Siphonaria plicata 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 : 73-74

Siphonaria plicata Quoy & Gaimard, 1833

( Figs 29E–G, N–O, Q–R , 30C–D )

Siphonaria plicata Quoy & Gaimard 1833: 346 , pl. 25, figs 26– 27 (type locality ‘Île de Tonga-Tabou au village de Hifo’ [= Hihifo, Tongatapu, Tonga]).— Lamarck 1836: 557; Anton 1838: 26; Lamarck 1839: 205; Catlow & Reeve 1845: 100; H. Adams & A. Adams 1855 (in 1853–58): 271; Hanley 1858b: 152; H. Adams & A. Adams 1863: 271; Paetel 1873: 117; 1875: 92; 1883: 178; 1889: 429; Galindo 1977: 416; White & Dayrat 2012: 67.

Siphonaria tongensis Hubendick 1943: 6 , figs 4, 8 (type locality Foua, Tonga-Inseln [ Tonga]).— Hubendick 1946: 63, pl. 5, figs 29–31; White & Dayrat 2012: 68.

Siphonaria sipho — Reeve 1856: pl. 2, species 9; Hanley 1858b: 152 (not S. sipho Sowerby I, 1823 ).

Siphonaria (Siphonaria) laciniosa — Trew 1983: 6 (not S. laciniosa ( Linnaeus, 1758)) .

Material examined. Type material. Lectotype of Siphonaria plicata Quoy & Gaimard, 1833 , present designation, from ‘ Île de Tonga-Tabou au village de Hifo’ [ Hihifo , Tongatapu, Tonga] ( NMHN IM 2000-35956 , Fig. 29E ). Two paralectotypes, same data as lectotype ( NMHN IM 2000-5057 ) . Holotype of Siphonaria tongensis Hubendick, 1943 from ‘Foua, Tonga-Inseln’ [ Foua Island , Tonga]; coll. Eugenie Expedition, 1851–1853 ( UUZM 1576 , Fig. 29N ) . Paratype, same data as holotype ( UUZM 1576 ) .

Other, non-type material. Tonga: Tongatapu, Ha’atafu Beach Hihifo , 21°04.140’S, 175°20.048’W, TO02-1 ( AM C.585539 20+p, C.585275 p [M418, SK104], C.585276 p [M419, SK106], C.585277 p [SK105], C.585278 p [SK225]); Mau’i Rock, W coast Tongatapu, 21°08.154’S, 175°20.706’W, TO01-1 ( AM C.585431 20+p); Halafuoleva Beach, S coast Tongatapu, 21°08.358’S, 175°02.443’W, TO03-1 ( AM C.585947 20p, C.585283 p [SK223[); nr Kolonga, N coast Tongatapu, 21°12.021’S, 175°14.680’W TO04-2 ( AM C.585432 10+p, C.585432 p [SK380]) .

Taxonomic remarks. The largest syntype with best preserved external sculpture ( Fig. 29E ) is herein designated as the lectotype of S. plicata 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. 29F–G ) and geographic series of additional specimens (Table S1). We establish S. tongensis as a junior synonym based on the examination of the types ( Fig. 29N ). Reeve (1856) erroneously considered S. plicata as a synonym of S. sipho , a view adopted by Hanley (1858b: 152). Hubendick (1946) and Trew (1983: 6) placed S. plicata in the synonymy of S. laciniosa without providing an explanation or having examined the types. Morrison (1972) treated S. tongensis as a junior synonym of S. laciniosa based on similarity in shell form and for a ‘common reproductive development’.

External morphology ( Fig. 29R ). Foot sole centrally dark grey fading to yellowish at foot/wall edge; intensity of tissue colouration (i.e. of foot edge, foot wall and mantle) varies between paler and darker shell forms; external morphology is otherwise consistent; paler form ( LIF 01 and FI03-2)—foot wall and mantle intense yellow; darker form (TO03-1 and LIF02-1)—foot wall and mantle more greenish; both forms possess black pigmentation spots on foot wall, paler to foot edge; fringing mantle weakly lobed, translucent and reflects foot wall colouration, covers exposed inner shell lip; 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 cephalic folds; pneumostomal lobe thin, part of the mantle, between the right ADMs, closes the pneumostome at the mantle edge.

Shell ( Figs 29E–G, N, Q ; Table S9). Small to medium sized (max sl mean = 14.9 mm, SD = 0.4 mm, n = 6), ovate; height medium to tall; apex offset weakly posterior and to left, apical sides strongly convex, posterior side concave close to protoconch convex to margin; protoconch direction homostrophic to central (n = 3; Fig. 29Q ); shell whorl dextral; growth striae prominent in bands, shell thickness thick; ribs fairly even in width, rib count (mean = 56.3, SD = 1.7, n = 6), exterior uneven without prominent radial colour bands; primary ribs pale grey, fairly straight to wavy, slightly broaden increasingly raised to shell edge, ridges rounded narrow; edge finely scalloped and unevenly corrugated; 6–8 prominent spread radial ridges, one being siphonal ridge, each formed by 3–5 primary ribs; few finer secondary ribs, rib interstices darker grey; interior shell margin white, dark brown rays from shell lip over shell margin to spatula, align under rib interstices, siphonal groove distinct, same colour as shell margin; spatula golden brown to white; ADM scar distinct, darker brown, CMS convex; thickening and whitening of shell lip occurs ( Fig. 29E ).

Reproductive system ( Fig. 30C; 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 over back of BM, close to BC and to side of RAM; AO medium, broad, blunt, merges with MA, joins to inner side of a small GA; ED relatively short, centrally twisted, bent; EG folded, bulbous with pointed tip; single long narrow looped or bent flagellum F1 on EG; AO, GA and ED all muscular white tissue; BD and CD with opposing connections (bulbous at CD) into GA between ED, AO and GP; BD longer and narrower than CD with a prominent distal loop, top of loop attached via a long MA to inner foot wall in front of BM; both BD and CD smooth and pass together through RAM connecting into folds of MG ( BD above CD), BC small, translucent test and bulbous drop shaped; HD brownish, broad coils, links AG to a small elongated narrow brownish granulated HG; MG and AG small folded soft white tissue; dark SV embedded within AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 30D ). Test thin, translucent (length = 10.89 ± 1.66 mm, n = 2); head bulbous, tip bluntly rounded, containing a white gelatinous mass; taper region into the filamentous transparent flagellum is extended; both sections smooth, featureless; head longer and much thicker than flagellum (head length = 6.09 mm, head ~57% of SPM length; head width = 64 μm, SD = 1 μm; flagellum width = 1 μm); Six SPM tightly coiled in brown gelatinous mass in BC ( AM C.585275).

Comparative remarks. In our mitochondrial phylogeny, S. plicata ( plicata group, unit 56) is genetically well-differentiated. It is related to several species from Pacific Islands, such as Guam, New Caledonia and Hawaii ( Figs 1 , 3 ). The species differs from other species by COI distances of ≥ 25% (Table S7). In Tonga we found one sympatric congener, S. tongatapuensis sp. nov. which differs by having a more prominent dual ribbed siphonal ridge, a more central apex, lower height, paler interior colouration, a shorter wider ED, a larger pointed AO and longer BD. with bursal loop. Generally, the shell of S. plicata is similar to that of other species in the plicata group.

Distribution and habitat. Known only from Tonga ( Fig. 28 ). In this study found in sheltered positions (i.e., hollows on beach rock platforms, small pools, hollows of rocky cliff bases) on exposed rocky shores or landside of lagoons at mid and lower littoral levels. Two distinct forms appear to occupy different substrates: a smaller, taller shell morph ( ‘ monticulus ’-morph) occupies pits or hollows in vertical limestone cliffs, the larger, flatter shell morph was ( ‘ plicata ’-morph) is found on rock platforms, in hollows or on flat surfaces.

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 3. Maximum Likelihood phylogram (partial, species not collapsed). Clades J–L (laciniosa and plicata 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 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.