Sulawesidrobia lasoloensis, Kadow & von Rintelen & Iqram & Bichain & Haase, 2025

Sulawesidrobia lasoloensis sp. nov.

Etymology.

This species is named after the Lasolo River as it is the first description of a Sulawesidrobia occurring in the system of this river.

Material examined.

Holotype (Fig. 2 A View Figure 2 ): Indonesia • Sulawesi, North Konawe Regency, Amorome, northeast of Tambua, in a tributary of the Lasolo River . 3°25'35.6"S, 121°58'58.4"E. July 2010; Jean-Michel Bichain leg.; MZB Gst. 12193 . GoogleMaps

Paratypes (Fig. 3 A, B View Figure 3 ): Indonesia • N = 20; same collection data as for holotype; MZB Gst. 12194 GoogleMaps . N = 20; same collection data as for holotype; ZMB 118374 View Materials GoogleMaps . N = 10; same collection data as for holotype; MHNEC -MOLL 2025_04_001 GoogleMaps . N = 8; Sulawesi, North Konawe Regency, Amorome, northeast of Tambua, in a tributary of the Lasolo River . 3°25'43.1"S, 121°58'57.2"E. July 2010; Jean-Michel Bichain leg. MZB Gst. 12195 GoogleMaps . N = 7; same collection data, ZMB 118375 View Materials GoogleMaps .

Diagnosis.

This new species is characterized by the cylindro-conical shell shape, the anterodorsal insertion of the bursal duct in the ovoid bursa copulatrix, and the penis resting in U-shape with a swelling in the distal third on the left side and a small, round lobe on the right side behind the swelling.

Description.

Shell. Cylindro-conical to conical, slender, 1.7 to 2 times higher than wide, 3.5 to 4.125 whorls, sutures shallow, whorls moderately flat in profile, semitranslucent, goldish-brown, periostracum without color (Figs 2 A View Figure 2 , 3 A, B View Figure 3 ); protoconch (N = 4) wrinkled comprising 0.8–1 whorls (Fig. 4 A View Figure 4 ), teleoconch with growth lines, otherwise without structure; umbilicus a narrow slit; outer lip straight.

Operculum (N = 9). Light orange to yellow, thin, paucispiral, nucleus eccentric,

External features (N = 9). General appearance fairly light, black pigmentation rather sparse, but variable; eyes black, epidermal black pigment spots almost like eyebrows behind and toward the inner side of the eyes, tentacles otherwise white, proximal region of snout and head pigmented, mirrored, sickle-shaped spots on pharynx; mantle more or less loosely pigmented, almost unpigmented over distal genital glands in both sexes, upper parts of whorls darker than lower ones.

Mantle cavity (N = 8). Gill with 10–13 filaments almost abutting to pericard; osphradium ovate to elongate-ovate, about 1 / 3 of length of gill, rather behind middle of gill.

Digestive system (N = 3 for radula, 9 for rectum and stomach). Radula formula R: 4-5 1 4-5 / 2 - 3 2-3; L: 3-4 1 4-5, M 1: 16-22, M 2: 20-25; lateral tooth with membranous junction between face and flank (Fig. 5 View Figure 5 ); stomach without caecum, outer side brown to black; rectum makes a short loop in roof of mantle cavity underneath distal genital glands, more conspicuous in males than in females (Fig. 6 A – C View Figure 6 ).

Female genitalia (N = 5; Fig. 7 A-C View Figure 7 ). Ovary a simple sac, starting 1–1.5 whorls below apex, comprising 0.25 to almost 0.5 whorls, reaching stomach; renal oviduct with U-shaped loop followed by 270 ° - loop underneath ovoid bursa copulatrix lying largely behind albumen gland, bursal duct short emerging anterodorsally, no receptaculum seminis, sperm storage in distal part of second oviduct loop; albumen gland milky-white, capsule gland bipartite with a posterior opaque white and an anterior milky-white portion.

Male genitalia (N = 4). Testis lobate, starting 0.75 to 1.25 whorls below apex, comprising more than 1 whorl, reaching or overlapping proximal part of stomach; vesicula seminalis coiling underneath distal half of testis; penis in rest U-shaped, tip pointing forward, for most of the length with parallel sides, a swelling in the distal third on the left side and a small, round lobe on the right side behind the swelling (Fig. 8 A View Figure 8 ), penial base with black pigment.

Remarks.

The cylindro-conical form of this new species is rare among species of Sulawesidrobia and only seen in S. angusta Haase & Bouchet, 2006 from Lake Poso ( Haase and Bouchet 2006), which has a smaller aperture and less convex whorls, though. The shapes of bursa copulatrix and penis are unique. The morphological variation at the type locality was higher than in the other stream with the slender forms occurring only in the former (Fig. 9 View Figure 9 ). The broader form approaches S. marmer sp. nov. described below but differs through the smaller size, the less translucent shell, and the gold-brown color. Both species were well supported as sister species in the phylogenetic analyses. Their relationship to a clade of the Malili Lake system including S. abreui Zielske, Glaubrecht & Haase, 2011 , received moderate support (Figs 10 View Figure 10 , 11 View Figure 11 ).

This species is the only species from Sulawesi where a membranous junction between face and flank in the lateral radular teeth typical for the majority of Pacific tateids (e. g., Haase and Zielske 2015) has been observed so far.