Glossoscolex arnsi Dudas, Brown & Bartz, 2025

Glossoscolex arnsi Dudas, Brown & Bartz , sp. nov.

( Figures 2 View FIGURE 2 and 3 View FIGURE 3 )

Holotype. COFM BRRS0431 , adult individual, native vegetation, in 0–20 cm soil, by qualitative method, Vacaria , Rio Grande do Sul, Brazil, -28.391473, -51.082457, 879 m asl, August 18, 2023, M.L.C. Bartz coll. GoogleMaps

Paratype. COFM BRRS0425 , adult individual, native vegetation, in 0–20 cm soil, by qualitative method, Bom Jesus , Rio Grande do Sul, Brazil, -28.466743, -50.597859, 1003 m asl, 20 August 2023, M.L.C. Bartz coll. GoogleMaps

Other materials. COFM BRRS0530 , 41 individuals, same information as holotype. COFM BRRS531 , one adult , same information as paratype. COFM BRRS0415 , two adults , same information as paratype. COFM BRRS0419 , two adults , No-Tillage System , in 0–20 cm soil, by TSBF method, Bom Jesus , Rio Grande do Sul, Brazil -28.485754, -50.609524, 1043 m asl, 20 August 2023, G.C. Francisco, M.L.C. Bartz, N. Durães GoogleMaps , R. T. Dudas , R. Roani , T. Ferreira, W.C. Demetrio colls . COFM BRRS 0421 , 12 adults , No-Tillage System , in 0–20 cm soil, by qualitative method, Bom Jesus, Rio Grande do Sul, Brazil -28.485754, -50.609524, 1043 m asl, 20 August 2023, M.L.C. Bartz colls GoogleMaps . COFM BRRS0422 , 37 individuals, No-Tillage System , in 0–20 cm soil, by qualitative method, Bom Jesus, Rio Grande do Sul, Brazil -28.485754, -50.609524, 1043 m asl, 20 August 2023, M.L.C. Bartz and W.C. Demetrio colls GoogleMaps .

Etymology. The species is named in honor of the farmer Ulfried Arns and his family, owners of Três Marias Farm, pioneers of no-tillage system in Rio Grande do Sul state.

External morphology. Holotype: body length 59 mm after ethanol fixation. Body mass: 0.30 g fresh weight (alcohol preserved). Number of segments: 169. Diameter: 5 mm in the pre clitellar region (segment X), 6.3 mm in the clitellum (segment XVI) and 4 mm in the post clitellar region (segment XXX). Paratype: length 7.2 mm after ethanol fixation. Body mass: 0.34 g, number of segments: 159. Diameter: 3 mm in segment X, 4.3 mm in the clitellum at segment XVI and 2.9 mm in segment XXX. Body cylindrical, non-pigmented after fixation. Prostomium epilobic. Setae spacing uneven: aa and dd markedly larger than ab and cd, with bc intermediate. Setal arrangement aa:ab:bc:cd:dd, 3.0:1.1:2.3:1.0: 2.8 mm, measured on segment XXX. This pattern departs from the typical widely paired arrangement, so we describe it as nearly widely paired. Setae ab visible from V onwards, and cd on VIII. Clitellum in XIV to XXIII, saddle shaped. Genital marks or tubercula pubertatis absent. One pair of male pores, on B line setae, on a conical protuberance in XVII, 3.7 mm apart. Female pores not seen. Nephropores near B line.

Internal morphology. Septa strong, thickened on 7/8/9/10/11, strongly attached to the body wall, due thickness. Gizzard in VI, with average size (width x length) of 1.3 x 1.7 mm. One pair of calciferous glands in XII, composite-tubular type, with dorsal blood vessels. Intestine begins in XV with typhlosole also beginning in XV, lamellar form. Five pair of hearts, the last pair in XI, and dorsal blood vessels visible in segments VIII–X, above the calciferous glands. Nephridia tubular, elongated, slightly curved distally (J-shaped), without evident vesiculation, astomate starting before clitellum, in segments IX,X, close to the body wall and intestine, one pair per segment, aligned with C line. Unpaired testis sac, large, in XI, close to the calciferous gland. Seminal vesicles in XII, starting ventrally, below calciferous gland, and ending dorsally above the intestine on segment LX, lobular shaped stretching in two lines. Ovarian funnels and ovaries free in segment 13. Spermathecae absent. One pair of copulatory pouches (bulbs, chambers) with oval shape covering 1/3 XVI–1/3 XX, 3 mm long in the holotype.

Remarks. Currently the truncatus group has 34 described species ( Feijoo and Brown 2023, Dudas et al. 2025a,b), including the new species described here. Regarding the clitellum, Glossoscolex arnsi sp. nov. shares the extension and position (XIV–XIII) with G. bondari Michaelsen, 1926 , G. minor Zicsi & Csuzdi, 1999 , and G. tocape Righi, 1980 , although the first two have annular clitella, which differs from G. arnsi sp. nov. The primary distinctions between G. tocape and G. arnsi sp. nov. are the presence of ventrally fused testes sacs in XI in G. tocape , compared to the unpaired testis sac in the new species, and the presence of tubercula pubertatis (absent in the clitellum of G. arnsi sp. nov.) associated with the internal copulatory bulbs in segments XVI–XVIII in G. tocape (shorter than in G. arnsi sp. nov.). In G. arnsi sp. nov., the male pores are remarkably prominent for the body size, remaining conspicuous and easily observable from all perspectives, regardless of the worm’s orientation. A unique characteristic observed in G. arnsi sp. nov. is the position of the copulatory bulb, located from 1/3 XVI to 1/3 of XX, a feature not observed in other Glossoscolex species in the truncatus group (see table 2).