Gianius inermis Sambugar & Martínez-Ansemil, 2025

Gianius inermis Sambugar & Martínez-Ansemil sp. nov.

( Figs 3 View FIGURE 3 , 4 View FIGURE 4 )

Holotype. MHNUSC_10149: mature worm, incomplete (broken at segment XVI), stained in paracarmine and whole-mounted in Canada balsam. Leg. Fabio Stoch.

Type locality. LES050 About LES Bus delle Piatte cave (441 V / VR) , Rocca , Lessinian Massif, Italy, 10.98458, 45.61771 ( 20 June 2006) GoogleMaps .

Paratypes. MHNUSC_10150_1: 1 mature specimen stained in paracarmine and whole mounted in Canada balsam, from type locality ( 20 June 2006) . MHNUSC_10150_2: 1 mature specimen stained in paracarmine and whole-mounted in Canada balsam, LES107 About LES Regosse cave (161 V / VR), Regosse, Lessinian Massif, 11.04847, 45.60577 ( 22 August 2001) GoogleMaps ; MHNUSC_10150_3: 1 mature specimen stained in haematoxylin and whole-mounted in Canada balsam, LES036 About LES Fumane-Molina interstitial, Lessinian Massif, 10.91867, 45.61550 ( August 2001) GoogleMaps ; MHNUSC_10150_4: 1 mature specimen stained in haematoxylin and whole-mounted in Canada balsam, LES124 About LES Verona–Montorio via del Lanificio interstitial, Lessinian Massif, 11.06650, 45.45950 ( August 2001) GoogleMaps . Leg. Fabio Stoch and Diana Galassi.

Etymology. The specific name refers to the lack of penial setae (Latin inermis , unarmed).

Description. Mature worms up to 5 mm long. Number of segments 28–33. Diameter at segment V (slightly compressed specimens) 105–135 μm, at segment XI 100–160 μm. Clitellum 1/2 X–XII. Prostomium rounded, 45– 65 μm long and 60–82 μm wide. Secondary annulation unnoticeable or slightly marked, up to V. Somatic setae bifid, 30–45 μm long, with upper tooth shorter and thinner than lower ( Fig. 4A View FIGURE 4 ); (2)3–4 somatic setae per bundle anteriorly and 2(3) in the clitellar and postclitellar segments (ventral setae absent in XI). Penial setae absent. One pair of male pores located in the posterior third of segment XI, in line with somatic ventral setae. One pair of spermathecal pores in segment X, placed in the most anterior part of the segment, in line with somatic ventral setae.

Pharyngeal glands in segments IV–VI. Chloragogen cells beginning in VI. Oesophageal appendages and diverticula absent. One pair of testes in segment X. One pair of ovaries in segment XI. Sperm sacs extending by segments X–1/2XII. Egg sac extending to 13/14. Vasa deferentia about as long as atria, around 5 μm wide, entering the apical end of the atria. ( Figs 3A View FIGURE 3 , 4C View FIGURE 4 [vd]). Atria tubular and curved, 115–140 μm long and 13–20 μm maximum diameter, with a thin muscular outer layer (1–2 μm thick); atrial lumen frequently containing spermatozoids; ectally, the atrium ends directly in a simple pore, surrounded by muscular strands, and can extrude somewhat as a small pseudopenis ( Figs 3A View FIGURE 3 , 4E View FIGURE 4 [mp, ms]). Two roundish compact prostate glands per atrium, similar in size, the anterior one placed near the entrance of vas deferens, and the posterior one near the ectal end ( Figs 3A View FIGURE 3 , 4B–C View FIGURE 4 ). Spermathecae composed by a short conical muscular duct (13–20 μm long) dilated in a roundish vestibulum (16–30 μm in diameter) and followed by a long tubular ampulla (90–110 µm long, 13–22 µm wide) generally directed backwards in the segment ( Figs 3B View FIGURE 3 , 4D View FIGURE 4 ).

Distribution and habitat. Caves and interstitial habitats in the western and southern parts of the Lessinian Massif (Progno di Fumane basin, Progno di Valpantena basin and Vaio di Squaranto basin), southernmost part of the Venetian pre-Alps, Italy. Alt. 71– 700 m.

Remarks. Following Erséus (1992a), the presence of elongated and curved atria, each with two prostate glands attached to proximal and distal ends, respectively, vasa deferentia entering apical ends of atria, slender spermathecae with short ducts, and small straight penial setae allocate the new species described above in the genus Gianius Erséus.

The species most closed relative to Gianius inermis sp. nov. appears to be G. labouichensis ( Rodriguez & Giani, 1989) , described from the underground stream of Labouiche (Ariège, France). G. labouichensis is the only species of Gianius known until now with somatic setae in the ventral bundles of XI at maturity, instead of differentiated penial setae; the mature specimens of G. inermis sp. nov. are completely devoid of ventral setae in XI. The male ducts of G. labouichensis and G. inermis sp. nov. are similar in shape, but clearly smaller in the former (87 μm long, 7.5 μm in diameter). The location of the male pores in about the middle of the segment in G. labouichensis and in the posterior third of the segment in G. inermis sp. nov., and the absence in G. inermis sp. nov. of a dorsal appendage in the gut, present in G. labouichensis , are two other characters that clearly separate these two species.