Siphonaria cacao, Jenkins, Bruce & Köhler, Frank, 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 : 168-169

Siphonaria cacao sp. nov.

( Figs 63M–O, 64F–G)

Material examined. Type material. Holotype, from Island of Tubuai, Austral Islands , 23°52’S, 147°41’E, IRD- MNHN Stn. X02 ( MNHN IM-2007-35319 p [SK506], Fig. 63M). Two paratypes, same data as holotype ( MNHN IM-2007-35317 p [SK564], Fig. 63N; IM-2007-35318 p [SK565], Fig. 63O).

Other, non-type material. Austral Islands : Tubuai, 23°52’S, 147°41’E, X02 ( MNHN IM-2007-35316 p) .

External morphology (preserved). Animal exterior evenly cream, foot sole grey, paler to foot edge; mantle translucent, irregular widely spaced pigmentation spots on foot wall, concentrated over posterior and centre of cephalic folds.

Shell ( Figs 63M–O; Table S9). Small (max sl mean = 15.5 mm, SD = 0.5 mm, n = 3), circular ovate; height low; apex offset weakly left and strongly to posterior, apical sides straight to weakly convex; shell edge uneven; protoconch direction undetermined, shell whorl dextral; growth striae indistinct, exterior grey to pale brown and usually eroded, radial colour banding indistinct; shell thickness medium; rib count (mean = 38, SD = 1.6, n = 3), ~ 12 distinct uneven primary ribs, white to pale, fairly straight, rib growth uneven, ridges rounded, broaden to scallop and protrude beyond shell edge; 2–3 interspersed pale white finer secondary ribs, rib interstices darker; paired primary ribs form siphonal ridge, more prominent and extend shell edge further than at other primary ribs. Interior shell dark chocolate brown, shell lip thickened; paler uneven rays extend from the shell lip over the shell margin, align under primary/secondary ribs; spatula dark chocolate brown, maybe mottled blueish; siphonal groove clear, similar colour to margin and spatula; ADM scar distinct, CMS convex.

Reproductive system ( Fig. 64F; n = 1). Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned to anterior tightly between RAM and over back of BM. Join of AO, ED and GA together at top of GA, AO larger than GA, elongated, bluntly pointed, centrally bent, thicker than ED; ED wide, centrally bent, shorter and narrower than AO; AO, GA and ED all muscular white tissue; EG folded, block-like, flagellum F1 small indistinct; BD and CD similar in thickness, connect side-by-side into GA, directly opposite to ED; both ducts smooth and pass together through outer side of RAM connecting into MG ( BD over CD), BC bulbous, embedded in MG / AG; hermaphroditic glands inaccessible.

Spermatophore ( Fig. 64G). Thread-like, test thin, translucent (incomplete); head section cylindrical (head length = 2.1 mm, n = 1), tip bulbous bluntly rounded, containing a white gelatinous core, smooth, featureless; 1 SPM tightly coiled embedded in white gelatinous mass in single BC.

Comparative remarks. Siphonaria cacao sp. nov. ( atra group) is the only species found in Tubuai in this study. We were unable to sequence COI or 16S from the available samples.

Distribution and habitat. Recorded exclusively from Austral Islands , French Polynesia, Pacific Ocean ( Fig. 67). In this study, found on sheltered rocky shores (harbour at Island of Tubuai), intertidal.

Etymology. For the dark, chocolate-brown interior of the shell in this species; noun in apposition.