Bensonella hooki Páll-Gergely, 2023

Páll-Gergely, Barna & White, Tom S., 2023, Solving the mystery of the misunderstood Bensonella plicidens (Benson, 1849) (Gastropoda: Stylommatophora: Hypselostomatidae), Journal of Natural History 56 (45 - 48), pp. 2011-2029 : 2023-2025

Bensonella hooki Páll-Gergely sp. nov.

( Figures 6 , 9 (c,d))

Boysidia (Bensonella) plicidens – Pilsbry, 1917 (in Pilsbry 1916 –1918): 198 (partim), pl. 34, figs 1, 2, 4

Type material

Holotype. NHMUK 20191114.1 , 1 shell ( SW: 1.72 mm, SH: 2.01 mm, AW: 0.83 mm, AH: 0.86 mm), Cherrapunji, Godwin-Austen coll.

Paratypes. NHMUK 20191114.2 , 782 shells, same data as for holotype; NHMUK 20191111 /B, 3 shells from a mixed sample identified as B . plicidens ( NHMUK 20191111 / A), Cherra , India; NHMUK 1903.7.1.2882/C, 1 shell from a mixed sample with B . plicidens, Moussorie, NW Himalaya, Godwin-Austen coll.; NHMUK 1906.2.2.190C, 6 shells from a mixed sample identified as B. plicidens ( NHMUK 1906.2.2.190B), Cherra Poonje , Khasi Hills, W. T. Blanford coll .; NHMUK 20191107 , 16 shells, Khasi , R . Beddome coll., no. 5024; NHMUK 1888.12.4.592–8, seven shells, Cherra, W . Theobald coll .; NHMUK 1903.7 . 1.2062, three shells, Diyung valley; NHMUK 20191113 , 13 shells, Cherrapoonji , Assam, GodwinAusten coll .; NHMUK 20191110 , six shells, Teria Ghat, Assam, H .F . Blanford coll .; NHMUK 20191112 , five shells, Khasi Hills, A .S . Kennard coll .; NHMUK 20191109 , 13 shells, Himalaya , originally glued to two pieces of paper, some detached); NHMW-MO-69532 (2 shells), Khasi Hills, Ind ., coll . Oberwimmer , ex coll . Stoliczka ; NHMW-MO-113727 (2 shells), Khasi, coll . Stoliczka , 1880 .xv.473; NHMW-MO-113725 (1 shell), Cachar, coll . Stoliczka 1870 .

Additional material. NHMUK 20191114.3 , 9 juveniles, same data as for holotype .

Diagnosis. A Bensonella species with a triangular-ovoid, reddish brown shell and hooked apertural barriers.

Description. Shell triangular-ovoid, height somewhat variable; apex rather blunt, shell colour reddish brown; sculpture with occasionally strong, widely spaced growth lines; spiral striae absent; aperture subrectangular with clearly isolated sinulus due to angular lamella and parietal tubercle; peristome white, strongly widened, expanded, not reflected; aperture with numerous barriers; parietal wall with an angular lamella having two parts: its outer part reaches peristome, its inner part forms an outside-pointing hook; parietal lamella deeply situated, hooked; third lamella between parietal lamella and columellarparietal junction is ca. half as high as parietal lamella, and also forms a hook; palatal wall with three long main plicae (suprapalatal plica, upper palatal plica, lower palatal plica, however it is possible that the uppermost plica is the upper palatal plicae) with hooked central parts, their outer parts very slender, low, reaching peristome; columellar lamella similar to palatal plicae, hooked; between the lowest palatal plicae and the columellar plicae there are two or three short, hooked plicae; there are additional short, low, deeply situated plicae above the suprapalatal plica inside the sinulus; parietal tubercle blunt, knob-like, sits on edge of palatal lip, at the position where the palatal lip forms a little sinus; lower part of columellar lip widened, sometimes a low denticle-like swelling discernible; umbilicus very narrow, rounded.

Measurements (in mm). SW = 1.58–1.77, SH = 1.84–2.3, AW = 0.74–0.83, AH = 0.79–0.92 (NHMUK 20191114).

Differential diagnosis. This new species differs from B. plicidens in the following traits: Bensonella hooki has a shell that is larger and darker in colour, with more widely spaced and stronger growth lines; spiral striation absent; aperture with wider peristome, and the palatal tubercle on the peristome edge is less pointed, rather knob-like. The most important difference is in the apertural barriers, which are always hooked in the new species, but are never so in B. plicidens .

Bensonella lakainguta has a more triangular shell (with straight side lines) and a more pointed apex, the shell colour is yellowish corneous (reddish brown in B. hooki sp. nov.), its parietal callus is adnate to the penultimate whorl (diverges to a greater distance from the penultimate whorl in B. hooki sp. nov.), the peristome is overall thinner and the parietal tooth on the peristome edge is more pointed. The dentition is strikingly similar.

Etymology. This new species is named after Captain Hook, a fictional character from J.M. Barrie̾s Peter Pan, referring to the hook-like apertural barriers. It is a Latin singular, masculine noun in the genitive case.

Distribution. Shells of this species were collected in the southwest (Mussoorie) and the southeast (Assam) Himalaya.

Remarks. Although shells with hooked and normal barriers have sometimes been included in mixed lots from the Himalaya, there are also several lots with only one ̍ type ̾ of apertural barrier. This, and the additional differences between the two types (i.e. B. plicidens and B. hooki sp. nov.) indicates that contrary to the previous view ( Budha and Backeljau 2017), these types are not morphological varieties of the same species, but represent two distinct species.

Figures

Figure 6. Bensonella hooki sp. nov. NHMUK 20191114, specimen 1 (holotype). All photos: B. Páll- Gergely.

Figure 9. a, b: Bensonella plicidens (Benson, 1849), NHMUK 56.9.15.69A, specimen 1 (same as Figure 4); c,d: Bensonella hooki sp. nov., holotype, NHMUK 20191114 (same as Figure 6); e,f: Bensonella lakainguta Hwang, 2014, HNHM 105323 (same as Figure 7(d)); g, h: Bensonella lakainguta, NHMUK 201901108 (same as Figure 8). All images: B. Páll-Gergely.