Siphonaria rucuana Pilsbry, 1904

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 : 119-121

Siphonaria rucuana Pilsbry, 1904

( Figs 43G–I, Q–R , 44F–G )

Siphonaria rucuana Pilsbry 1904: 36 , pl. 6, figs 61, 61a, b (type locality: Riukiu Island [Ryukyu Islands, Japan]).—Hirase 1907: 40; 1941: 94, pl. 121, fig. 14; Hubendick 1946: 62; Kuroda & Habe 1952: 86; Oyama et al. 1954: 14; Habe 1962: 96, pl. 44, fig. 16; Baker 1964: 159; Christiaens 1980a: 81; Fukuda 1994: 50, 806; Higo et al. 2001: 142, fig. G4973; White & Dayrat 2012: 67.

Siphonaria zebra — Kuroda 1941: 137, pl. 3, figs 49–50 (not S. zebra Reeve, 1856 ).

Siphonaria laciniosa rucuana — Habe 1964: 144, pl. 44, fig. 16.

Siphonaria radians — Habe & Kosuge 1966: 113, pl. 42, fig. 24, 25 (not S. radians H. Adams & A. Adams, 1855 ).

Siphonaria (Siphonaria) rucuana — Higo 1973: 287; Noseworthy et al. 2007: 90.

Material examined. Type material. Lectotype of Siphonaria rucuana Pilsbry, 1904 from ‘ Riukiu Island’ [ Japan] ( ANSP 86131 a, Fig. 43G ). Three paralectotypes, same data as lectotype ( ANSP 86131 ).

Other, non-type material. Japan, Okinawa: Tancha Bay , 26°27.897’N, 127°49.131’E, JP01-5 ( AM C.585662 4p,C.584912 p [SK409, protoconch H9], C.584915 p [M493, SK312]; C.584916 p [SK355]; C.584917 p [SK377], C.584919 p [SK345], C.585082 p [SK406], C.585914 p [SK354], C.585915 p [SK383], rocky point, 26°27.941’N, 127°49.194’E, JP01-6 ( AM C.585627 6p, C.585917 p [M397], C.584918 p [M492, SK311]).

Taxonomic remarks. The original description of Pilsbry (1904: 36, pl. 6, figs 60a–b) is based on a series of specimens. Baker (1964: 159) subsequently designated the lectotype. The dimensions of the lectotype ( Fig. 43G ) match the original dimensions in Pilsbry (1904: 36) reasonably well. The lectotype has also been figured by Higo et al. (2001: 142, fig. G4973). Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 43H–I , Table S1). ‘ Siphonaria zebra (?)’ figured in Kuroda (1941: 137, pl. 3, figs 40, 50) is a specimen of S. rucuana . The ‘uncertain’ records of ‘ S. rucuana’ in Hubendick (1955: 7) are likely misidentified specimens of S. denticulata (from Etty Bay, Qld, MV F15040) and S. viridis (from Cape Edgecumbe [sic], Bowen, Qld, MV F15041). Habe (1962: 96, pl. 44, fig. 16) treated S. rucuana as an accepted species; however, Habe (1964: 144, pl. 44, fig. 16) treated it as a subspecies of S. laciniosa . This later treatment is not accepted.

External morphology. Foot sole pale brown, paler to foot edge; foot wall, mantle, cephalic folds and pneumostomal lobe all evenly dark yellowish; mantle thin, translucent, weakly lobed with a thickened dark yellowish banded edge; faint irregular black blotches of pigmentation on foot wall and cephalic lobes; pneumostome fold long between right ADMs and within mantle; genital pore inconspicuous, located on foot wall to right anterior of right cephalic fold; two small black epithelial eye spots centralised on two centrally touching unpigmented cephalic folds.

Shell ( Figs 43G–I, R ; Table S9). Small sized (max sl me = 9.2 mm SD = 0.7 mm, n = 10); ovate to elongate, height medium; apex offset central to weakly posterior; protoconch direction weakly heterostrophic (n = 2; Fig. 43R ), shell whorl dextral; apical sides convex, posterior weakly concave to straight; radial colour banding, protoconch area dark brown, centre pale grey, darker to uneven shell edge; growth lines distinct; rib count (mean = 28, SD = 3.1, n = 10) primary ribs whitish grey, straight, rib interstices dark brown/black; rib ridges rounded, broader to and weakly extend beyond shell lip, paired primary ribs form siphonal ridge, 0–1 finer grey secondary ribs between primary ribs, number greater either side of siphonal ridge. Interior shell lip weakly corrugated, with white rays aligning under primary ribs, and narrower dark brown/black markings under rib interstices; ADM scar prominent, CMS straight to weakly convex; shell margin and siphonal groove evenly dark chocolate brown, spatula white/grey; thickening or whitening of inner shell lip and spatula not observed.

Reproductive system ( Fig. 44F; n = 2). Positioned within coelom under the respiratory cavity, occupies the entire right side of coelom, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned over back of BM; GA prominent with singular GP through foot wall; AO medium, broad, blunt, joined to upper GA alongside ED; ED elongated, broad, slightly bent (no MA), joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG soft whitish tissue, slightly folded, joins ED; single broad flagellum (F1) with possible 2 nd shorter flagellum; appears as a continuous extension of ED to EG, laid over BM; BD and CD connect together in opposing directions into GA between ED / AO joint and GP, both ducts short, straight, smooth, thickened, whitish, featureless, pass closely together through outer side of RAM ( BD over CD) into soft white folded tissues of MG; MG / AG complex medium; BD narrower than CD, straight looped, end of loop attached to inner foot wall; BC medium, spherical, thin translucent test, embedded in outer folds of AG / MG; HD short, thickened, coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; outer edge of MG lobbed; AG larger than HG, outer sides of both matches curvature of inner foot wall.

Spermatophore ( Fig. 44G ). Thread-like (length = 6.88 mm, n =1), translucent, test thin; head section bluntly rounded, cylindrical, containing a core white gelatinous mass, tapers along the transparent flagellum to a thin tip; both sections smooth, featureless. Head section shorter wider than flagellum (head length = 2.74 mm, ~ 40% of SPM length; head width = 90 μm, flagellum width = 17 μm); 1 SPM in one BC ( AM C.584917).

Comparative remarks. Siphonaria rucuana ( normalis group, unit 83) differs from other species by COI distances of ≥ 24% (Table S6, Figs 1 , 4 ). The species has been found in sympatry with four congeners on Okinawa. Siphonaria camura sp. nov. has a smaller, taller, paler, fragile shell with a more offset apex and prominent ribbing, a smaller BC and AO, and a barbed SPM. Siphonaria tanchaensis sp. nov. has a larger, paler shell, with a patterned exterior and greater edge scalloping, and a smaller BC and AO. For comparison with S. sipho and S. subatra refer to comparative remarks under these species. Specimens figured as ‘ Siphonaria radians’ in Habe & Kosuge (1966: pl. 42, figs 24, 25) are attributed herein to S. rucuana . Siphonaria radians has less raised, finer ribbing, and a less prominent siphonal ridge.

Distribution and habitat. Known only from Okinawa, Japan ( Fig. 45 ). In this study, found on exposed rocky shores in sheltered positions (i.e., rock crevices and hollows; Fig. 43Q ), mid to upper littoral level (amongst green algae).

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 4. Maximum Likelihood phylogram (partial, species not collapsed). Clades C–F (normalis, lateralis and pectinata 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 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