Siphonaria umbra, 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 : 188-191

Siphonaria umbra sp. nov.

( Figs 76D–E, L–M, 77C–D)

Material examined. Type material. Holotype, from Ethel Beach 10°27.827’S, 105°42.497’E Christmas Is, Indian Ocean; coll. B.W. Jenkins, CI02-1, 11 Sept 2018 ( AM C.584672 [M306], Fig. 76D) . Paratypes, same data as holotype, WAM S74051 p [M409, SK084], Fig. 76E).

Other, non-type material. Australia. Christmas Is: CI01-1 E side Smith Point Flying Fish Cove ( AM C.585320 p [SK022], C.585321 p [SK070]).

External morphology. Foot wall, foot edge and cephalic folds evenly yellow, foot sole darker yellow to grey; thick narrow; cephalic folds thin. large; mantle translucent, thin, mantle edge thickened lobed, white edge band; pneumostome long, under mantle.

Shell ( Figs 76D–E, L; Table S9). Small to medium sized (max sl mean = 12.14 mm SD = 0.16 mm, n = 3); height low to medium; elongate ovate; apex offset weakly posterior and left, often eroded; apical sides weakly convex anterior, weakly concave posterior, straight to concave lateral; protoconch direction weakly homostrophic (n = 2, Fig. 76L), shell whorl dextral; growth lines uneven wavy distorted; radial banding prominent; shell lip uneven, anterior slightly protruded; rib count (mean = 38, SD = 1.6, n = 3), primary and secondary ribs white, raised, extend slightly beyond corrugated shell lip, flare upwardly; often only one small or no secondary rib between primary ribs, rib interstices grey to brown; prominent primary rib gaps either side of and 3–4 times as wide as siphonal ridge, filled with 3–5 very small secondary ribs; siphonal ridge prominent raised rounded with 3 siphonal ribs; interior shell lip and margin dark brown with white rays of varying lengths aligning under primary ribs, extend to white to brown spatula; dark brown/black bands line either side of spatula, siphonal groove and ADM scar prominent; CMS straight to convex, similar but darker colouration to spatula and shell margin, shell margin noticeably wider at anterior; thickening of inner shell lip and spatula occurs in larger specimens, white layering coats and covers brown/ black colouration of inner shell lip.

Reproductive system ( Fig. 77C; n = 1). Relatively large to animal size; positioned against inside of foot muscle and foot wall on the right side within coelom, under the respiratory cavity. GA, EG and ED positioned between BM and RAM. AO large, elongated, bluntly bulbous, joins to small white muscular fibrous GA with singular GP; ED relatively short, straight, narrow, smaller than AO, joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG soft whitish, slightly folded, similar size to AO, with two flagellum, F1 long (similar length to ED), bent, appears as an extension of ED, internally lays on top of the BM; F2 short, straight, close to EG. BD and CD jointly connect to GA between ED, AO and GP; BD slightly longer and thinner than CD, with a prominent loop over and with MA to mid ED; both ducts smooth and pass closely together through RAM connecting into MG ( BD over CD), BC large, spherical, thin translucent test, (2 SPM in one BC), embedded in lower folds of MG / AG close to SV; HD short, narrow, coiled, links smallish AG to a large yellowish granulated HD; MG and AG small, folded, soft white tissue; AG larger than HG, sides match curvature of inner foot wall [M409].

Spermatophore ( Fig. 77D). Thread-like (length = 10.4 ± 2.1 mm, n = 6), test thin, translucent, comprises a translucent cylindrical body section containing a white gelatinous thread-like core, tapers rapidly into a filamentous transparent flagellum (head length = 10.3 ± 0.61 mm, ~78% of SPM length, head width = 140 ± 30 μm, flagellum width = 20 ± 0 μm, n = 2), head section thicker than flagellum, head tip bluntly rounded, both sections smooth, featureless; 4 SPM coiled, embedded in red-brown gelatinous mass [M409].

Comparative remarks. In our mitochondrial phylogeny ( Figs 1, 2), S. umbra sp. nov. ( atra group, unit 46) is the sister species of S. radians (unit 95). Both species are genetically well-differentiated differing by COI distances of ≥ 21.8% (Table S4). We found S. umbra sp. nov. in sympatry with five congeners on CI: For comparisons with S. alba , S. incerta , S. tenebrae sp. nov., S. christmasensis sp. nov., and S. delicata sp. nov. refer to comparative remarks under these species. Shell colour patterns resemble that of S. gemina sp. nov.

Distribution and habitat. Recorded as endemic to CI, Australia, Indian Ocean ( Fig. 78). In this study, found in sheltered positions on moderately exposed rocky shores, at mid to upper littoral levels ( Fig. 76M).

Etymology. From ‘umbra’ (Latin = shadow) for the two prominent axial dark areas both externally and internally at either side of the siphonal ridge and spatula groove in the shell of this species; noun in apposition.