Siphonaria yagasaensis, 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 : 193-195

Siphonaria yagasaensis sp. nov.

( Figs 79H–J, 80E–F)

Material examined. Type material. Holotype, from Oneata Is , 18°26.5166’S, 178°29.583’E, Fiji. SWP 17- 116 ( AM C.584827 [M437, SK226], Fig. 79H) . Paratypes, same data as holotype ( AM C.584710 5p); Yagasa , small island to the SW, 18°57.783’S, 178°29.333’E, Tuvana-i-Ra Island, Fiji. SWP 17-103 ( AM C.584828 p [M436], Fig. 79J); Tuvana-i-Ra Island 21°02.24’S, 178°45.01’E, Fiji. SWP17-77 ( AM C.608181 p [M435], Fig. 79I) .

Other, non-type material. Fiji: Tuvana-i-Ra Island , SWP17-77, 21°02.24’S, 178°45.01’E ( AM C.585937 3p); Yagasa, small island, SW of Tuvana-i-Ra Island, SWP 17- 103, 18°57.783’S, 178°29.333’E ( AM C.585936 2p) .

External morphology (preserved). Foot sole and foot edge without dark pigmentation; foot wall, cephalic folds and pneumostomal lobe evenly cream with irregular blotches of black pigmentation, concentrated over centre of cephalic lobes; mantle translucent, wider than foot wall, edge weakly lobed, without pigmentation.

Shell ( Fig. 79H–J; Table S9). Medium sized (max sl mean = 16.7 mm, SD = 4.6 mm, n = 3), elongate ovate; low to medium; apex offset central slightly posterior and left, mostly externally coated with algae similar to Lithothamnion ; apical sides weakly concave, protoconch direction undetermined, shell whorl dextral, shell thick; rib count (mean = 33, SD = 4.9, n = 3), continuum of forms from primary to secondary ribs; primary ribs pale white, straight, slightly protrude beyond shell lip to unevenly scallop and corrugate the edge; 1–2 interspersed pale white finer secondary ribs, rib interstices narrow; paired primary ribs form siphonal ridge, no more prominent than other primary ribs. Interior shell lip/margin white of irregular widths and lengths, aligning under primary/ secondary ribs; spatula dark chocolate brown to ADM, siphonal groove deep and distinct, paler than shell margin and spatula; ADM scar distinct, CMS straight, same colour as spatula; thickening of shell lip common, often in smaller specimens ( Figs 79H, I), infills and reduces lip scalloping, becomes pale brown to dark cream.

Reproductive system ( Fig. 80E; n = 1). Positioned within coelom under the respiratory cavity, hermaphroditic complex ( HG, AG and MG) to posterior against right foot wall and over foot sole, epiphallic parts between BM and RAM, F1 lays over posterior of BM; AO large, elongated, centrally bent, blunt, merges to upper part of indistinct GA, singular GP; ED short, wide, twisted, short than AO, joins to lower side of GA and AO; GA, AO, ED all white muscular fibrous tissue; EG soft whitish, folded, smaller than AO; single short broad flagellum (F1), possible F2; BD and CD closely but in opposing directions connect to side of GA between AO and GP; both ducts smooth and pass through outside of RAM ( BD over broader CD); BD long narrow with prominent distal loop and MA attached to inner body wall in front of BM, joins to BC with thin transparent test; CD shorter wider than BD; CD connects into MG; BC and CD embed in folds of AG and MG; HD broad, lobed, brown markings, under AG, links AG to much smaller yellowish granulated HG; MG and AG folded, soft white tissue.

Spermatophore ( Fig. 80F). Thread-like (length = 3.04 mm, n =1), translucent, test thin; head section bluntly rounded, evenly cylindrical, containing a white gelatinous core, tapers along the transparent flagellum to a thin tip; both sections smooth, featureless; head section longer wider than flagellum (head length = 2.48 mm, flagellum length = 0.55 mm, head width = 56 μm, flagellum width = 11 μm, n = 1); SPM tightly coiled in bursa, embedded in brown gelatinous mass.

Comparative remarks. In our mitochondrial phylogeny ( Figs 1, 3), S. yagasaensis sp. nov. ( laciniosa group, unit 67) is the sister species of S. namukaensis sp. nov. (unit 22). Siphonaria yagasaensis sp. nov. differs from other species by COI distances of ≥ 13.9% (Table S6). For a comparison with S. namukaensis refer to comparative remarks under this species. Siphonaria yagasaensis sp. nov. exhibits a similar shell morphology with other species in the plicata group.

Distribution and habitat. Recorded exclusively to Oneata, small island SW of Yagasa and Tuvana-i-Ra Islands, southern Fiji ( Fig. 78). In this study, found on exposed and moderately exposed rocky shores, at upper littoral level.

Etymology. For the type locality, Yagasa Island, Fiji.