Siphonaria tagaqaensis, 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 : 182-183

Siphonaria tagaqaensis sp. nov.

( Figs 74A–C, M , 75A–B )

Material examined. Type material. Holotype, from nr Tagaqa 18°11.802’S, 177°38.640’E, S. coast of Viti Levu, Fiji; coll. B.W. Jenkins, FI02-1, 22 Aug 2018 ( AM C.584852 [M275, SK182], Fig. 74A ) . Paratypes: Same data as holotype ( AM C.586005 3p, C.584854 p [SK287], Fig. 74B, C.584855 p [SK297], Fig. 74C ) .

Other, non-type material. Fiji, Viti Levu: nr Tagaqa , SW coast, 18°11.802’S, 177°38.640’E, FI02-1 ( AM C.584851 p [SK298]) .

External morphology. Foot sole grey; foot wall, mantle, cephalic folds, pneumostome evenly cream, paler to foot edge; irregular small blotches of black pigmentation on foot wall and centre of cephalic lobes; mantle slightly narrower than foot wall, covers exposed inner shell lip, wider at anterior, mantle edge strongly lobed with bands of black pigmentation aligned with shell rib interstices; genital pore indistinct, located on foot wall to right anterior of right cephalic fold; small black epithelial eye spot centralised on each of centrally touching cephalic folds; pneumostomal lobe under mantle, unpigmented, between the right ADMs.

Shell ( Figs 74A–C ; Table S9). Small to medium sized (max sl mean = 14.8 mm, SD = 1.7 mm, n = 4), ovate; height medium to tall; exterior very uneven, growth disjointed /discontinuous; apex offset central sightly posterior (usually eroded), apical sides convex, straight to concave at posterior; protoconch direction heterostrophic (n = 1), below apex, shell whorl dextral; growth striae prominent in bands, shell thickness thick; rib count (mean = 46, SD = 11, n = 4), marked size difference between primary and secondary ribs; 12–15 primary ribs white, prominent, fairly straight, increasingly raised rounded ridge, width broadens to and protrudes weakly beyond shell lip to unevenly scallop and corrugate the edge; paired slightly separated primary ribs form strongly raised siphonal ridge; secondary ribs fill spaces between primary ribs, fairly even in width, rib interstices narrow, darker; some irregular radial coloured banding, dark around apex, paler/cream with dark flecks between primary ribs in lower areas. Interior shell edge and margin white under ribs, brown rays/bands align under rib interstices extend from lip to ADM, siphonal groove distinct, whitish; spatula dark chocolate brown under apex, paler to ADM scar, CMS straight; thickening of shell lip apparent, infills and reduces lip scalloping.

Reproductive system ( Fig.75A;n =1).Proportionally RS very large structure to animal size, positioned within coelom under the respiratory cavity, epiphallic parts positioned over back of BM, F1 draped over left side of BM; very small GA, AO broad, bent, rounded, bluntly pointed, rests against MG, joins top of GA; ED long, narrow, slightly bent, joins side of GA; EG medium with folds, overlaps join of ED flagellum (F1) join, F1 long, narrow, appears as an extension of ED; AO, GA and ED all muscular white tissue; BD and CD (bulbous at join) connect closely together in opposing directions into GA close to ED and AO entries; BD with distal loop and MA, BD longer and slightly narrower than CD, both ducts smooth, narrow, both pass together through outer side of RAM ( BD above CD), connecting into folds of MG; BC embedded in MG, size medium, bulbous test soft translucent, SV embedded within AG; HD lobed, links AG to small brownish granulated HG, MG and AG small folded soft white tissue, anterior edge of MG lobed, AG smaller than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 75B ). Body cylindrical, elongate (length = 7.05 mm, n = 1); test thin, translucent; head bulbous, tip bluntly rounded, wide, evenly cylindrical, containing a core white gelatinous mass, tapers along the transparent flagellum to a thin tip; both sections smooth, featureless. Head section longer, much wider than flagellum (head length = 4.77 mm, n = 1, ~ 68% of SPM length, head width = 1.33 mm, flagellum width = 13 μm). 2 SPM tightly coiled and embedded in brown gelatinous mass in BC of holotype.

Comparative remarks. Siphonaria tagaqaensis sp. nov. ( laciniosa group, unit 66) represents a well-differentiated lineage in the phylogenetic tree ( Figs 1 , 3 ). It differs from other species by COI distances of ≥ 27% (Table S6). Siphonaria yagasaensis is anatomically similar concerning the shape of AO, ED, F1 and SPM, but differs in having a lower, thicker, paler, whitish shell. We found S. tagaqaensis sp. nov. in sympatry with two congeners on Viti Levu: For comparison with S. namukaensis refer to comparative remarks under that species. Siphonaria vudaensis sp. nov. has a smaller, taller shell with stronger scalloped edge, flared siphonal ridge, darker interior, a narrower AO, and a larger BC, and BD without a bursal loop.

Distribution and habitat. Recorded as endemic to Viti Levu, Fiji ( Fig. 74M ). In this study, found in sheltered positions on moderately exposed rocky shores at mid-littoral level.

Etymology. For the type locality of Tagaqa, S coast of Viti Levu, 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 74. Shells of S. tagaqaensis sp. nov., S. tanchaensis sp. nov., S. tanguissonensis sp. nov. and S. tenebrae sp. nov. A–C, M. S. tagaqaensis sp. nov., Fiji, Viti Levu. A. Holotype AM C.584852 [M275]. B. Paratype AM C.584854 [SK287]. C. Paratype AM C.584855 [SK297]. M. In situ. D–F, O–P. S. tanchaensis sp. nov. D–E. Okinawa, Tancha Bay. D. Holotype AM C.585615 [M495, SK314]. E. Paratype AM C.584912 [SK386]. F. Okinawa, Onna, paratype AM C.584913 [M505, SK326]. O. Onna, animal. P. Tancha Bay, in situ. G–J, N, Q–R. S. tanguissonensis sp. nov., Guam, Tanguisson Beach. G. Holotype AM C.584877 [M417]. H. Paratype AM C.584875 [M342]. I. Paratype AM C.584878 [M438, SK163]. J. Paratype AM C.584881 [SK253]. N. In situ. Q. Protoconch, AM C.584882 [SK141]. R. Animal. K–L, S–T. S. tenebrae sp. nov., CI, Point Flying Fish Cove. K. Holotype AM C.584664 [M305, SK256]. L. Paratype WAM S74050 [SK120]. S. In situ. T. Animal. Unlabelled scale bars 10 mm.

FIGURE 75. Reproductive morphology of S. tagaqaensis sp. nov., S. tanchaensis sp. nov., S. tanguissonensis sp. nov. and S. tenebrae sp. nov. A–B. Holotype of S. tagaqaensis sp. nov. AM C.584852 [M275, SK182]. C–D. S. tanchaensis sp. nov., Okinawa. C. Paratype AM C.584913 [M505, SK326], Tancha Bay. D. Onna, AM C.595924 [SK538]. E–H. S. tanguissonensis sp. nov., Guam, Tanguisson Beach. E–F. Holotype AM C.584877 [M417, SK102]. G–H. Paratype AM C.584878 [M438]. I–J. S. tenebrae sp. nov., CI, Ethel Beach. I. Holotype AM C.584912 [M305, SK256]. J. Paratype WAM S74050 [SK413]. Unlabelled scale bars = 1 mm.