Siphonaria exulum Hanley, 1858

(Figs 38F–T, 39E–H)

Siphonaria exulum Hanley 1858a: 25 (type locality: Norfolk Island).— Paetel 1889: 428; Coan & Kabat 2012: 336; White & Dayrat 2012: 63.

Siphonaria exulorum Hanley 1858b: 152 (invalid; unjustified emendation of S. exulum).— Paetel 1889: 428; Suter 1909b: 258; Oliver 1915: 547; Trew 1983: 5; White & Dayrat 2012: 63.

Siphonaria corrugata — Brazier 1888: 1001 (not S. corrugata Reeve, 1856).

Siphonaria lirata — Brazier 1888: 1001 (not S. lirata Reeve, 1856).

Ellsiphon (?) exulorum — Iredale 1940: 438.

Siphonaria diemenensis — Iredale 1910: 71 (not S. diemenensis Quoy & Gaimard, 1833).

Siphonaria atra — Iredale 1910: 71 (not S. atra Quoy & Gaimard, 1833).

Siphonaria raoulensis Oliver 1915: 545, pl. 12, fig. 40, 40a (type locality: Sunday Island [Raoul Island], Kermadec Islands, NZ).— Brook 1998: 232; Wood & Gardner 2007: 160; White & Dayrat 2012: 67; Duffy & Ahyong 2015: 67.

Siphonaria cheesemani Oliver 1915: 545, pl. 12, fig. 41, 41a (type locality: Sunday Island [Raoul Island], Kermadec Islands).— Jenkins 1983: 29; Brook 1998: 232; Wood & Gardner 2007: 161; White & Dayrat 2012: 61.

Siphonaria macauleyensis Oliver 1915: 545, pl. 12, fig. 42, 42a (type locality: Macauley Island, Kermadec Islands).— Brook 1998: 232; Wood & Gardner 2007: 161; White & Dayrat 2012: 65.

Siphonaria macauleyensis perplexa Oliver 1915: 545, pl. 12, fig. 43, 43a (type locality: Fleetwood Bluff, Sunday Island [Raoul Island], Kermadec Islands).— Brook 1998: 232; Wood & Gardner 2007: 161; White & Dayrat 2012: 61.

Siphonaria amphibia Oliver 1915: 545, pl. 12, fig. 44 (type locality: Sunday Island [Raoul Island], Kermadec Islands).— Brook 1998: 232; Wood & Gardner 2007: 161; White & Dayrat 2012: 61.

Parellsiphon innocuus Iredale 1940: 439, fig. 9, 10 (type locality: Norfolk Island).— Hubendick 1946: 49; Jenkins 1983: 29; White & Dayrat 2012: 64.

Siphonaria (Ductosiphonaria) diemenensis var. exulum — Hubendick 1946: 38–39.

Siphonaria (Ductosiphonaria) diemenensis var. perplexa — Hubendick 1946: 38–39.

Siphonaria normalis — Paul 1980: 14 (not S. normalis Gould, 1846).

Material examined. Type material. Holotype of Siphonaria exulum Hanley, 1858a from Norfolk Is [Australia] (NHMUK 1900.3.19.27, Fig. 38F).

Holotype of Siphonaria raoulensis Oliver, 1915 from Rocks between tide marks, Sunday Island, Kermadec Islands, [NZ] (CM M.3666, Fig. 38I). Four paratypes, Raoul Is; coll. W.R.B. Oliver (AM C.40293).

Holotype of Siphonaria cheesemani Oliver, 1915 from Sunday Island, Kermadec Islands, [NZ]; coll. W.R.B. Oliver (CM M.3660, Fig. 38J). Four paratypes, Raoul Is; coll. W.R.B. Oliver (AM C.40294).

Holotype of Siphonaria macauleyensis Oliver, 1915 from Macauley Island, Kermadec Islands, [NZ]; coll. W.R.B. Oliver 1908 (CM M.3663, Fig. 38K).

Holotype of Siphonaria macauleyensis perplexa Oliver, 1915 from Sunday Island, Kermadec Islands, [NZ]; coll. W.R.B. Oliver, 1908 (CM M.3661, Fig. 38L). Two paratypes, Raoul Is; coll. 1908, W.R.B. Oliver (AM C.40300).

Holotype of Siphonaria amphibia Oliver, 1915 from Fleetwood Bluff, Sunday Island, Kermadec Islands, [NZ]; coll. W.R.B. Oliver 1908 (CM M.3665, Fig. 38M). Two probable paratypes, Raoul Is; coll. W.R.B. Oliver (AM C.40299).

Syntype of Parellsiphon innocuus Iredale, 1940 from Norfolk Is; coll. 1910 (AM C.103708, Fig. 38N) .

Other, non-type material. NZ, Kermadec Islands: Raoul Island, Fishing Rock landing, 29°14.55’S, 177°54.22’W (AM C.608196 p [SK418 protoconch I5], C.595914 p [SK419 protoconch G12]); Boat Cove, 29°16.783’S, 177°53.65’W K2011-102 (AM C.475847 p [M513], 29°16.666’S, 177°53.717’W K2011-29-1 (AM C.475481 d); south side of Te Konui Pt, 29°18.53’S, 177°53.75’W. (AM C.475477 d, C.475479 d, C.475480 d) . South Meyer Island, 29°14.817’S, 177°52.817’W (AM C.475848 p [M512]) . Australia, NI: Anson Bay, NW side of NI, Stn D 3/2 rock pools, 29°00’S, 167°55’E (AM C.595968 p); Anson Bay, 29°00.550’S, 167°55.332’E NFI04-1 (AM C.585378 10p, C.585024 p [M219], C.585025 p [SK041]); Duncombe Bay, N side of NI, 29°00’02.5’S, 67°55’48.8’E (AM C.595965 10+p, C.595946 p [SK005]); Cascade Bay, 29°01.206’S, 167°58.174’E NFI05-1 (AM C.585551 26p, C.585026 p [M220],C.585027d[R001],C.585028d[R002],C.585029 p [SK010]); Ball Bay, 29°02’S, 167°59’E (AM C.595964 10+p); Ball Bay 29°02.844’S, 167°59.044’E NFI01- 1 (AM C.585526 20+p); Creswell Bay 29°03.478’S, 167°56.547’E NFI03-1 (AM C.585400 10+p, C.585023 p [M221]); Slaughter Bay 29°03.511’S, 167°57.416’E NFI02-1 (AM C.585581 30p, C.585020 p [M217], C.585021 p [M218],C.585022 p [SK009]); Emily Bay, S side NI 29°03’36.0’S 167°57’40.5’E (AM C.595967 p); Point Hunter Reserve, E side of cemetery 29°03’S, 167°58’E (AM C.595966 10+p, C.595944 p [SK042]); Point Hunter 29°03.629’S, 167°58.045’E NFI02-2 (AM C.585681 7p, C.595947 p [SK006]); Phillip Island 29°06.9’S, 167°56.88’E (AM C.585944 15p) . LHI: Signal Point 31°31.501’S, 159°03.578’E LHI 2017Apr04 - 099 (AM C.546717 5p, C.595945 p [SK052]); On marine debris Old Settlement, LHI, 31°31.18’S, 159°03.45’E (AM C.582859 8p, C.585945 p [M467, SK234]) .

Taxonomic remarks. The original description of S. exulum gives measurements for a single specimen, the holotype. The holotype is the only type specimen known to exist (J. Ablett, pers. comm. NHM). No type has originally been designated in the description of P. innocuus . The type specimen in Iredale (1940: 441, pl. 34, figs 9–10) is therefore considered as a syntype (Fig. 38N). No other type specimens are known. Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes of S. exulum (Figs 38G), P. innocuus (Fig. 38Q), S. raoulensis (Fig. 38O), S. cheesemani (Fig. 38P), S. macauleyensis and S. macauleyensis perplexa (Fig. 38O) and geographic series of additional specimens (Table S1). These analyses confirm the synonymy of P. innocuous, S. raoulensis, S. amphibia, S. cheesemani, S. macauleyensis and S. macauleyensis perplexa . Siphonaria amphibia, S. cheesemani, S. macauleyensis and S. macauleyensis perplexa had previously been synonymised with S. raoulensis by Wood & Gardiner (2007) based on molecular phylogenetic evidence. However, the relevant sequences are not available on Genbank (accessed 28 April 2021) precluding their use in this review.

Records of ‘ S. corrugata ’ and ‘ S. lirata ’ from Norfolk Island in Brazier (1888, 1001) are misidentifications attributed herein to S. exulum . Paetel (1889: 428) listed both S. exulum and its emendation S. exulorum as accepted species. Suter (1907: 265) misidentified specimens of this species from the Kermadec Islands as S. diemenensis . Oliver (1915: 545) described several species from the Kermadec, which he considered to be distinct although ‘difficult to separate’. All these species are synonyms of S. exulum . Iredale (1940, 438) apparently not being aware of Hanley’s description, incorrectly attributed the name exulorum to Suter and tentatively placed it in Ellsiphon . Hubendick (1946: 36, 38, 63) incorrectly treated S. cheesemani as a synonym of ‘ S. cookiana ’ (= S. propria); S. raoulensis, S. macauleyensis and S. perplexa as synonyms or varieties of S. diemenensis; and S. amphibia as a synonym of S. acmaeoides . However, he listed no specimens from the Kermadecs under ‘specimens examined’. Furthermore, Hubendick (1946: 38) also listed S. exulum and S. exulorum (‘Error for exulum ’) as varieties of S. diemenensis Quoy & Gaimard, 1833, which is not accepted herein. Morrison (1972: 56–58) treated ‘ Parellsiphon innocuous ’ ( sic innocuus) 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 morpho-anatomy. Trew (1983: 5) treated S. exulorum ( = exulum) as a synonym of ‘ Pachysiphonaria diemenensis ’. Grove (2006: 60) also synonymized S. exulum with S. diemenensis, but the specimen figured by Grove (2017) as ‘ S. exulum is actually an individual of S. diemenensis . Brook (1998: 232) stated that ‘there is only one morphologically variable species of Siphonaria, namely S. raoulensis, at the northern Kermadec Islands’. The correct name for this species is S. exulum, however.

External morphology (Fig. 38S). Foot sole smooth, evenly dark yellow to centrally greyish; foot wall narrow dark yellow with evenly spread white subepithelial pustules becoming more vivid and dense close to the foot sole and around pneumostomal lobe; fringing mantle narrow, yellowish translucent, extends to shell edge, outer edge lobed, strongly banded yellow, reflects the profile shell lip and ribs; pneumostomal lobe paler and within mantle between the right anterior and right posterior ADMs, closes the pneumostomal and anal openings at the mantle edge; two small black epithelial eye spots centralised on two thick centrally touching dark yellow cephalic folds that darken to their outer edge, covered with white mucous cells similar (but smaller) to those of the foot wall tissue; genital pore inconspicuous, located on foot wall to right anterior of right cephalic fold.

Shell (Figs 38K–M, R–T; Table S9). Small to medium sized (max sl mean = 14.4 mm, SD = 2.2 mm, n = 24); ovate, thin, height tall to flattened ( ‘ exulum ’, ‘ raoulensis’ and ‘ macauleyensis ’ forms, Figs 38H, K–O) to flat ( ‘ cheesemani ’ form, Fig. 38P); dark and pale shell forms variable, exterior uneven; apex fairly central and weakly offset to posterior; apical sides evenly convex; apex weakly hooked, protoconch direction homostrophic (n = 4; Fig. 38R), shell whorl dextral; rib count (mean 39, SD = 7, n = 24) slightly raised to strongly raised, primary ribs grey to white, fairly straight, very prominent in some individuals; few secondary ribs, develop between primary ribs to a similar size at shell margin, rib interstices dark brown to black; paired touching primary ribs over indistinct siphonal ridge; growth striae distinct, 2–3 discontinuous bands of brown radial shading, protoconch area dark brown; shell edge uneven, scalloped by weakly extending ribs; interior mottled brown to evenly dark brown, apart from short cream markings on shell lip aligning with primary ribs; spatula pale brown to blue/white, pale shell form has golden brown spatula. Siphonal groove shallow, ADM scar variably distinct, CMS convex. Translucent thickening of internal shell occurs, infills and reduces scalloping of lip, spatula becomes whitened (prominent in pale shell forms; ‘ innocuus ’; Fig. 38Q, P).

Reproductive system (Figs 39E, G, H; n = 3). Single GP located in foot wall on right posterior side of right cephalic fold; opens internally into a relatively small GA positioned between right dorsal of BM and RAM; elongated horn-shaped AO present protrudes as an extension of GA, a short wide whitish muscular tissued ED joins side of GA; a singular short thin blunt hooked cream-coloured flagellum F1 protrudes from the join between the ED and lobed blunt whitish EG; the long, narrow thickened whitish CD and thin smooth unlooped BD (BD thinner and dorsal to CD) together pass through the RAM to enter the GA close to GP (BD closest), posterior to entry of AO and ED; at the end of BD is a relatively small spherical brownish BC, test thin, loosely embedded in dorsal of AG, SV elongated, deeply embedded; CD (spermoviduct) joins soft white folds of MG and AG; HD thickened distinctly coiled and striated, connects AG to the yellowish granulated crescent shaped HG. The HG is positioned in right posterior of coelom under pallial cavity, to which the AG is distal and positioned under the digestive gland.

Spermatophore (Fig. 39F). Thread-like (length = 8.66 mm, n = 1), translucent, test thin; head section, bluntly rounded, body cylindrical, containing a white gelatinous mass, tapers along the transparent flagellum to a very thin tip; both sections smooth, featureless; head shorter, thinner than flagellum (head length = 3.37 mm; flagellum length = 5.32 mm; ~ 39% of SPM length; head width = 71 μm; flagellum width = 21 μm). Single SPM coiled embedded in brown gelatinous mass in one BC (LHI, AM C.546717 [SK052]).

Comparative remarks. Siphonaria exulum ( atra group, unit 47) is the sister species of a subclade containing four species, S. scabra, S. pravitas sp. nov., S. bourailensis sp. nov., and S. ouassensis sp. nov. All five species together form Clade B in the siphonariid tree (Figs 1, 2). Siphonaria exulum differs from other species by COI distances of ≥ 18.9% (Table S4). Siphonaria exulum has been found in sympatry with S. lentula on LHI, which has a shell with more prominent raised ribs, scalloped edge, and siphonal ridge with a flared end, darker interior, BD with distal loop, and SPM with a bulbous head. Siphonaria pravitas sp. nov. has more prominent and raised ribs on siphonal ridge, greater edge scalloping, darker interior, a shorter wider BD without a distal loop, a larger BC and a shorter SPM. Siphonaria exulum is the only known species in the Kermadec Islands. Siphonaria ouasseensis has a lower, paler, less evenly ribbed shell, a smaller, narrower AO, a more elongate and narrower CD, and a smaller BC, and S. bourailensis has a lower, less evenly and broader ribbed shell, more prominent siphonal ridge, a larger, broader AO, a more elongate and narrower CD, a larger HD, and a shorter SPM.

We found that the RS structures of specimens from NI correspond reasonably well with those of specimens from the Kermadec Islands especially in size and shape of the epiphallic parts, AO and HD (hermaphroditic parts may vary) (Figs 39E, G, H). Conchologically, the most similar species are S. mauiensis sp. nov. (Hawaii), S. griffithsorum sp. nov. (Mauritius), and S. tongatapuensis sp. nov. (Tonga).

Distribution and habitat. Known exclusively from Kermadec Islands, NI and LHI (Fig. 37). In this study, found to be common in sheltered rocky surfaces (e.g., crevices, hollows, pits) on exposed rocky shores, often in vertical positions, upper to mid littoral level; home scars apparent (Fig. 38T). Also found attached to shells of Scutellastra kermadecensis (Pilsbry, 1894) on Kermadec Islands (see Oliver, 1915: 547) and marine debris at LHI.