Siphonaria subatra 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 : 118-119

Siphonaria subatra Pilsbry, 1904

( Figs 43J–L, S–T , 44H–I )

Siphonaria subatra Pilsbry 1904: 36 , pl. 6, figs 60, 60a, b (type locality: Chichijima, Ogasawara [ Japan]).—Hirase 1907: 40; Abe 1940: 59; Hirase 1941: 94, pl. 121, fig. 13; Hubendick 1945: 29; Kuroda & Habe 1952: 86; Oyama et al. 1954: 19; Kuroda 1960: 43; Baker 1964: 159; Habe & Igarashi 1967: 28; Morrison 1972: 57; Galindo 1977: 416; Fukuda 1994: 50, 808, pl. 42; Higo et al. 2001: 142, fig. G4978; Hylleberg & Kilburn 2003: 133; Poppe 2010: 444; White & Dayrat 2012: 68.

Siphonaria (Siphonaria) subatra — Hubendick 1946: 51, pl. 3, figs 32–35.

Siphonaria atra — Lischke 1871: 105; Boettger 1892: 168; Pilsbry 1895: 5; Abe 1940: 59; Hirase 1941: 94, pl. 121, fig. 17; Kuroda 1941: 137; Kuroda & Habe 1952: 86; Oyama et al. 1954: 14; Habe 1964: 145, pl. 44, fig.17; Hirano & Inaba 1980; Fukuda 1994: 50, 804 (not S. atra Quoy & Gaimard, 1833 ).

Siphonaria (Siphonaria) laciniosa forma subatra — Christiaens 1980a: 79.

Mestosiphon atra — Habe & Kohno 1980: 23 (not S. atra Quoy & Gaimard, 1833 )

Siphonaria (Mestasiphon) subatra — Kira 1962: 201, pl. 69, figs 10a, b; Habe & Kosuge 1966: 113, pl. 4, fig. 22; Okutani 1982: 32.

Siphonaria unit 38— Dayrat et al. 2014: 268, fig. 5 R.

Material examined. Type material. Lectotype of Siphonaria subatra Pilsbry, 1904 from Chichijima , Ogasawara [ Japan] ( ANSP 86132 a, Fig. 43J ). Two paralectotypes same data as lectotype ( ANSP 86132 ) .

Other, non-type material. Japan, Okinawa: Tancha Bay, 26°27.897’N, 127°49.131’E, JP01-5 ( AM C.584932 1p, C.584932 p [SK332]), Tancha Bay , rocky point 26°27.941’N, 127°49.194’E, JP01-6 ( AM C.585663 6p, C.584930 p [SK349], C.584931 p [M499, SK318], C.584933 p [M498, SK317]) .

Taxonomic remarks. The original description is evidently based on a series of specimens ( Pilsbry, 1904: 36, pl. 6, figs 61, 61a–b). Baker (1964: 159) subsequently designated the lectotype. Dimensions of the lectotype ( Fig. 43J ) match the original figure in Pilsbry (1904: 36) reasonably well. The lectotype has also been figured by Higo et al. (2001: 142, fig. G4978a). Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 43K, L , Table S1). Hubendick (1946: 50) listed a ‘transitional form’of ‘ S. subatra <> S. atra ’ without mentioning the locality. However, the figured specimen ( Hubendick 1946: 50, pl. 5, figs 5–6) is here identified as a specimen of S. subatra . Morrison (1972: 56–58) treated S. subatra as a synonym of S. laciniosa based on similarity in shell form and ‘common reproductive development’. Christiaens (1980b: 79) treated S. subatra as a variety of S. laciniosa based on specimens from Ping Chau, Hong Kong. These samples indeed correspond to shell characteristics considered herein as typical of S. subatra (i.e., siphon ridge formed by 3–4 ‘coalescing’ small ribs). Je (1989: 29) incorrectly listed S. subatra as a synonym of Anthosiphonaria sirius (= S. sirius ).

External morphology ( Fig. 43S ). Foot wall, cephalic folds and pneumostomal lobe all evenly pale grey in colour with white subepithelial pustules; paler grey to foot edge, foot sole darker; mantle thin, translucent, wider than foot wall, weakly lobed without a thickened edge, pale band on mantle edge align with underside of ribs; no black pigmentation; two black ‘Eye’ spots prominent centrally on thickened cephalic lobes; pneumostome fold prominent.

Shell ( Figs 43J–L ; Table S9). Medium sized (max sl mean = 19.8 mm, SD = 3.3 mm, n = 7), ovate; height low; apex offset sightly posterior and central, apical sides convex, shell thickness thick; protoconch direction undetermined, shell whorl dextral; growth striae indistinct in bands; exterior uneven, dark brown to pale tan, weak radial colour banding, protoconch area pale, central band darker and shell edge dark brown; rib count (mean = 51.4, SD = 8.0, n = 7), primary rib ridges pale, narrow, ribs slightly bent, increasingly raised and strongly protrude beyond shell lip (often> 1mm) to unevenly scallop and corrugate the edge; 3–5 finer secondary ribs between primary ribs, rib interstices darker; siphonal ridge formed by closely paired primary ribs protrudes greatest. Interior shell margin dark chocolate brown to blue/grey, uneven blue/grey rays on shell margin aligned under primary ribs, siphonal groove prominent, often same colour as shell margin; spatula mottled dark chocolate to tan brown; ADM scar distinct, CMS convex, darker than shell lip; thickening of shell lip common, overcoats brown markings on shell margin with blue/grey, infills and reduces lip scalloping.

Reproductive system ( Fig. 44H; 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 between BM and RAM; AO prominent, large, reasonably long, broad bluntly pointed, joins at top of smallish GA; ED elongated, narrow, twisted; EG medium with folds, single bent thickish flagellum F1 appears as an extension of ED at join with EG; AO, GA and ED all muscular white tissue; BD and CD elongated, with opposing connections join into GA close to ED and AO; BD longer and narrower than CD with a prominent distal coiling with an MA on bend attaching to inner foot wall, CD broadens to MG end, BD smooth, both ducts pass together through outer side of RAM ( BD above CD) and bent before connecting into folds of MG; BC small, prominent with internal purple gel, embedded in MG, translucent test, medium and bulbous; coiled HD with brown markings links AG at lower end of a block-like elongated yellowish finely granulated HG; MG and AG soft white folded tissue; SV embedded within AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 44I ). Body cylindrical, thread-like, test thin, translucent, smooth, featureless (length = 9.17 mm, head length = 7.85 mm, n = 1, 86% of SMP length, AL = 16 mm; head tip tapered bluntly rounded, section containing a white core, tapers to a thin short flagellum; two SPM tightly folded in brown gelatinous mass in BC of one specimen.

Radula. Dentition formula 34:1:34 ( Hubendick 1946: 51).

Comparative remarks. In our phylogeny ( Figs 1 , 2 ), S. subatra ( atra group, unit 38) is the sister species of S. tenebrae sp. nov. (unit 92) from CI. Both species combined from the sister lineage of S. vudaensis sp. nov. (unit 37) from Fiji. Siphonaria subatra differs from S. tenebrae by COI distances of ≥ 15.1% and from S. vudaensis by distances of ≥ 13.3% (Table S3). Siphonaria subatra has been found in sympatry with three congeners in Okinawa. Siphonaria rucuana has a smaller, taller, shell with stronger ribbing and weaker edge scalloping, a larger, bulbous, blunt AO, and a longer BC. Siphonaria camura sp. nov. has a smaller, taller, more fragile shell with a less scalloped edge, larger, bulbous BC, BD without a distal loop, and a barbed SPM. Siphonaria tanchaensis sp. nov. has a larger, taller, paler shell with greater edge scalloping, patterned exterior, and a smaller AO and BC. For comparison with S. sipho refer to comparative remarks under that species. Siphonaria subatra exhibits a similar shell morphology to other species in the atra group. However, the extended projection of the multi rib formed siphonal ridge beyond shell edge is a major difference. A shell figured as ‘ S. atra ’ from Japan in Hirase (1941: pl. 121, fig. 17) corresponds well with characteristics typical of S. subatra . It is well outside the known distribution of this species. Specimens depicted as ‘ S. subatra ’ in Hubendick (1946: pl. 3, figs 32–35) are of two different species; figs 32, 35 from ‘Japan’ are specimens of S. subatra and figs 33, 34 from Mindanao and Java Sea are likely specimens of S. alba . Figured specimens in Kira (1962: pl. 69, figs 10a, b) from Amami Islands as well as from Okinawa ( atra group, unit 38) in Dayrat et al. (2014: fig. 5R, UF351784) exhibit features typical of S. subatra .

Distribution and habitat. Recorded from Okinawa, Japan ( Fig. 45 ). In this study, found on exposed rocky shores at sheltered positions across the mid-littoral level (43T).

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