Siphonaria sirius Pilsbry, 1894

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 : 115-118

Siphonaria sirius Pilsbry, 1894

( Figs 43E–F, O–P , 44D–E )

Siphonaria sirius Pilsbry 1894a: 9 (type locality: Sagami and Kashiurazaki, Boshiu, Japan).— Pilsbry 1895: 5, pl. 6, figs 23–28; Hirase 1907: 40; 1941: 94, pl. 121, fig. 16; Hubendick 1945: 29; Kuroda & Habe 1952: 86; Azuma 1960: 62; Kuroda 1960: 43; Baker 1964: 159; Shikama 1964: 6; Habe & Igarashi 1967: 28; Galindo 1977: 416 (as “ sinus ”); Christiaens 1980a: 79; Smith 1981: 9; Inaba 1983: 145; Trew 1983: 7; Je 1989: 29; Morton & Morton 1983: 298, pl. 1K; Higo et al. 2001: 142, fig. G4977; Hylleberg & Kilburn 2003: 133; Chim & Tan 2009: 270; White & Dayrat 2012: 67, Dayrat et al. 2014: 269, fig. 5H.

Siphonaria (Siphonaria) sirius — Hubendick 1946: 50, pl. 3, figs 24–27.

Siphonaria (Mestosiphon) sirius — Habe & Kikuchi 1960: 60; Kira 1962: 200–201, text-fig, pl. 69, figs 12a, b; Habe 1971: 15, pl. 4, fig. 12.

Anthosiphonaria sirius — Kuroda et al. 1971: 483, pl. 64, fig. 9; Christiaens 1980a: 79; Inaba 1983: 145; Habe et al. 1986: 23; Je 1989: 29; Fukuda et al. 1992: 76, pl. 23, fig. 361a, b.

Siphonaria laciniosa forma sirius — Christiaens 1980a: 79.

Siphonaria laciniosa — Springsteen & Leobrera 1986: 285, pl. 81, fig. 19 (not S. laciniosa (Linneaus, 1758)) .

Siphonaria (Anthosiphonaria) sirius — Noseworthy et al. 2007: 90.

Material examined. Type material. Lectotype of Siphonaria sirius Pilsbry, 1894a from Sagami and Kashiurazaki , Boshiu, Japan; coll. Fredrick Stearns ( ANSP 70720 a, Fig. 43E ). Six paralectotypes same data as lectotype ( ANSP 70720 ). Seven paralectotypes of Siphonaria sirius Pilsbry, 1904 from Sagami Bay ( AM C.117637 ) .

Other, non-type material. Japan, Honshu: Point S of Chitose Beach, Boso Peninsula 34°59.240’N, 139°58.304’E, JP02-2 ( AM C.585395 10p, C.584940 p [M501, SK320], C.584941p [M502, SK321], p [SK336]) . China, Hong Kong: Cape D’Aguilar 22°12.28’N, 114°15.38’E ( ZRC 2001-1768 21p, ZRC.MOL.24902 p [SK176]) . Philippines: Mactan , Cebu 10°18.840’N, 124°01.707’E PHS04-1 ( AM C.585339 p) . Singapore: Lazarus Island 01°18.643’N, 103°57.077’E SI04-2 ( AM C.585227 p [M339]); East Coast Park , seawall, 01°18.643’N, 103°57.077’E SI01-2 ( ZRC Moll. 9121, p) . Indonesia: Pulau Panjang , Riau Islands 1°10.21’N, 104°18.905’E ( ZRC EA-ZJ 09, 4p) .

Taxonomic remarks. The description of Pilsbry (1894b: 9) does not contain an original type designation. Pilsbry (1895: 2, pl. 6, fig. 23–28) republished the original description with six figures and dimensions for a single specimen. Baker (1964: 159; ANSP 70720a) subsequently designated the lectotype, which matches the dimensions given in Pilsbry (1894a: 9) and the figures in Pilsbry (1895: 2, pl. 6, figs 23–24; Fig. 43E herein).A type was also figured in Higo et al. (2001: 142, fig. G4976). Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 43F ) and geographic series of additional specimens (Table S1).

The description of ‘ S. atra ’ in Reeve (1856: pl. 3, species 14) appears to be based on specimens of S. sirius and not S. atra (refer to taxonomic remarks under S. atra ). Hubendick (1946: 50) listed ‘transitional’ forms between ‘ S. sirius <> S. subatra <> S. zanda ’, not explicitly linked to a specimen or locality. The figured specimen ( Hubendick 1946: pl. 5, fig. 3, 4) is identified as a specimen of S. sirius . Je (1989: 29) incorrectly listed S. subatra as a synonym of Anthosiphonaria sirius (i.e., S. sirius ). Christiaens (1980a: 79) considered S. sirius as one of three ‘forms’ of S. laciniosa in Hong Kong. He stated that the shell possesses ‘heavier ribbing than atra , with six or more solid white ribs’ and that the ‘siphon is formed by one rib’, which is consistent with features typical of S. sirius ( Figs 43E, F ).

External morphology ( Fig. 43O ). Foot wall, cephalic folds and pneumostomal lobe all evenly cream in colour, paler to foot edge, foot sole grey; mantle thin, translucent, wider than foot wall, weakly lobed with a thickened edge, white bands on mantle edge align with underside of ribs; irregular black blotches of pigmentation on foot wall and concentrated over cephalic lobes; two black ‘Eye’ spots prominent centrally on thickened cephalic lobes; pneumostome fold prominent with white subepithelial pustules.

Shell ( Figs 43E–F ; Table S9). Medium sized (max sl mean = 18.6 mm, SD = 8.97 mm, n = 9), elongate ovate; height medium; apex offset central sightly left, apical sides straight to weakly convex, protoconch direction homostrophic (n= 1), shell whorl dextral; growth striae prominent in bands, weak shades of radial banding may occur, shell thickness medium; rib count (mean = 41, SD = 3.9, n = 9), 9–10 primary ribs pale white, straight, broad, raised and protrude strongly (some> 1 mm) beyond shell lip to prominently scallop and corrugate the edge; 2–4 finer brown secondary ribs between primary ribs, interstices narrow, darker, single primary rib forms siphonal ridge. Interior shell margin dark brown to tan, white rays align on shell margin under primary/secondary ribs, siphonal groove distinct, same colour as shell edge, points to right anterior; spatula white, some specimens may be dark chocolate brown; ADM scar distinct, CMS straight, paler than shell lip; thickening of shell lip translucent, infills and reduces lip scalloping, spatula becomes whitened.

Reproductive system ( Fig. 44D; n = 1). Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned over back of BM and to side of RAM; AO prominent, broad bluntly pointed, joins to top of GA; ED relatively short, strongly twisted, very broad with MA on bend; EG small; single short broad looped flagellum F1 appears as an extension of ED at join with EG; AO, GA and ED all muscular white tissue; BD and CD with opposing connections (bulbous at CD) join into GA between ED, AO and GP; BD longer and narrower than CD with a prominent distal loop without an MA, and looped immediately before BC, both ducts smooth and pass together through RAM connecting into folds of MG ( BD above CD); BC embedded in MG, translucent test, large and bulbous; HD brownish long coiled links AG to a small elongated narrow brownish coarsely granulated HG; MG and AG small folded soft white tissue; SV embedded within AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 44E ). Body cylindrical, thread-like (length = 15.21 mm, n = 1), test thin, smooth, featureless, translucent; head tip tapered bluntly rounded, containing a white gelatinous core, tapers to a thin flagellum and tip; head shorter thicker than flagellum (head length = 7.17 mm; 47% of SPM length; flagellum length = 8.41 mm; head width = 142 μm; flagellum width = 31 μm). 4 SPM tightly coiled in brown gelatinous mass in BC of one specimen.

Radula. Dentition formula 40:1:40 ( Hubendick 1946: 51).

Comparative remarks. In our molecular tree ( Figs 1 , 2 ), S. sirius ( atra group, unit 31) is the sister species of an unidentified species from Tonga ( Dayrat et al. 2014, unit 30). Both differ from each other by COI distances of ≥ 12.5%. Siphonaria sirius differs from other species by COI distances of ≥ 22% (Table S9). Throughout its range, S. sirius has been found in sympatry with nine congeners. Two congeners are sympatric in Honshu: For comparison with S. japonica refer to comparative remarks under that species. Siphonaria acmaeoides has a paler, narrower ribbed shell with dual ribs forming the siphonal ridge, a weaker scalloped shell edge, a reduced AO, shorter wider ED and F1, smaller BC, longer unlooped BD, and a smaller, drop-shaped SPM. Three congeners are sympatric in Cebu, Philippines: For comparisons with S. bifurcata and S. sipho refer to comparative remarks under these species. Siphonaria caubianensis sp. nov. has a dual-ribbed siphonal ridge, a more posterior and left offset apex, stronger scalloped shell edge, a larger AO, a smaller BC, and no distal loop. Two congeners are sympatric in Singapore: For comparison with S. viridis refer to comparative remarks under that species. Siphonaria alba has a dual-ribbed siphonal ridge with a less flared end, a weaker scalloped shell edge, whiter interior colouration, a larger AO and a shorter F1. Siphonaria radians , sympatric on Riau Islands, S China Sea, has a weaker scalloped shell edge, a dual-ribbed siphonal ridge, a larger wider and more pointed AO, and a smaller BC. Siphonaria camura sp. nov., sympatric in Hong Kong, differs by having a smaller, taller shell with a dual-ribbed siphonal ridge, a shorter, wider ED, a larger, bulbous BC, and barbed SPM.

Specimens from Japan figured in Hubendick (1946: pl. 3, figs 24–27), Kira (1962: 201, pl. 69, fig. 12a, b), Habe (1971: pl. 4, fig. 12), Kuroda et al. (1971: pl. 64, fig. 9), Fukuda et al. (1992: pl. 23, fig. 361a, b), and Dayrat et al. (2014: fig. 5H) are morphologically consistent with S. sirius as delineated herein. By contrast, a specimen from Korea figured as ‘ S. sirius ’ in Yoo (1976: 89, pl. 19, fig. 5) is a misidentification. A figured specimen from Palawan identified as ‘ S. laciniosa ’ in Springsteen & Leobrera (1986: pl. 81, fig. 19) is S. sirius (single rib forming siphonal ridge); the associated ventral figure appears to be a different specimen (i.e., not matching the scalloped edge; with a multi-rib siphonal ridge; possibly a specimen of S. alba ); the stated synonymy of S. atrata ( sic atra ) with S. laciniosa is incorrect. The figured specimen of S. sirius in Dharma (1992: pl. 17, fig. 2) from Indonesia is a misidentification and likely a specimen of S. alba based on shell features and distribution.

Distribution and habitat. Known from Japan, China, Philippines, Vietnam, Singapore and Sumatra ( Fig. 45 ). In this study found in sheltered positions on moderately exposed and exposed rocky shores, mid to upper littoral level, often associated with Lithothamium ( Fig. 43P ).

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 43. Shells of S. acmaeoides, S. sirius, S. rucuana and S. subatra. A–D, M–N. S. acmaeoides. A. Lectotype ANSP 70726a. B–C. Honshu, Boso Peninsula, TS. B. AM C.584936 [M496, SK315]. C. AM C.585918 [SK335]. D. Holotype of S. acmaeoides paulae NHMUK 1977171. M. Japan, in situ. N. Japan, animal. E–F, O–P. S. sirius. E. Lectotype ANSP 70720a. F. Japan, Boso Peninsula, AM C.584941 [M502]. O. Japan, animal. P. Japan, in situ. G–I, Q–R. S. rucuana. G. Lectotype ANSP 86131a. H–I. Okinawa, Tancha Bay, TS. H.AM C.584915 [M493, SK312]. I.AM C.584918 [M492, SK311]. Q. Okinawa, in situ. R. Protoconch, AM C.584912 [SK409]. J–L, S–T. S. subatra. J. Lectotype ANSP 86132a. K. AM C.584933 [M498]. L. AM C.584931 [M499]. S. Animal. T. In situ. Unlabelled scale bars = 10 mm.

FIGURE 44. Reproductive morphology of S. acmaeoides, S. sirius, S. rucuana and S. subatra. A–C. Honshu, Boso Peninsula, TS. A. AM C.584936 [M496, SK315]. B–C. AM C.585918 [SK335]. D–E. S. sirius, Hong Kong, ZRC.MOL.24902 [SK176]. F–G. S. rucuana, Okinawa, Tancha Bay, TS. F. AM C.584918 [M492, SK311]. G. AM C.584917 [SK377]. H–I. S. subatra. H. AM C.584933 [M498, SK317]. I. AM C.584931 [M499, SK318]. Scale bars = 1 mm.

FIGURE 45. Known occurrence records of S. thersites, S. acmaeoides, S. sirius, S. subatra and S. rucuana