Sulawesidrobia carsonae Haase & Rintelen & Harting & Marwoto & Glaubrecht 2023, sp. nov.

Sulawesidrobia carsonae sp. nov.

urn:lsid:zoobank.org:act: 1E37CB23-9233-4A75-810F-C6109B54C098

Figs 2B, 3C–D, 4A–B, 5B, 6D, 7C–D, 8C–D

The new species has a small, short-conical shell with a unique protoconch structure where the fine pits are distally rearranged as irregular longitudinal striae. It is the only short-conical species combining a single large inner denticle on the lateral radular tooth and a penis with broad base and slender, parallelsided distal end. A single position of type 1 characterizes this new species (Table 3).

Sulawesidrobia carsonae sp. nov. is dedicated to the American zoologist and writer Rachel Carson (1907–1964) whose influential 1962 book Silent Spring had a lasting effect on the global environmental movement.

Holotype (Fig. 4C)

INDONESIA • Sulawesi, Lake Matano, S-shore, Inco boat house, below guest house, on rocks; 02°30.696′ S, 121°20.352′ E; Sep. 2003; Glaubrecht, von Rintelen and Zitzler leg.; MZB Gst. 12118.

Paratypes (Figs 4D, 5B–C)

INDONESIA • 11 specs; same collection data as for holotype; MZB Gst. 12119 • 10 specs; same collection data as for holotype; ZMB 107079.

SHELL (Figs 2B, 3C, 4A–B). Short-conical, sutures very shallow, about 1.5 times as high as wide, shell and priostracum light brown; protoconch initially with fine pits rearranging to irregular longitudinal striae and ca 0.75 whorls; entire shell with 3.75 to 4.125 whorls, teleoconch without structure apart from growth lines; umbilicus a narrow slit; aperture orthocline, only slightly higher than wide.

OPERCULUM. Very light yellow and thin, paucispiral, nucleus eccentric.

EXTERNAL FEATURES. Epidermis entirely black with the exception of mantle rim and areas over distal genital glands and stomach; tentacles with ciliated field (Fig. 5B).

MANTLE CAVITY (N = 4). 13–16 ctenidial filaments; osphradium elongate lying centrally under ctenidium along 75% of its length.

DIGESTIVE SYSTEM. The radula has the formula R 5 1 5/2-3 2-3, L 1-2 1 5-6, M1 18-24, M2 23-27, denticles of central tooth pointed and basally fused, two rhachidial basal cusps were only rarely observed, the same holds for a second small inner denticle on the lateral tooth, mostly there is only a single, very large one (Fig. 6D); stomach without caecum, black; intestine follows pallial genital glands, in females closer than in males.

FEMALE GENITALIA (N = 2; Fig. 7C–D). Ovary starts 1–1.25 whorls below apex, comprises 0.5–0.7 whorls and covers the posterior stomach chamber; renal oviduct first coiling 180° clockwise, then 270° counterclockwise; no receptaculum seminis; bursa copulatrix spherical, behind albumen gland, bursal duct entering anteriorly; albumen gland milky-white, capsule gland bipartite, opaque-white.

MALE GENITALIA (N = 2; Fig. 8C–D). Testis a lobate sac, starts 0.5–0.75 whorls below apex, comprises ca 1.25 whorls, anteriorly overlapping stomach; vesicula seminalis coils along anterior quarter of testis; proximal and distal vasa deferentia insert close to middle of kidney-shaped prostate; penis with broad base and slender, parallel-sided distal end.

There is only one other short-conical congener with a single large inner denticle on the lateral radular tooth, viz S. crutzeni sp. nov. The latter is 1.6 times larger and has a penis with very broad base and continuously tapering long distal end, though. In addition, it lacks a bursa copulatrix (see below). Sulawesidrobia carsonae sp. nov. was highly supported in the phylogenetic trees (Figs 9–10,Supp. file 1) although it had only a single diagnostic alignment position of type 1 (Table 3).