Siphonaria plana Quoy & Gaimard, 1833

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 : 72-73

Siphonaria plana Quoy & Gaimard, 1833

( Figs 29A–D, M , 30A–B )

Siphonaria plana Quoy & Gaimard 1833: 342 pl. 25, fig. 21, 22 (type locality: ‘lle de France, dans les environs du Port Louis’ [ Mauritius, in the vicinity of Port Louis]).— Lamarck 1836: 558; Anton 1838: 26; Lamarck 1839: 205; Catlow & Reeve 1845: 100; H. Adams & A. Adams 1855 (in 1853–1858): 271; 1863: 271; Gould 1852: 359, Hanley 1858b: 152; Deshayes 1863: 83; Paetel 1873: 117; 1875: 92; Martens 1880: 310; Paetel 1883: 178; 1889: 429; Hubendick 1946: 69); Michel 1974: 243; Galindo 1977: 416; Trew 1983: 6, 8; Subba Rao & Dey 2000: 190; White & Dayrat 2012: 67.

Siphonaria ferruginea Reeve 1856 : pl. 5, species 26 (without type locality).— Deshayes 1863: 82; Lienard 1877: 59; Martens 1880: 310; Paetel 1883: 178; 1889: 428; Dall 1890: 299; Hubendick 1945: 29; 1946: 53; Michel 1974: 243; Galindo 1977: 416; Trew 1983: 5; Drivas & Jay 1988: 132, pl. 51, fig. 17; White & Dayrat 2012: 63.

Siphonaria feruginea Hanley 1858b: 152 .— Paetel 1873: 117; 1889: 428 (invalid; incorrect subsequent spelling of ferruginea ).

Siphonaria atra — Dautzenberg 1923: 24; Drivas & Jay 1988: 132, pl. 51, fig. 19 (not S. atra Quoy & Gaimard, 1833 ).

Siphonaria (Siphonaria) ferruginea — Hubendick 1946: 53, pl. 4, figs 16–19.

Siphonaria ‘atra group, unit 35’— Dayrat et al. 2014: 262–263, fig. 5M–N; Ossenbrügger et al. 2023: 38, figs 3–4.

Material examined. Type material. Lectotype of Siphonaria plana Quoy & Gaimard, 1833 , present designation, from Île-de-France [ Mauritius] ( MNHN IM 2000-35955 , Fig. 29A ). Two paralectotypes, same data as lectotype ( MNHN IM 2000-5056 ).

Three syntypes of Siphonaria ferruginea Reeve, 1856 ( NHMUK 1981001 , Fig. 29B ) .

Other, non-type material. Mauritius: Souillac , 20°31.467’S, 57°31.582’E, MRU01-2 ( AM C.584968 p [M254]); Nth Albion, MRU02-1 ( AM C.585734 21p, AM C.584969 p [M251]; C.584970 p [M252]) .

Taxonomic remarks. The largest syntype of S. plana is herein designated as the lectotype for the stabilisation of the name (Art. 74.1 of the Code). Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 29C ) and geographic series of additional specimens (Table S1). We establish S. ferruginea ( Fig. 29B ) as a new synonym. Reeve (1856) treated S. plana as a synonym of S. lineolata Sowerby I, 1835 based on specimens from Chile and Central America; which were misidentified (see Hubendick 1946: 68). Later, Carpenter (1864a 545) incorrectly considered S. ferruginea as a variety of the New World species S. lecanium Philippi, 1846 , intermediate between S. maura and S. palmata . Hubendick (1946: pl.4, figs 16–19) depicted specimens from Mauritius that closely resemble the type of S. ferruginea ( Fig. 29B ). However, his interpretation of this species is confused. He stated that S. plana was a ‘nondefined or insufficiently defined’ species that may be identical with ‘ S. kurracheensis var. luzonica or zebra ’. He also assigned specimens from Queensland figured by Iredale (1940: pl. 34, figs 26–27) as ‘ L. optivus’ under S. ferruginea . However, we treat L. optivus as a junior synonym of S. viridis . Morrison (1963: 8) erroneously considered S. ferruginea as a synonym of the New World species S. alternata (Say, 1826) . Subsequently, Morrison (1972: 56–58) treated S. plana as a junior synonym of S. laciniosa based on similarity in the shell and a ‘common reproductive development’. This synonymy is not accepted herein based on examination of types and supplementary material.

External morphology. Foot sole, foot wall, mantle, cephalic folds and pneumostomal lobe evenly pale grey/cream, paler at edge foot/wall; blotches of black pigmentation on centre of cephalic folds, faintly on foot wall; mantle narrower than width of foot wall, non-translucent, covers exposed inner shell lip, edge thickened, lobed, vertical bands of black pigmentation aligned with shell rib interstices; genital pore indistinct, located on foot wall to right anterior of right cephalic fold; two small black epithelial eye spots centralised on two centrally touching cephalic folds; pneumostomal lobe long under the mantle between the right ADMs.

Shell ( Figs 29A–D ; Table S9). Small to medium sized (max sl mean = 16.8 mm, SD = 2.1 mm, n = 3), circular ovate; height low; apex offset left central and slightly to posterior, apical sides weakly convex, straight to concave at posterior; shell edge uneven; protoconch direction heterostrophic (n=3), shell whorl dextral; growth striae prominent, exterior brown, radial colour banding often present, edge dark, mid pale, protoconch area darker; shell thickness medium; rib count (mean = 39.3, SD = 1.7, n = 3), ~ 20 distinct primary ribs, white to pale, fairly straight, rib growth uneven, ridges rounded, broaden to scallop and protrude beyond shell edge (<1 mm); 2 interspersed pale white finer secondary ribs, rib interstices darker; paired primary ribs on siphonal ridge, more prominent and extend further than other primary ribs. Interior shell dark chocolate brown, maybe mottled whitish; white rays extend from the shell lip to over the shell margin fading to the spatula, align under primary/secondary ribs, spatula dark chocolate brown; siphonal groove distinct, similar colour to margin and spatula; ADM scar distinct, CMS concave, variable colouration of shell interior common (e.g., Fig. 29D ).

Reproductive system ( Fig. 30A; 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 to anterior over back of BM and between RAM; size of RS small to animal size; GP singular, positioned through foot wall behind right cephalic fold, GA very small; AO short, narrow, bluntly pointed, joins at top underside of GA in conjunction with ED; ED elongated, broad, joins to back side of GA alongside AO; single short broad blunt centrally bent flagellum (F1), same width as ED, appears as extension of ED, marked by connection of very small white folded EG; AO, GA and ED all muscular white tissue; BD and CD connect closely side-by-side into upper GA, CD connection bulbous, BD twisted with distal loop and MA over ED, both ducts narrow smooth featureless, pass together through RAM connecting into MG ( BD above CD), BD often looped immediately in front of BC and longer than increasingly broader CD; BC large, elongated, embedded in folds of AG / MG; SV embedded on left side of AG; HD short, thick uncoiled, links AG to smaller yellowish granular HG; MG and AG folded, soft white tissue; both curved reflecting the close positioning to curvature of inner foot wall on right posterior of coelom; outer edge of small MG lobed.

Spermatophore ( Fig. 30B ). Thread-like, test thin, translucent (length = 10.17 mm, n = 1, AL = 14 mm); head section cylindrical, bulbous, centrally bent, rounded tip; test thin, smooth, featureless, translucent, tapers into short flagellum; head slightly shorter, wider than translucent flagellum (head length = 4.31 mm, ~ 42% of total length, head width = 103 μm, flagellum width = 17 μm, n = 1); six tightly coiled SPMs found in a single BC of a topotypic specimen ( AM C.584970).

Comparative remarks. In our mitochondrial phylogeny ( Figs 1 , 2 ), Siphonaria plana ( atra group, unit 35) is the sister taxon of unit 34 (= S. opposita sp. nov.). Both species are separated by COI distances of ≥ 8.1% (Table S3). Siphonaria plana differs from S. denticulata by COI distances of ≥ 14.8% and from other species by distances of ≥ 20% (Table S3).

Throughout the range of S. plana we found six congeners to occur in partial sympatry. Three are sympatric in Mauritius: For comparison with S. viridis refer to comparative remarks under that species. Siphonaria griffithsorum sp. nov. has a smaller, taller shell with weaker edge scalloping, larger AO, longer BC and F1. Siphonaria gemina sp. nov. has a smaller shell with more raised ribbing and weaker edge scalloping, a smaller BC, shorter BD, and shorter SPM. Siphonaria incerta has a smaller, taller shell with less raised ribbing and weaker edge scalloping, a larger AO, smaller BC, and longer F1. Two species are sympatric in Mozambique: For comparison with S. capensis refer to comparative remarks under that species. Siphonaria carbo has a smaller, darker shell with finer ribbing and weaker edge scalloping, an indistinct AO, larger, elongate BC, BD without bursal or distal loops, and a smaller, bulbous SPM.

Figured specimens ‘ atra group, unit 35’ in Dayrat, Goulding & White (2014: 263, fig. 5M, Q) as well as Ossenbrügger et al. 2023 (figs 3–4) correspond well with S. plana and fall into the same genetic cluster, unit 35, as topotypic specimens examined herein.

Distribution and habitat. Indian Ocean: recorded from Mauritius, Réunion, the Seychelles ( Ossenbrügger et al. 2023), and eastern Africa (Pemba Bay, Zanzibar) ( Fig. 28 ). Dayrat et al. (2014: 255) listed a single sequenced but unfigured specimen from Rangong Kampuan, Thailand in ‘unit 35’. The occurrence of S. plana in Thailand requires confirmation. Common in sheltered positions on moderately exposed inner-lagoon rocky intertidal marine shores across upper littoral levels.

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 28. Known occurrence records of S. crenata, S. capensis, S. guamensis, S. zelandica, S. plana and S. plicata

FIGURE 29. Shells of S. plana, S. plicata and S. lateralis. A–D, M. S. plana. A. Lectotype MNHN-IM-2000-35955. B. Syntype of S. ferruginea NHMUK 1981001. C–D. Mauritius, Nth Albion, TS. C. AM C.584970 [M252]. D. AM C.584970 [M254]. M. In situ. E–G, N–O, Q–R. S. plicata. E. Lectotype MNHN-IM-2000-35956. F–G. Tonga, Ha’atafu Beach, TS of S. tongensis. F. AM C.585275 [M418]. G. AM C.585276 [M419]. N. Holotype of S. tongensis UUZM 1576. O. In situ. Q. Protoconch, AM C.585278 [SK225]. R. Animal, Halafuoleva Beach. H–L, P, S–T. S. lateralis. H. Lectotype of K. innominata GNS TM1203. I. Holotype of Kerguelenia macquariensis AWMM MA.70376. J–T. Macquarie Is, TS of K. innominata. J. AM C.584961 [M469, SK271]. K. AM C.584960 [M468, SK270]. L. AM C.91959 [SK202]. P. Animal. S. In situ. T. Protoconch, AM C.584962 [SK272]. Scale bars = 10 mm.

FIGURE 30. Reproductive morphology of S. plana, S. plicata, S. lateralis and S. radians. A–B. S. plana, Mauritius, AM C.584970 [M252]. C–D. TS of S. plicata, Tonga, Tongatapu. C. AM C.585276 [SK106, M419]. D. AM C.585275 [SK104, M418]. E–G. S. lateralis, Macquarie Island, TS of Kerguelenella innominata. E–F. AM C.91959 [SK202]. G. AM C.584960 [M468, SK270]. H–I. Indonesia, Riau Islands, Neotype of S. radians ZRC.MOL.24912 [M519, SK435]. Scale bars = 1 mm.