Siphonaria incerta Deshayes, 1863

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 : 107-109

Siphonaria incerta Deshayes, 1863

( Figs 41A–C , 42H–L, O, Q, T–U )

Siphonaria incerta Deshayes 1863: 81 , pl. 7, figs 16–17 (type locality: Réunion).— Lienard 1877: 59; Martens 1880: 310; Paetel 1889: 428; Dautzenberg 1932: 10; Morrison 1972: 56; Michel 1974: 243; Trew 1983: 5; White & Dayrat 2012: 64.

Siphonaria parcicostata Deshayes 1863: 81 , pl. 7, figs 18–19 (type locality: Réunion).— Lienard 1877: 59; Paetel 1889: 429; Dautzenberg 1932: 10; Hubendick 1945: 29; 1947a: 163; 1947b: 3; Michel 1974: 243; Trew 1983: 6; White & Dayrat 2012: 66.

Siphonaria (Siphonaria) parcicostata — Hubendick 1946: 46, pl. 3, figs 113–15.

Siphonaria sp. #335—Wells et al. 1990: 76, pl. 73.

Siphonaria sp. 2 — Wells & Slack-Smith 2000: 113; Tan & Low 2014: 367.

Material examined. Type material. Neotype of Siphonaria incerta Deshayes, 1863 , present designation, from Cap de la Houssaye , Saint Paul, Réunion (Art. 76.1 of the Code) ( NMHN IM-2000-35954 [M263], Fig. 42H ).

Other, non-type material. Réunion. TS ( AM C.585204 [M260], Fig. 42I ), Saint Denis , 20°53.108’S, 55°28.577’E, RU01-1 ( AM C.585906 p [M259, SK276]); Cap de la Houssaye Saint Paul, 21°01.086’S, 55°14.115’E, RU02-1 ( AM C.585204 p [M260], C.585205 p [M261], C.585206 p [M262], C.5859061 p [M261]) . Mauritius: Isle de la Passe , 20°24’S, 57°46.133’E ( WAM S72341 3p); Souillac, 20°31.467’S, 57°31.582’E, MRU01-2 ( AM C.585975 6p, C.584967 p [M258]); Souillac, 20°31.519’S, 57°31.633’E, MRU01-1 ( AM C.585974 17p, C.584964 p [M253], C.584965 p [M255]) . Australia, CI: E side Smith Point , Flying Fish Cove, 10°25.749’S, 105°39.957’E, CI01-2 ( AM C.584701 7p, C.584840 p [M320], C.584841 p [M321], C.584842 p [M322], C.585203 p [SK068]; WAM S74099 3p); West White Beach, 10°27.748’S, 105°34.934’E, CI01-3 ( AM C.5847021 4p, C.584843 [M309], C.584844 p [M310]; WAM S74100 3p); Ethel Beach, 10°27.827’S, 105°42.497’E, CI02-1 ( AM C.584847 p [M302], C.584848 p [M303], C.584889 p [SK081]; WAM S74101 5p) .

Taxonomic remarks. The type locality of S. incerta and S. parcicostata can be deduced from the title of article that contains the descriptions (= Réunion). The type specimens of both taxa are missing (V. Hero MNHN, pers comm.). Two original hand-drawn coloured figures of shells in Deshayes (1863: S. incerta (figs 16, 17) and S. parcicostata (figs 18, 19) provide the only indication of species identity. The neotype of S. incerta ( Fig. 42H ) is designated herein to clarify the taxonomic status of this taxon (Art. 75.3.1 of the Code). Shell differences between the original figures of S. incerta and S. parcicostata are insignificant and within the observed range of variation of S. incerta ( Fig. 42H, I–L, O ; see also Dautzenberg, 1932: 10). Therefore, S. parcicostata is herein treated as a junior synonym of S. incerta by First Reviewer’s Choice. Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly preserved specimens from Réunion, Mauritius, and Christmas Islands, including the neotype of S. incerta ( Fig. 42H , Table S1).

Hubendick (1946: 47) considered S. incerta Deshayes1863 as a possible synonym of S. laciniosa (Linne, 1758) without having examined from Réunion or other Mascarene Islands. Morrison (1972: 56–58) treated S. incerta as a synonym of S. laciniosa based on similarity in shell form and ‘common reproductive development’. This synonymy is not supported by our examinations.

External morphology ( Fig. 42T ). Foot sole, foot edge, foot wall, mantle, cephalic folds and pneumostomal lobe all evenly pale yellow to white in colour without any darker pigmentation markings. Mantle translucent, as wide as foot wall, strongly lobed with a thickened intense yellow to white banded edge; mantle lobes large, align with undulations of primary shell ribs, foot wall and pneumostome pustulose, pneumostome wide, between right anterior and posterior ADMs and within mantle; some individuals with dark brown shell rib interstices and interstice aligned dark pigmentation in mantle.

Shell ( Figs 42H–L, O, U ; Table S9). Small to medium sized (max sl mean = 13.5 mm, SD = 2.4 mm, n = 15), ovate, flattened, height medium to tall; apex offset posterior and centre, apical sides convex, posterior side straight to weakly concave; protoconch direction heterostrophic to central (n = 3; Fig. 42U ), shell whorl dextral; growth lines indistinct; rib count (mean = 30.7, SD = 6.9, n = 15), raised, whitish, weakly wavy, width increases strongly to shell lip; rib interstices black to dark brown; 12–14 prominent primary ribs, extend up to 1 mm beyond shell edge, rib extremities weakly up turned; 1–2 finer secondary ribs may occur between primary ribs; paired primary ribs over siphonal ridge; shell lip uneven, scalloped aligning with protruding ribs; interior colouration matches white primary ribs and dark brown rib interstices, from shell lip to over shell margin to the chocolate to golden coloured spatula; ADM scar impression distinct, same as shell margin colouring, cephalic scar convex; thickening of shell occurs, white layering thickens and covers colouration of shell margin, spatula coated white.

The neotype ( Fig 42H ). Shell (sl = 11.5, sw = 9.1, sh = 3.9 mm) circular ovate; thin, apex offset weakly to posterior and left, ~18 whitish primary ribs, with 0–3 in between secondary ribs, rib interstices dark, siphonal ridge formed by adjacent dual primary ribs. Interior evenly dark brown, white rays on shell lip under ribs; RS ( Fig. 41A ) and SPM ( Fig. 41B ). Neotype specimen grouped within unit 72 ( S. incerta ).

Reproductive system ( Figs 41A, C; 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 to anterior between BM and RAM. Join of AO and GA distinct, AO larger than GA, elongated, bluntly pointed, slightly folded, thicker than ED; ED relatively short and narrow, EG elongated, bluntly pointed with a single very long, bent, twisted, thin flagellum F1, flagellum often lays on top of the BM; AO, GA and ED all muscular white tissue; BD and CD jointly connected to GA between ED, AO and GP; BD slightly longer and thinner than CD with a prominent loop over GA, both ducts smooth and pass together through RAM connecting into MG ( BD over CD), BC small and bulbous, HD short thickened coiled, links AG to a small elongated narrow yellowish granulated HG; MG and AG small, folded, soft white tissue; SV embedded on left side of AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Fig. 41C ). Long thread-like; head section (head length = 6.06 mm, head width = 80 μm, n = 1) cylindrical, bulbous, rounded tip, tapers to flagellum; test thin, smooth, featureless, translucent encasing a white opaque central core; a short tapering section merges head to filamentous flagellum; head section wider than translucent flagellum (incomplete); 2 SPMs tightly coiled in brown gelatinous mass in bursa of the neotype.

Comparative remarks. Siphonaria incerta ( atra group, unit 72) is the sister species of S. recurva (plus an unidentified Siphonaria from Tuituila Island) in our phylogenetic tree ( Figs 1 , 2 ). Both species differ from each other by COI distances of ≥ 16.7%. From other species it differs by distances of ≥ 25% (Table S3). Throughout its range, we found seven congeners with partly sympatric occurrences. Five congeners are sympatric on CI: Siphonaria alba has a larger, lower, heavier shell with less raised ribs and a weaker scalloped shell edge, a smaller AO and BC, and a longer ED. Siphonaria christmasensis sp. nov. has a smaller, lower, darker shell with weaker ribbing and scalloped shell edge, dark spatula, and smaller AO and BC. Siphonaria delicata sp. nov. has a taller and brown/grey shell, with weaker ribbing and scalloped shell edge, and a larger BC. Siphonaria tenebrae sp. nov. has a lower shell with a less prominent siphonal ridge, stronger scalloped shell edge, and smaller AO and BC. Siphonaria umbra sp. nov. has a lower, paler shell with less raised ribbing, a weaker scalloped shell edge, darker spatula, a larger BC, and a shorter SPM. Two species are sympatric at Mauritius: For comparison with S. plana refer to comparative remarks under his species. Siphonaria griffithsorum sp. nov. has a smaller shell with less prominent siphonal ridge, even ribbing and weaker scalloped shell edge, and larger AO, ED and BC. Specimens from Mauritius and Port Natal figured as ‘ S. parcicostata’ in Hubendick (1946: 91, pl. 3, fig. 13–15) correspond well with features typical of S. incerta ( Figs 42H–L ). However, their identity remains uncertain.

Distribution and habitat. Known only from Réunion and CI ( Fig. 37 ); found in sheltered positions on moderately exposed and exposed rocky shores, mid littoral level ( Fig. 42Q ).

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 37. Known occurrence records of S. bifurcata, S. fuliginata, S. lirata, S. exulum, S. belcheri, S. nuttallii, S. incerta and S. tasmanica

FIGURE 41. Reproductive morphology of S. incerta, S. thersites and S. tasmanica. A–C. S. incerta. A–B. Réunion, Saint Paul, neotype MNHN IM-2000-35954 [M263, SK276]. C. CI, AM C.584889 [SK081]. D–G. S. thersites, Alaska, Cook Inlet. D–E. BIOUG 11BIOAK-0592 [SK553]. F. Dorsal view.G. Ventral view. BIOUG 11BIOAK-0589 [SK554]. H–I. Tas, TS of S. tasmanica. H. AM C.585255 [SK020]. I. SPM, AM C.585512 [SK080]. Unlabelled scale bars = 1 mm.

FIGURE 42. Shells of S. tasmanica and S. incerta. A–G, M–N, P–R, S. S. tasmanica, A. Neotype AM C.585259 [M114]. B–C, M–N. Syntypes of S. zonata, MV F.686. D–E. Largest syntypes of S. nereis AM C.108499. F. Largest syntype of S. turrita AM C.53828. G. Vic, Pt Lonsdale, AM C.585730 [M120]. P. Tas, Macquarie Harbour, in situ. R. Protoconch, AM C.585208 [SK019]. S. Tas, animal. H–L, O, Q, T–U. S. incerta, H. Neotype MNHN IM-2000-35954 [M263]. I. Réunion, Cap de la Houssaye, AM C.585204 [M260]. J. AM C.585205 [M261]. K. CI, Flying Fish Cove, AM C.584841 [M321]. L. CI, AM C.584843 [M309]. O. CI, TS, AM C.584840 [M320], Q. Réunion, in situ. T. Réunion, animal. U. Protoconch, AM C.585906 [M259]. Scale bars = 10 mm.