genital markings absent. Spermathecal pores paired in segments 6/7–8/9. Spermathecae large bulb-shaped ampulla, small tube-like diverticulum adherent to ampulla on its entire length. Holandric, intestinal caeca simple, first dorsal pore in 12/13. Prostate glands large, its duct flanked by large sessile glandular masses on body wall.

Description of holotype. Dimensions; 465 mm by 13.3 mm at segment VII, 15.7 mm at segment XX, 14.5 mm at clitellum; body cylindrical with 176 segments. Setae regularly distributed around segmental equators, numbering 68 at VII, 101 at XX, 26 between male pores, setae formula AA:AB:ZZ:ZY=1:1:2:1 at XIII. Single female pore at XIV. Prostomium epilobic. First dorsal pore at 12/13. Clitellum annular XIV–XVI with setae.

A pair of male pores located ventro-laterally in XVIII, 0.41 circumference apart ventrally, distance between male pores 18 mm, porophores large transversely elliptical discs, surrounded by elevated rim. The indistinct male apertures located at the outer edges of each porophore. No genital markings are observed. Three pairs spermathecal pores, transverse slits, in furrows 6/7–8/9, ventral, distance between each pair about 0.38 body circumference ventrally apart, distance between spermathecal pores 15 mm. No genital markings in the spermathecal pore area.

Septa 5/6–7/8 thick, 8/9–9/10 absent, 10/11–11/12 thin. Gizzard large behind 7/8, intestinal origin XV; the intestinal caeca originate in XXVII, are simple and bend to XXIII. Typhlosole simple fold one–fourth lumen diameter, begins in XXVII. Oesophageal hearts four pairs in X–XIII. Holandric; testes and funnels in X and XI. Seminal vesicles paired in XI–XII, are large. Prostate glands well developed, large, extending anteriorly to segment XVII, posteriorly to XXII. Prostate duct flanked by large sessile glandular masses on body wall.

Ovaries in XIII. Three pairs spermathecae in VII–IX. Ampulla large sac–shape, duct relatively stout, diverticulum adherent to duct and ampulla on its entire length, slender with a thin stalk, chamber a dilated, elongate bulb.

Variation. The holotype measures 465 mm body length with 176 segments; the 16 paratypes range in size from 267–340 mm (±26.62) body length with 133–169 segments.

Etymology. The specific epithet is from the Latin for a sandy place. This refers to the find-grained sandy area modified as a highland rice paddy system, which is the habitat of the new species.

Distribution. Surin, Sisaket and Ubon Ratchathani.

Habitat. The species lives in the sandy top soil at about 20–30 cm depth, in a highland paddy system modified from dipterocarp forest. Some forest patches are still present near the paddy fields.

Remarks. Amynthas arenulus , new species, is sexthecal with spermathecal pores in 6/7–8/9. The Amynthas species with these characters were formerly classified in the sieboldi species group ( Sims & Easton, 1972); however, Easton (1981) transferred A. sieboldi ( Horst, 1883) to the genus Metaphire , so the species group name is no longer appropriate. Thus James et al. (2005) have critically investigated and proposed the aelianus species group after A. aelianus ( Rosa, 1892) , to replace the sieboldi species group name. This is one of many modifications of the group names of Sims & Easton (1972); among those are the use of confirmed senior synonyms corticis species group (replacing diffringens) and gracilis species group (replacing hawayanus).

The aelianus species group consists of more than 50 species and also included nine recently described species from Taiwan and one species from Thailand ( Sims & Easton, 1972; Tsai et al., 1999, 2010; Shen et al., 2003; James et al., 2005; Blakemore, 2011). In Thailand, only two species within this species group were reported from northeastern Thailand, A. fucosus ( Gates, 1933) and A. siam Blakemore, 2011 . However, A. arenulus , new species, is distinguished from the above related species in Thailand by the larger body with no genital markings while A. fucosus has two pairs of genital markings at 17/18, 18/19 and A. siam has single pair between the male pores.

Amynthas arenulus is also fairly similar to A. osmastoni ( Michaelsen, 1907) from Burma, and A. burchardi Michaelsen, 1899 , from Sumatra, in body size, but it is easily distinguished by having no genital markings, whereas the latter two species have genital markings. Moreover, the distance between the male pores as a fraction of the estimated circumference of segment XVIII is 0.25 and 0.28 in A. osmastoni and A. burchardi , respectively, while in A. arenulus , new species, this distance is 0.41 body circumference for the holotype. In addition, A. arenulus , new species, has unique spermathecae, the diverticulum being adherent to the duct-ampulla axis along its whole length, while in other Amyntha s species, the diverticulum is usually free of the duct and ampulla except at a single point of origin ( Table 1).

Figures

Fig. 3. External and internal morphology of holotype (CUMZ 3299) of Amynthas arenulus, new species: A, external ventral view; B, internal dorsal view; C, spermathecae. Dark arrow indicates the connection of the spermathecae and spermathecal pore.

Fig. 11. Photographs showing typical habitat types of the new species: A, B, Amynthas arenulus, new species. A, earthen dyke around paddy field; B, casting. C, D, Amynthas longicaeca, new species. C, dipterocarp forest; D, casting. E, F, Amynthas thakhantho, new species. E, organic gardening; F, tower–like casting.

Fig. 12. Photographs of Amynthas arenulus, new species.A, B, living specimen from the type locality showing the coloration; C, specimen from Sisaket, just after anesthesis step in 30% (v/v) ethanol showing the coloration of the ventral side.