Siphonaria monticulus ( 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 : 129-130

Siphonaria monticulus ( Iredale, 1940)

( Figs 49A–C, O–P, T, 50A–D)

Hebesiphon monticulus Iredale 1940: 441 , pl. 34, figs 11–13 (type locality: Lifu [sic Lifou], Loyalty Islands, NC).— Hubendick 1945: 29; White & Dayrat 2012: 65.

Siphonaria (Siphonaria) monticulus — Hubendick 1946: 45, pl.3, figs 7–9.

Material examined. Type material. Lectotype of Hebesiphon monticulus Iredale, 1940 , present designation, from ‘ Lifu’ [Lifou], Loyalty Islands, NC; coll. 1905 ( AM C.103720 ‘holotype’, Fig. 49A) . Paralectotype, same data as lectotype ( AM C.410720 ) .

Other, non-type material. NC, Lifou: Drueulu, 20°55.570’S, 167°05.067’E LFU02-1 ( AM C.585397 10+p, C.585875 p [SK058], C.584948 p [M384], C.584949 p [M385], C.584950 p [M386], C.584951 p [M387]); We Baie de Chateaubriand East coast, 20°54.779’S, 167°15.636’E LFU01-1 ( AM C.584944 p [SK057], C.584945 p [SK056]) .

Taxonomic remarks. The original description does not contain a type designation. Hence all types are considered as syntypes. The specimen labelled as ‘holotype’ ( Fig. 49A) is herein designated as lectotype of H. monticulus for the stabilisation of the name (Art. 74.1 of the Code). This specimen is probably the shell figured in Iredale (1940: 441, pl. 34, fig. 11–13) and matches the shell dimensions given in the original description. The lectotype is a small specimen displaying a particularly tall shell profile. Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 49C) and geographic series of additional specimens (Table S1). While the description of S. monticulus in Hubendick (1946: 45) agrees with our concept of this species, the specimen figured from ‘Wijnkoopsbai, south coast of Java’ ( Hubendick 1946: pl. 3, figs 7–9) is not of H. monticulus . Moreover, Hubendick (1946) did not examine any specimens from Lifou, Fiji or Tonga. Hence, he has probably misidentified specimens of S. javanica .

External morphology ( Fig. 49T). Foot sole grey; foot wall, pneumostome, cephalic folds and mantle evenly cream; two small black epithelial eye spots centralised on two thick centrally touching cephalic folds; genital pore inconspicuous, located on foot wall posterior to right cephalic fold; mantle thin translucent extends to shell edge, edge weakly lobed with white band and light black bands aligning to rib interstices; pneumostomal lobe thin and within mantle between the right ADMs, closes the pneumostomal and anal openings at the mantle edge; light black pigmentation over centre of cephalic folds.

Shell ( Figs 49A–C, O; Table S9). Small sized (max sl mean = 12.56 mm, SD = 1.2 mm, n = 5), ovate; height medium to tall; apex offset central to sightly posterior, apical sides convex, protoconch direction central to weakly heterostrophic (n = 1; Fig. 49O), shell whorl dextral; growth striae distinct, exterior uneven, shell thickness thick; rib count (mean = 42.8, SD = 4.6, n = 5), no clear distinction between primary and secondary ribs, ribs pale white, fairly straight, rib interstices paler, mottled radial colouration band appears to be algal growth in hollows; increasingly raised and protrude slightly beyond shell lip, edge uneven weakly scalloped, strongly corrugated; 3–4 fused ribs form an indistinct siphonal ridge. Interior shell lip and margin white, dark to pale brown rays aligning under primary/secondary ribs, span shell margin to golden/whitish spatula, siphonal groove distinct raised above shell lip, same colour as shell edge/margin, ADM scar distinct, CMS straight, paler than shell lip; thickening of shell lip translucent, infills and reduces lip scalloping, spatula becomes whitened.

Reproductive system ( Figs 50A, C; n = 3). Positioned within and right side of coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned to anterior over BM against digestive organs; GA prominent with singular GP through foot wall; AO large, bluntly pointed, joined to upper GA alongside ED; ED elongated, broad, twisted and coiled (without prominent MA), joins to side of GA above BD; GA, AO, ED all white muscular fibrous tissue; EG large, soft whitish tissue, slightly folded, joins ED; single long thick flagellum (F1), similar length to ED, appears as a continuous extension of ED to EG, laid over BM; BD and CD connect close in opposing directions into GA between AO join and GP, BD with distal loop and prominent MA; both ducts long, straight, smooth, similar thickness of narrow, whitish, featureless, pass closely together through centre of RAM ( BD over CD) into soft white folded tissues of MG; MG / AG complex relatively large; BC embedded in folds of AG / MG close to embedded SV; BC large, flat rounded, thin translucent test; HD long, thickened, coiled, brown markings, links ducts in soft white folded tissues of AG to yellowish granulated HG; outer edge of MG lobbed; AG / MG much larger than HG.

Spermatophore ( Figs 50B, D). Thread-like, test thin, translucent (length = 13.09 mm, n = 1); head section cylindrical,tip bulbous bluntly rounded,containing a white gelatinous core, tapers into the filamentous transparent flagellum; both sections smooth, featureless; head longer and much thicker than flagellum (head length = 7.71 mm, n = 1; head ~58.8 % of SPM length; head width = 80 μm; flagellum width = 13 μm). Single SPM embedded in red-brown gelatinous mass in one BC ( AM C.584951).

Radula. Dentition formula 39:1:39 ( Hubendick 1946: 46).

Comparative remarks. Siphonaria monticulus ( plicata group, unit 57) represents a well-differentiated lineage. It is the sister species of a subclade containing S. lirata , S. tanguissonensis sp. nov., S. mauiensis sp. nov. and S. undans sp. nov. ( Figs 1, 3). S. tanguissonensis sp. nov. and S. lirata differ by COI distances of ≥ 15.4 % and ≥ 17%, respectively (Table S7). Siphonaria monticulus has been found in sympatry with three congeners on Lifou, Loyalty Islands: For comparison with S. normalis refer to comparative remarks under that species. Siphonaria hienghenensis sp. nov. has a larger, darker shell with a more prominent and flared siphonal ridge, stronger edge scalloping, a shorter ED, narrower BD, smaller BC, and a less thread-like SPM. Siphonaria bourailensis sp. nov. has a lower, darker shell with more prominent and fewer primary ribs, and a shorter ED and F1. Siphonaria monticulus exhibits a shell morphology similar to that other species of the plicata group, such as S. nuttallii (Hawaii), S. tongatapuensis sp. nov. ( Tonga), S. lirata ( Guam), S. plicata (Lifou) , S. namukaensis sp. nov. ( Fiji), and S. yagasaensis sp. nov. ( Fiji). A specimen from Java figured as ‘ S. monticulus’ in Hubendick (1946: 91, pl. 3, fig. 7–9) is a misidentification of S. javanica .

Distribution and habitat. Endemic to Lifou, Loyalty Islands, NC ( Fig. 48). In this study found in sheltered positions (e.g., hollows of rocky platforms, cliff bases) on exposed rocky shores, mid and lower littoral levels ( Fig. 49P).