Siphonaria acmaeoides 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 : 114-115

Siphonaria acmaeoides Pilsbry, 1894

( Figs 43A–D, M–N , 44A–C )

Siphonaria acmaeoides Pilsbry 1894b: 6 , pl. 6, figs 19–22 (type locality: Prov. Boshiu [Boso Peninsula], Japan).— Pilsbry 1895: 6, pl. 6, fig. 19–22; Hirase 1941: 94, pl. 121, fig. 15; Kuroda & Habe 1952: 86; Azuma 1960: 62; Baker 1964: 159; Galindo 1977: 416 (as ‘ acmeaodes ’); Christiaens 1980b: 466; Higo et al. 2001: 142, fig. G4976; White & Dayrat 2012: 60.

Siphonaria (Patellopsis) acmaeoides — Hubendick 1945: 70, fig. 19; 1946: 30, pl. 6, fig 12–15; Habe & Kikuchi 1960: 64; Kira 1962: 201, pl. 69, fig. 9a, b (misspelled as ‘ Patellops ’).

Siphonaria zebra — Kuroda & Habe 1952: 86 (not S. zebra Reeve, 1856 ).

Planesiphon acmaeoides — Kuroda et al. 1971: 484, pl. 64, fig. 8; Habe et al. 1986: 23.

Siphonaria (Mouretus) acmaeoides — Christiaens 1980a: 79.

Siphonaria (Mouretus) acmaeoides paulae Christiaens 1980a: 79 , pl. 4B, D (type locality: Ping [Peng] Chau, [ Hong Kong, China].— Christiaens 1980b: 466.

Siphonaria (Planesiphon) acmaeoides — Inaba 1983: 149; Je 1989: 29; Noseworthy et al. 2007: 90.

Patellopsis acmaeoides — Trew 1983: 3.

Siphonaria zelandica — Dayrat et al. 2014: 261, ‘unit 26’ (in part), fig. 5A (not S. zelandica Quoy & Gaimard, 1833 ).

Material examined. Type material. Lectotype of Siphonaria acmaeoides Pilsbry, 1894 from Prov. Boshiu [ Boso Peninsula ], Japan; coll. Frederick Stearns ( ANSP 70726 a, Fig. 43A ). Two paralectotypes same data as lectotype ( ANSP 70726 ).

Holotype of Siphonaria (Mouretus) acmaeoides paulae Christiaens, 1980 from Ping [Peng] Chau , [Hong Kong, China] ( NHMUK 1977171 , Fig. 43D ).

Other, non-type material. Japan, Honshu: Boso Peninsula, Po int S of Chitose Beach, 34°59.240’N, 139°58.304’E, JP02-2 ( AM C.585393 10+p, AM C.584936 p [M496, SK315], C.584937 p [M500, SK319], C.585289 p [SK356], C.585513 p [SK334 protoconch H4], C.585918 p [SK335]) .

Taxonomic remarks. The description of Pilsbry (1894b: 16) does not contain an original type designation. Subsequently, Pilsbry (1895: 2, pl. 6, fig. 19–22) republished the original description based on three specimens but giving the dimensions for only one specimen. Baker (1964: 159) designated the lectotype ( ANSP 70726a), which matches the original dimensions given by Pilsbry (1894b: 16). Figures in Pilsbry (1895: pl. 6, figs 19–22) correspond reasonably well with the type specimens; fig. 19 (ventral) lectotype, figs 20 (ventral), 21 (dorsal) and fig, 22 (ventral) paralectotypes. The type specimen figured in Higo et al. (2001: fig. G4976, “ANSP 70726”) differs from the specimens in Pilsbry (1894b: 16). The type specimens ( ANSP 70726) of S. acmaeoides ( Fig. 43A ) are of the plicata group.

Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 43B , Table S1). Comparative morpho-anatomy and mitochondrial phylogenetics herein confirm that S. acmaeoides and S. zelandica arecloselyrelated,yetdistinctspecies. Christiaens (1980a: 79) recorded S. acmaeoides from Hong Kong and described a new subspecies, S. acmaeoides paulae Christiaens (1980a: 79 , pl. 4, figs B, D). The holotype of S. a. paulae ( Fig. 43D ) matches specimens of S. acmaeoides from Japan ( Fig. 43B ). The emphasised characters of this subspecies, a finer, thinner, more elliptical, lighter coloured shell without a ‘marked’ central area, are within the range of intraspecific variation. Therefore, we synonymize this taxon with the nominate form. Christiaens (1980a) record extends the distribution of S. acmaeoides from Honshu, Japan to Hong Kong ( Fig. 35 ).

External morphology ( Fig. 43N ). Foot sole dark grey, paler to foot edge; foot wall, foot edge, mantle, cephalic folds and pneumostomal lobe all evenly pale grey/yellowish in colour; mantle thin, translucent, wider than foot wall, weakly lobed and unbanded edge; no black/dark pigmentation; pneumostome fold large, long between right ADMs and within mantle; vivid yellow or white subepithelial pustules on cephalic lobes and pneumostomal fold; two black ‘Eye’ spots prominent centrally on thickened cephalic lobes.

Shell ( Figs 43A–C, M ; Table S9). Medium sized (max sl mean = 14.5 mm, SD = 1.9 mm, n = 8), circular ovate; height low; apex offset slightly posterior and laterally central, apical sides even, weakly convex; exterior pale brown, with irregular darker/black flecks between primary ribs; rib count (mean = 57.4, SD = 10.3, n = 8), ~ 15 primary ribs, whitish, fairly straight, ridges rounded, broaden to shell edge; 3–4 finer secondary ribs between primary ribs, rib interstices dark grey; ribs align with shell edge; growth striae indistinct; siphonal ridge not prominent, formed by paired primary and secondary ribs, more protruding at shell edge; weak radial banding, darker to shell edge; protoconch direction central flat (n = 1; AM C.585513 [SK334]), shell whorl dextral. Interior shell lip finely corrugated; shell lip and margin white with dark flecks to dark chocolate brown rays aligning under primary rib interstices; spatula colour variable golden to dark chocolate brown; siphonal groove and ADM scar prominent, paler than margin and spatula; CMS convex to straight, indistinct; thickening and whitening of shell margin occurs.

Reproductive system ( Figs 44A–B; n = 4). Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned between BM and RAM; GA large, AO indistinct absent; ED very short, twisted, very broad; EG very large with folds, single long narrow looped flagellum F1 very short appears as an extension of ED at join with EG; GA and ED all muscular white tissue; BD and CD connect in parallel into GA close to ED joint, both ducts narrow, smooth, featureless, similar length pass together between outer RAM and inner foot wall ( BD above CD), slightly bent before connecting into folds of MG; BD without distal loop or MA; BC small, translucent test, bulbous, embedded in MG; coiled brownish HD links white AG to finely granulated HG; MG and AG small folded soft white tissue; SV embedded within AG under BC; AG slightly smaller than HG, sides reflect curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 44C ). Body bulbous, elongated (length = 1.03 mm, n = 1, AL = 11 mm), test thin; head tip bluntly rounded, section containing a white gelatinous core, tapers to a thin flagellum and tip; both sections smooth, featureless; head longer, thicker than flagellum (head length = 0.89 mm; 87% of SPM length; flagellum length = 0.14 mm; head width = 243 μm; flagellum width = 24 μm), 1 SPM in white gelatinous mass in BC of one topotypic specimen.

Radula. Dentition formula 26:1:26 ( Hubendick 1946: 31).

Comparative remarks. Siphonaria acmaeoides ( atra group, unit 91) is the closely related sister species of S. zelandica ( Figs 1 , 2 ). Both species differ by COI distances of ≥ 5.8% (Table S4). Both species have a disjunct distribution with one species found in the northern ( S. acmaeoides ) and one in the southern Pacific ( S. zelandica ), each. Throughout its range, S. acmaeoides has been found in sympatry with three congeners. For comparisons with S. sirius and S. japonica refer to comparative remarks under these species. Siphonaria camura sp. nov., sympatric in Honshu and Hong Kong, has a smaller, taller shell with more raised ribbing, a darker brown interior, larger BC, and a larger, thread-like and barbed SPM. Siphonaria acmaeoides exhibits a shell morphology similar to other species of the plicata group; however, these are anatomically and genetically distinct: S. zelandica (temperate Australia), S. plicata ( Tonga), S. nuttallii (Hawaii), S. tongatapuensis sp. nov. ( Tonga), S. namukaensis sp. nov. ( Fiji and NC) and S. poindimiensis sp. nov. ( NC), S. yagasaensis sp. nov. ( Fiji) and S. monticulus (NC, Lifou) . Siphonaria acmaeoides resembles S. zelandica in shell sculpture, external morphology, and SPM. Both species occupy similar habitats (upper littoral, shallow rock pools, rarely on rock faces). However, closer examination of the type and topotypic specimens revealed that S. acmaeoides differs in shell geometry, wider rib ridges, external colouration, and secondary ribbing, larger size of GA and ED, smaller HD, longer and narrower BD and CD. Hubendick (1946: 31) correctly pointed out that ‘ S. acmaeoides ’ and ‘ S. bifurcata ’ (= S. zelandica ) had ‘very similar shells’. Dayrat et al. (2015: 268) considered both taxa as possibly conspecific based on similarities in shell morphology.

Distribution and habitat. Recorded from the type locality, Bose Peninsula, and Aichi Prefecture, Honshu, Japan ( Fig. 45 ). In this study found to be common on exposed rocky shores in crevices and small rock pools, upper littoral level ( Fig. 43M ).

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 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