Siphonaria rodriguensis, 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 : 179-180

Siphonaria rodriguensis sp. nov.

( Figs 71I, Q–R, 72E–F)

Material examined. Type material. Holotype, from Rivière Banane 19°11.25’S, 63°22.866’E, N coast Rodrigues; coll. A. Meunier and O. Griffiths, RG01-1, 20 Aug 2018 ( AM C.585197 [SK330], Fig. 71I) . Paratype same data as holotype ( AM C.585196 p [M427, SK133, protoconch D1], Fig. 71Q) .

Other, non-type material. Rodrigues: Anse Quiter, SW coast, 19°46.183’S, 63°22.866’E, RG02-1 ( AM C.585888 p) .

External morphology. Foot wall, mantle, cephalic folds and pneumostome evenly cream, foot sole darker, paler to foot edge; mantle translucent, narrower than foot wall, edge weakly lobed, thickened with broad white edge band; uneven dark/black pigmentation along foot wall and mantle join, concentrated over centre of cephalic folds.

Shell ( Figs 71I, Q; Table S9). Small sized (max sl mean = 8.8 mm, SD = 1.3 mm, n = 2), ovate; height medium; centrally broad, thickness thin; exterior even, smooth; protoconch direction weakly homostrophic (n = 2, Fig. 71Q), shell whorl dextral; apex offset to posterior and left of centre, apex offset growth reflected in apical ridge, apical banding fades from tan/brown at shell edge to pale protoconch; anterior and lateral apical sides convex, posterior weakly concave; ribs radiate from apex to shell lip, straight unraised, primary and secondary ribs indistinct, rib count (mean = 39.5, SD = 2.5, n = 2), primary ribs irregularly spaced, whitish, ridges narrow, dual ribs form siphonal ridge, secondary ribs brown/tan; shell edge un-scalloped, even; growth striae indistinct. Interior spatula glossy, white, inner margin to shell edge dark chocolate brown with narrow white rays aligning under primary ribs, extending from shell lip to inner margin; ADM scar indistinct; CMS straight; siphonal groove very weakly indented. Thickening or whitening of inner shell lip not observed.

Reproductive system ( Fig. 72E; n = 4). Positioned within coelom under the respiratory cavity, epiphallic parts positioned between RAM and BM close to MG. ED joins at underside of small GA, AO joins underside of ED, short, blunt, narrower than ED, smaller than GA; ED thick, elongated, centrally twisted, broader at EG, narrower than AO; single broad curled stubby flagellum F1, appears as extension of ED at connection with EG; AO, GA and ED all muscular white tissue; EG broad, relatedly large, soft white tissue; BD and CD connect in parallel to GA at opposite sides of GA, BD without distal loop or MA; BD longer and slightly thinner than CD, both ducts smooth and pass together between RAM and inner foot wall connecting into thick layered folds of MG ( BD over CD); BC relatively large, spherical, embedded along with part of BD in AG / MG; SV embedded in AG under BC; HD short narrow, coiled, links large AG to a much smaller yellowish granulated HG, AG and MG folded, soft white tissue, with outer sides curved reflecting the close positioning to curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 72F). Broad head with short flagellum (length = 1.62 ± 0.1 mm, n = 4); test thin, whitish, smooth, featureless; head section broad cylindrical, bulbous, centrally bent, rounded tip; short tapering section merges head to filamentous flagellum; head longer, wider than translucent flagellum (head length = 1.04 ± 0.02 mm, ~ 70% of SPM length, head width = 99 ± 2 μm, flagellum width = 17 ± 0 μm, n = 4); 5 and 14 SPM tightly packed in BC ( AM C.585197, C.585196).

Comparative remarks. In our mitochondrial phylogeny, S. rodriguensis sp. nov. ( laciniosa group, unit 68) is the sister species of S. sipho (unit 24). Both species are closely related to S. viridis ( Figs 1, 3). Siphonaria rodriguensis sp. nov. differs from S. sipho by COI distances of ≥ 14.9% and from S. viridis by ≥ 13.9% (Table S6). We found S. rodriguensis sp. nov. in sympatry with S. fuliginata on Rodrigues, Indian Ocean. For comparative remarks see under S. fuliginata . The shell of S. basseinensis Melvill, 1893 described from Bombay ( Fig. 14M, not reviewed herein) is similar in having a smooth and even exterior, paired flush ribbing, but differs in having a prominent siphonal ridge.

Distribution and habitat. Recorded as endemic to Rodrigues Island, Indian Ocean ( Fig. 73). In this study, found on exposed marine rocky shores, at upper and mid littoral levels ( Fig. 71R).

Etymology. Named after the type location of Rodrigues Island, Indian Ocean.