Siphonaria griffithsorum, B. W. Jenkins & Köhler, 2024

Jenkins, Bruce & Köhler, Frank, 2024, Hidden in plain sight: Systematic review of Indo-West Pacific Siphonariidae uncovers extensive cryptic diversity based on comparative morphology and mitochondrial phylogenetics (Mollusca, Gastropoda), Megataxa 13 (1), pp. 1-217 : 153-155

Siphonaria griffithsorum sp. nov.

( Figs 57C–E, M–N, T, 59E–F)

Siphonaria ‘ laciniosa group, unit 25’—Dayrat, et al. 2014: 261 (in part).

Material examined. Type material. Holotype, from Souillac 20°31.519’S, 57°31.633’E, Mauritius; coll. B.W. Jenkins, MRU01-1, 9 Aug 2018 ( AM C.584963 [M256], Fig. 57A). Six paratypes, same data as holotype ( AM C.585910 4p), Souillac 20°31.467’S, 57°31.582’E, Mauritius; coll. B.W. Jenkins, MRU01-2, 9 Aug 2018 ( AM C.584966 p [M257], Fig. 57B; AM C.585909 p [SK389], Figs 57C, T).

Other, non-type material. Mauritius: Isle de la Passe 20°24’S, 57°46.133’E ( WAM S72343 7p) .

External morphology ( Fig. 57M). Foot sole, foot wall, cephalic folds and pneumostomal lobe evenly cream, foot edge and mantle paler; mantle narrow, edge lobed, thickened, faint grey banding aligning with shell rib interstices; faint grey pigmentation over cephalic lobes.

Shell ( Figs 57C–E; Table S9). small sized (max sl mean = 9.3 mm, SD = 0.5 mm, n = 2), ovate, height medium; apex offset weakly posterior and to left; apical sides convex, posterior concave to straight; protoconch direction weakly heterostrophic to central (n = 1, Fig. 57T), area black colouration, shell whorl dextral; growth striae weak; shell thickness thin; colouration uneven with some radial banding; rib count (mean = 41.5, SD = 1.5, n = 2); slightly raised, pale white, fairly straight, faintly protrude beyond shell lip; predominantly primary ribs, finer secondary ribs interspersed, develop between primary ribs with shell growth, rib interstices darker; siphonal ridge formed by paired primary ribs, protrudes past shell edge, otherwise indistinct. Interior evenly dark brown to black from margin to spatula, paler on shell lip aligning under rib ends, siphonal groove clear; ADM scar indistinct, CMS weakly convex; No evidence of growth variations in shell thickness or shell margin colouration.

Reproductive system ( Fig. 59E; n = 1): Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts lay over BM and to side of RAM, F1 folded over back of BM. ED distinct entry to top of GA; AO large, elongated, bluntly pointed hook, centrally bent, attached to top of large, bulbous GA; ED thick, elongated, centrally bent, twisted; AO, GA and ED all muscular white tissue; EG large, folded, soft white tissue; single elongated, centrally looped, broad, blunt flagellum F1 appears as extension of ED at EG join; BD and CD connect into GA in opposing directions close to ED attachment, both ducts smooth, short, thick, slightly bent, pass together between RAM and inner foot wall ( BD over CD) connecting into MG, BD with coiled distal loop; BC white opaque test, relatively large, bulbous, embedded along with part of BD in soft white folds of MG, inner edge of MG lobed; HD narrow, coiled, links soft white folded AG to small yellowish granulated HG; AG larger than HG, both with outer sides curved reflecting the close positioning to curvature of inner foot wall at right posterior quarter of coelom; SV embedded in AG close to BC.

Spermatophore ( Fig. 59F). Thread-like (length = 8.98 mm, n =1), translucent, test thin; head section bluntly rounded, evenly cylindrical, containing a core white gelatinous mass, tapers along the transparent flagellum to a thin tip; keel as high as body width occurs along mid ¾ of head section; both sections smooth, featureless. Head section longer wider than flagellum (head length = 6.89 mm, ~ 77 % of SPM length, flagellum length = 2.08 mm, head width = 103 μm, flagellum width = 17 μm, n = 1). 3 SPM tightly coiled embedded in whitish gelatinous mass in BC ( AM C.584966).

Comparative remarks. Siphonaria griffithsorum sp. nov. ( plicata group, unit 64) is well-individualised genetic lineage within the pectinate group. It represents the sister lineage of the species pair S. delicata sp. nov. and S. christmasensis sp. nov. ( Figs 1, 3). It differs from other species by COI distances of ≥ 23.7% (Table S7). We found S. griffithsorum sp. nov. in sympatry with two congeners: For a comparison with S. plana and S. incerta refer to comparative remarks under these species. Siphonaria griffithsorum sp. nov. closely resembles S. lirata from Guam by having a heterostrophic protoconch.

Distribution and habitat. Recorded as endemic to Mauritius, Indian Ocean ( Fig. 60). In this study, found in sheltered positions on exposed rocky shores, upper and mid littoral levels ( Fig. 57N).

Etymology. For Mary-Ann and Owen Griffiths, Mauritius, in recognition of their hospitality and selfless assistance with collecting provided to the first author whilst visiting Mauritius.