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. SWP 17-77 ( 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.

Figures

FIGURE 1. Maximum Likelihood phylogram based on analyses of a concatenated sequence data set of 16S and COI. Branches are collapsed at the species level. Branch labels give unit numbers and accepted species names. Numbers on branches indicate branch support employing 10,000 ultrafast bootstraps.Available genus-group names are shown next to their type species. Scale bar indicating modelled sequence divergence.

FIGURE 3. Maximum Likelihood phylogram (partial, species not collapsed). Clades J–L (laciniosa and plicata groups) of the tree shown in Fig. 1. Branch labels give specimen identifiers for new sequences or Genbank accession numbers for imported sequences from other studies and geographic regions (see Tables S1–S2 for details). Identical haplotypes are merged into single tips. Numbers on branches indicate branch support by employing 10,000 ultrafast bootstraps. Clade names give unit numbers and accepted species names. Scale bar indicating modelled sequence divergence.

FIGURE 78. Known occurrences of S. tenebrae sp. nov., S. poindimiensis sp. nov., S. umbra sp. nov., S. undans sp. nov., S. vudaensis sp. nov., S. waikoloaensis sp. nov. and S. yagasaensis sp. nov.

FIGURE 79. Shells of S. vudaensis sp. nov., S. waikoloaensis sp. nov., S. amara and S. yagasaensis sp. nov. A–C, K–L, M. S. vudaensis sp. nov., Fiji, Viti Vevu. A. Holotype AM C.584785 [SK119]. B. Paratype AM C.608181 [M289]. C. Paratype AM C.584862 [M292]. K. In situ. L. Animal. M. Protoconch, AM C.584863 [SK122]. D–F, N–O. S. waikoloaensis sp. nov., Hawaii, Big Island. D. Holotype AM C.584907 [M295, SK214]. E. Paratype AM C.585327 [SK254]. F. Paratype AM C.584673 [SK391]. N. In situ. O. Protoconch, AM C.584906 [SK206]. G. Holotype of S. amara NHMUK 1981016. H–J. S. yagasaensis sp. nov. H. Holotype AM C.584827 [M437]. I. Paratype AM C.584860 [M435]. J. Paratype AM C.584828 [M436]. Scale bars = 10 mm.

FIGURE 80. Reproductive morphology of S. vudaensis sp. nov., S. waikoloaensis sp. nov., S. yagasaensis sp. nov., Williamia radiata and Williamia sp. ‘Walters Shoal’. A–B. Holotype of S. vudaensis sp. nov. AM C.584785 [SK119]. C–D. Holotype of S. waikoloaensis sp. nov. AM C.584907 [M295, SK214]. E–F. Holotype of S. yagasaensis sp. nov. AM C.584827 [M437 SK226]. G–H. Williamia radiata. G. NZ, Poor Knights Is, NMNZ M.100391/1 [M601, SK555], reproductive organs and animal anterior. H. Walters Shoal, MNHN IM 2013-67370 [M567, SK556], reproductive organs, animal anterior, detail of epiphalic parts. Unlabelled scale bars = 1 mm.