Siphonaria lentula ( Iredale, 1940 )

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 : 126-127

Siphonaria lentula ( Iredale, 1940)

( Figs 46J–L, Q , 47J–K )

Mestosiphon lentulus Iredale 1940: 439 , fig 14, 15 (type locality: Lord Howe Island [ Australia]).— Jenkins 1983: 29; White & Dayrat 2012: 64.

Siphonaria australis — Hubendick 1946: 49 (in part; not Siphonaria australis Quoy & Gaimard, 1833 ).

Siphonaria (Mestosiphon) laciniosa — Morrison 1972: 57 (not Siphonaria laciniosa ( Linnaeus, 1758)) .

Material examined

Type material. Lectotype of Mestosiphon lentulus Iredale, 1940 , present designation, from LHI ; coll. R. Bell, 1912–14 ( AM C.103712 , Fig. 46J ). Forty-one paralectotypes, same data as lectotype ( AM C.103713 ).

Other, non-type material. Australia, LHI: Off NE side; 31°30.43’S, 159°04.22’E ( AM C.356975 d); 31°32.5’S, 159°03.75’E ( AM C.103712 d; AM C.103713 41d); near runway 31°32.176’S, 159°04.258’E, LHI 2017Apr04 -102 ( AM C.482039 p); lagoon near wharf 31°31.5’S, 159°03.45’E ( AM C.356974 d); Signal Point, 31°31.5’S, 159°03.88’E ( AM C.356977 d); 31°31.501’S, 159°03.580’E, LHI 2017Apr04 -104 ( AM C.585957 3p); 31°31.501’S, 159°03.578’E, LHI 2017Apr04 -099 ( AM C.546717 5p; C.546718 14p, C.585955 p [SK053], C.585956 p [SK054], C.585958 p [SK234], C.595975 p [M040]); between Old Settlement Beach and Dawson Point, 31°31.18’S, 159°03.45’E ( AM C.356978 6p, C.608189 p [SK051]) .

Taxonomic remarks. The description contains no original type designation ( Iredale, 1940: 439). There are two registered type lots in AM reference collection, one labelled ‘holotype’ ( AM C.103712) and another with same data as the ‘holotype’ ( AM C.103713, 41 d, paralectotypes). We consider all these specimens as syntypes.The specimen AM C.103712 is herein designated as the lectotype of M. lentulus 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 ( Figs 46K–L ; Table S1). The lectotype is the specimen figured in Iredale (1940: 441, pl. 34, fig. 14–15) matching the shell dimensions given in the original description. Hubendick (1946: 49) incorrectly treated S. lentula as a synonym of ‘ S. australis’ without examining types or topotypes. However, S. australis is a distinct species ( Jenkins 1983: 1, fig. 3a). Morrison (1972: 56–58) treated ‘ M. lentulus’ as a synonym of S. laciniosa based on similarity in shell form and ‘common reproductive development’. This synonymy is not supported by examination of type specimens and comparative morpho-anatomy.

External morphology. Foot sole, foot wall, cephalic folds, mantle evenly dark grey/brown; foot edge; mantle narrow, mantle edge unlobed thickened paler band, bands dark pigmentation aligning with rib interstice furrows; genital pore inconspicuous, located on foot wall to right anterior of right cephalic fold; two small black epithelial eye spots centralised on two thick centrally touching dark grey cephalic folds; thin, pale grey, large pneumostomal lobe part of the mantle, between the right ADMs, closes the pneumostome and anus at the mantle edge.

Shell ( Figs 46J–L, Q ; Table S9). Small sized (max sl mean = 9.9 mm, SD = 1.0 mm, n = 13); ovate often elongate; height medium; flattened, apex offset central slightly to posterior; apical sides anteriorly concave posteriorly convex; protoconch direction homostrophic (n = 3; Fig. 46Q ), shell whorl dextral; growth striae prominent growth lines often distorted, undulating; rib count (mean = 22, SD = 2.5, n = 13), whitish primary ribs raised, bent and crooked, broaden to, extend beyond and scallop the often growth deformed shell lip; 2–3 interspersed darker secondary ribs, black to brown rib interstices; fairly distinctive primary rib pattern, abutting paired raised primary ribs on siphonal ridge, flare out shell lip; segment area immediately behind siphonal ribs clear of any ribbing, 4–5 primary ribs span posterior end, 4 primary ribs span anterior end. Interior shell margin brown, shell lip coloured cream/white rays and black/brown infilling under primary/secondary ribs and rib interstices respectively; spatula dark brown, siphonal groove dark brown or white, ADM scar indistinct, coloured same as shell margin, cephalic muscle car concave; Thickening of shell lip and spatula occurs across larger shell sizes, translucent, infills and reduces lip scalloping, spatula becomes whitened;

Reproductive system ( Fig. 47J; n = 2). 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 to side of RAM; AO large, elongated bulbous, bluntly pointed (embeds into MG), centrally bent, merges with top of indistinct GA; ED long narrow, slightly twisted; EG relatively large, folded, elongated and pointed; flagellum F1 absent; AO, GA and ED all muscular white tissue; BD and CD jointly connect into GA between ED, AO and GP; BD longer and much narrower than CD with a prominent loop close to BC, both ducts smooth curved and pass together ( BD above CD) through RAM connecting into folds of MG; BC small translucent test bulbous, embedded in soft white folds of AG / MG complex; HD short coiled, links AG to a small brownish finely granulated HG; dark SV embedded within AG, AG larger than HG.

Spermatophore ( Fig. 47K ). Test thin, translucent (length = 1.47 mm, n = 1, possibly longer as flagellum appears incomplete); head bulbous, tip bluntly rounded, containing a white gelatinous mass; very short taper region into the filamentous transparent flagellum; both sections smooth, featureless; head shorter and much thicker than flagellum (head length = 0.69 mm, ~46% of SPM length; flagellum length = 0.78 mm; head width = 120 μm; flagellum width = 24 μm, n = 1); single SPM coiled in one bursa ( AM C.356978).

Comparative remarks. Siphonaria lentula ( atra group, unit 73) is the sister group of an unidentified species from Molokai (‘ S. atra group, unit 36’ by Dayrat et al. 2014). Both sequences together form a well-differentiated subclade ( Figs 1 , 2 ). Siphonaria lentula differs from its sister lineage by COI distances of ≥ 16.6% (Table S3). Siphonaria lentula occurs in sympatry with two congeners on LHI: For comparison with S. exulum refer to comparative remarks under that species. Siphonaria pravitas sp. nov. has more raised ribbing and edge scalloping, a shorter ED and BD, with no distal loop, a larger BC, and a more threadlike SPM. The SPM of S. lentula is not typical of the atra group. It is very short, bulbous ( Fig. 47K ).

Distribution and habitat. Endemic to LHI ( Fig. 48 ). In this study, found in sheltered to exposed places on rocky shores, at upper to mid-littoral level.

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 46. Shells of S. stowae, S. opposita, S. madagascariensis and S. lentula. A–C, M–O. S. stowae. A–B. Tas, Dodges Ferry. A. AM C.585265 [M110]. B. AM C.584835 [M109]. C. Vic, San Remo, AM C.585616 [SK393]. M. WA, Gnarabup Beach, AM C.398365, protoconch. N. Vic, in situ. O. Vic, animal. D–F, R–T. S. opposita. D. Lectotype of Mallorisiphon oppositus AM C.103714. E. Qld, Yeppoon, TS, AM C.585135 [M424]. F. Qld, Gladstone, AM C.585866 [M213]. P. Qld, Scarborough, AM C.585819 [M458, SK181]. R. Qld, animal. S. Qld, in situ. T. Protoconch, AM C.585126 [SK136]. G–I. S. madagascariensis, Madagascar, Itampolo. G. AM C.584818 [M267]. H. AM C.584959 [M272]. I. AM C.584957 [M270]. J–L, Q. S. lentula. J. Lectotype of Mestosiphon lentulus AM C.103712. K. LHI, TS, AM C.608189 [SK051]. L, Q. Protoconch, LHI, TS, AM C.546718 [SK053]. Unlabelled scale bars = 10 mm.

FIGURE 47. Reproductive morphology of S. stowae, S. opposita, S. madagascariensis and S. lentula. A–B. S. stowae, Tas, Dodges Ferry. A. AM C.584914 [SK216]. B. AM C.585264 [SK007]. C–G. S. opposita. C–D. Qld, Scarborough, AM C.585819 [M458, SK181]. E. Qld, Yeppoon, TS. AM C.585135 [M424, SK237]. F–G. Qld, Scarborough, AM C.585863 [M431, SK135]. H–I. S. madagascariensis, Madagascar, Itampolo, AM C.584818 [M267]. J–K. S. lentula, LHI, TS, AM C.608189 [SK051]. Scale bars = 1 mm.

FIGURE 48. Known occurrence records of S. stowae, S. madagascariensis, S. lentula, S. opposita and S. monticulus