Siphonaria bifurcata Reeve, 1856

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 : 93-94

Siphonaria bifurcata Reeve, 1856

( Figs 35A–F, O–P, S , 36A–C )

Siphonaria bifurcata Reeve, 1856 : pl. 5, species 21 [not species 22]. Type locality: ‘Port Jackson, Australia’ [in error for Philippines, see remarks].— Trew 1983: 3; Jenkins 1983: 5, 28; White & Dayrat 2012: 61.

Siphonaria bifasciata Galindo 1977: 416 (invalid; misspelling of S. bifurcata ).

Material examined. Type material. Lectotype of Siphonaria bifurcata Reeve, 1856 , present designation, from ‘ Philippine Islands’ ( NHMUK 1979169 /1, Fig. 35A ). Three paralectotypes, same data as lectotype ( NHMUK 1979169/2-4 , Figs 35B–D ).

Other, non-type material. Philippines: NW Polillo Is, E Quezon, Bolunga District, nr Panukalan , 14°59’N, 121°49’E ( WAM S74096 p [SK073], WAM S74098 p [SK410, protoconch H8], WAM S113801 p [SK411], WAM S74097 p [SK412]); Cebu, Mactan Point, 10°20.014’N, 124°02.723’E, PHS04-2 ( AM C.585118 p [M414, SK097]) .

Taxonomic remarks. The largest syntype ( Fig. 35A ) is herein designated as the lectotype of S. bifurcata for the stabilisation of the name (Art. 74.1 of the Code). This specimen corresponds well with the specimen erroneously figured by Reeve (1856, pl. 3, fig. 21) as ‘ S. zebra ’. Inspection of the types of S. zebra reveal that this is a nominal species from eastern Australia, which is here synonymized with S. zelandica . Correspondingly, the types of S. bifurcata are not of an Australian species but are conspecific with freshly collected specimens from the Philippines. Therefore, we conclude that the original descriptions of these two species have accidentally been mixed up: The text of the description for species 21 (labelled as ‘ S. zebra ’) applies to the shell depicted in figure 22 and is based on the type material originally labelled as ‘ S. bifurcata ’ from the Philippines. In turn, the description of species 22 (labelled as ‘ S. bifurcata ’) applies to figure 21, which corresponds well with the type material of S. zebra from eastern Australia (= S. zelandica ; Jenkins, 1983: 28; White & Dayrat, 2012: 61). Hence, the description of ‘ S. zebra ’ (including the type locality but excluding the figure) is herein attributed to S. bifurcata based on the types. Correspondingly, the description of ‘ S. bifurcata ’ (including type locality but excluding the figure) is herein attributed to S. zebra also based on the types.

The concept of S. bifurcata in Hubendick (1946: 46) is confused. He appears not to have examined the types and must have been misled by the above-mentioned mix-up of descriptions in Reeve (1856). Hubendick (1946) mentioned ‘specimens examined’ from Port Jackson [Sydney], which is outside the known distribution of S. bifurcata . The shells figured by Hubendick (1946: pl. 2, figs 9–13) and the description of Hubendick (1946: 14, fig. 13) are herein attributed to S. denticulata and S. zelandica , respectively. Our delineation of S. bifurcata is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Figs 35E, F ) and geographic series of additional specimens (Table S1).

External morphology ( Fig. 35O ). External parts evenly pale cream without black pigmentation apart from faint shading at centre of cephalic folds; mantle lobed, translucent; single small black epithelial eye spots centralised on two centrally touching cephalic folds; pneumostomal lobe under the mantle, unpigmented, between the right anterior and right posterior ADMs.

Shell ( Figs 35A–F, S ; Table S9). Medium sized (max sl mean = 15.8 mm, SD = 4.4 mm, n = 2), elongate ovate; height low to medium; apex offset posterior and left, apical sides convex, protoconch direction weakly heterostrophic (n = 1; Fig. 35S ) shell whorl dextral; growth striae indistinct, irregular growth may create rib irregularities and offsets; shell thick, externally white; rib count (mean = 43, SD = 5, n = 2), ~11 primary ribs white, fairly straight but may be bent, raised, rounded ridge, most prominent with paired ribs forming siphonal ridge and prominent protrusion at right quarter; primary ribs broaden to and protrude beyond shell lip to strongly unevenly scallop and corrugate the edge; finer secondary ribs fill gaps between primary ribs, rib interstices narrow. Interior outer shell margin white with pale brown markings aligning under rib interstices, interior pink in one specimen ( Fig. 35E ); siphonal groove distinct, appears notched/raised, same colour as shell edge, points to right anterior; spatula mottled brown underlying white; ADM scar distinct, CMS straight, golden/brown; thickening of shell lip apparent, infills and reduces lip scalloping, spatula becomes whitened.

Reproductive system ( Fig. 36A, C; n = 3). Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned over and looped/ folded in front of BM and to side of RAM; AO large, elongated, bluntly pointed (embeds into MG), centrally bent, often with MA, joins to top of indistinct GA; ED relatively short, broad, slightly twisted; EG small, folded; at join of ED and EG a single long, narrow, twisted flagellum F1 joins as an extension of ED; AO, GA and ED all muscular white tissue; BD and CD junctions into GA (bulbous at CD) opposing between ED, AO and GP; BD longer than CD with a prominent distal loop, top of loop attached via a long MA to inner foot wall in front of BM, both ducts smooth, similar thickness, pass together through RAM ( BD above CD), CD connects to midsized bulbous translucent test BC, CD connecting into folds of MG; HD brownish small coiled, links AG to elongated narrow brownish coarsely granulated HG; MG and AG similar sized, folded soft white tissue, dark SV embedded within AG / MG, AG and HG sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 36B ). Thread-like, test thin, translucent (length = 6.78 mm, n = 1, AL = 15 mm); head cylindrical, broad, tip bluntly rounded, tapers into long flagellum; flagellum attached to inside of BC; both sections smooth, featureless; head longer and thicker than flagellum (head length = 4.79 mm, ~ 71% of total length, head width = 103 μm, flagellum width = 17 μm, n = 1); SPM tightly coiled in light brown gelatinous mass in one BC ( WAM S74097 ).

Comparative remarks. Siphonaria bifurcata ( atra group, unit 45) forms a well-differentiated subclade within the mitochondrial tree and is the sister clade of a subclade containing S. umbra sp. nov. and S. radians ( Figs 1 , 2 ). Siphonaria bifurcata is well-differentiated from any other species by COI distances of ≥ 29% (Table S4). This species has been found in Cebu, Philippines in sympatry with four congeners. For comparison with S. sipho refer to comparative remarks under that species. Siphonaria alba has a lower shell with a more scalloped edge, a narrower AO, larger BC, smaller GA, and a shorter F1. Siphonaria sirius (unit 31), has a more central shell apex and scalloped edge, darker external and internal colour, and a paler spatula. Siphonaria caubianensis sp. nov. has a slightly taller shell with wider primary ribs, a more strongly scalloped edge, darker external and internal colour, paler spatula, a narrower AO, strongly twisted ED, and bursal loop. The RS of S. bifurcata resembles that of several other species, such as S. denticulata , S. javanica , S. poindimiensis sp. nov., S. viridis , and S. tanguissonensis sp. nov. According to the phylogenetic tree ( Fig. 1 ), none of these species is closely related to S. bifurcata . The shell of S. bifurcata resembles that of other species in the laciniosa and atra groups, such as S. sipho , S. alba , and S. atra in that it exhibits variations of a thickened white shell lip. Several authors have been misled by the mix-up of text labels and figures in Reeve’s (1856) description and confused this species with S. zebra . Consequently, S. bifurcata was repeatedly listed as a junior synonym of S. zelandica , which it is not. Figures of ‘ S. bifurcata ’ from ‘Port Jackson’ [Sydney] in Hubendick (1946: pl. 2, figs 9–13) are herein attributed to S. zelandica . The RS figure of ‘ Ductosiphonaria bifurcata ’ in McAlpine (1952: 42) is also of S. zelandica . The SPM of ‘ S. bifurcata ’ from ‘Port Jackson’ depicted in Hubendick (1946: fig. 19) and reproduced in Berry (1977: fig. 19) closely matches that of S. denticulate but not of S. zelandica .

Distribution and habitat. Philippines, recorded from Mactan (Cebu), Quezon, and Siquijor islands ( Fig. 37 ). In the present study found in sheltered places on moderately exposed rocky shores, lower littoral level.

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 2. Maximum Likelihood phylogram (partial, species not collapsed). Clades G–I (atra group) 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 (seeTables 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 spread over two pages.

FIGURE 35. Shells of S. bifurcata, S. fuliginata and S. lirata. A–F, O–P, S. S. bifurcata. A. Lectotype NHMUK 1979169/1. B–D. Paralectotypes NHMUK 1979169/2-4. E. Philippines, Cebu, TS, AM C.585118 [M414, SK097]. F. Philippines, Polillo Is, TS, WAM S74096 [SK073]. O. Animal & P. Cebu, in situ. S. Protoconch, WAM S74098 [SK410]. G–I, Q. S. fuliginata. G. Holotype NHMUK 1981002. H. Rodrigues, AM C.585194 [SK369]. I. Rodrigues, AM C.585874 [M430, SK134]. Q. Rodrigues, in situ. J–N, R, T–V. S. lirata. J. Lectotype NHMUK 1979028/1. K–M. Paralectotypes NHMUK 1979028/2-4. N, R. Guam, Apra. N. AM C.585832 [M448, SK242]. R. AM C.585192 [SK252]. T–U. Guam, in situ. V. Protoconch,AM C.585833 [M449]. Unlabelled scale bars = 10 mm.

FIGURE 36. Reproductive morphology of S. bifurcata, S. fuliginata and S. lirata. A–C. S. bifurcata. A. Philippines, Polillo Is, TS, WAM S74096 [SK073]. B. Polillo Is, TS, WAM S74097 [SK412]. C. Cebu, TS, AM C.585118 [M414, SK097]. D–E. S. fuliginata, Rodrigues. D. AM C.585874 [M430, SK134]. E. AM C.585194 [SK369]. F–H. S. lirata, Guam, Apra. F. AM C.585832 [M448, SK242]. G–H. AM C.585833 [M449, SK162]. Scale bars = 1 mm.

FIGURE 37. Known occurrence records of S. bifurcata, S. fuliginata, S. lirata, S. exulum, S. belcheri, S. nuttallii, S. incerta and S. tasmanica