Siphonaria opposita
Creators: name: Jenkins, Bruce
name: Köhler, Frank
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Siphonariida
Siphonariidae
Siphonaria
Siphonaria opposita

description: Siphonaria opposita (Iredale 1940)
(Figs 46D–F, R–T, 47C–G)
Siphonaria siquijorensis — Hedley 1909: 369 (not S. siquijorensis Reeve, 1856).
Mallorisiphon oppositus Iredale 1940: 440 (type locality: Keppel Bay, [Qld, Australia]).— Short & Potter 1987: 122; White & Dayrat 2012: 66, 70.
Siphonaria (Siphonaria) atra var. oppositus — Hubendick 1946: 52.
Siphonaria (Siphonaria) savignyi — Hubendick 1955: 2 (not S. savignyi Krauss, 1848).
Siphonaria oppositus — Cernohorsky 1972: 210.
Siphonaria ‘ atra group, unit 34’— Dayrat et al. 2014: 264, fig. 5L.
Material examined. Type material. Lectotype of Mallorisiphon oppositus Iredale, 1940, present designation, from Keppel Bay, [Qld, Australia]; coll. H. Bernhard [1940] (AM C.103714, Fig. 46D). Four probable paralectoypes from North Keppel Is, [Qld]; coll. H. Bernhard, [1 Jan 1934] (AM C.108527).
Probable paralectotype of Mallorisiphon oppositus Iredale, 1940 from Emu Park, Keppel Bay, Qld. Pres. T. Iredale, 22 May 1953 ‘Paratype’ (MV F13839)
Other, non-type material. PNG: Kranket Is, N end, Madang, 5°11’S, 145°51’E (AM C.595915 p [SK545], C.595916 p [SK544]); Biliau I., 05°11.8’S, 145°48.2’E, PM38 (MNHN IM-2013-15195 p [M560]). Australia, Qld: W side Kissing Pt, Townsville, 19°14.332’S, 146°48.040’E, Q26-2 (AM C.585150 p [M189]); Mackay breakwater wall, 21°06.415’S, 149°14.033’E, Q14-2 (AM C.584998 d [R21282]); Yeppoon, Wreck Pt, 23°08.736’S, 150°45.865’E, Q08-4 (AM C.585598 4p, C.585135 p [M424,SK237],C.585136p[M425],C.585137p[SK237]), Double Head, 23°09.908’S, 150°47.638’E, Q08-3 (AM C.585701 8p); Buff Pt, 23°11.123’S, 150°47.830’E, Q08- 2 (AM C.585597 4p, C.585860 p [SK113], C.585867 p [M210], C.585868 p [M211]); Zilzie, 23°16.778’S, 150°49.553’E, Q08-1 (AM C.585343 p). Canoe Pt Gladstone 23°56.155’S, 151°21.964’E, Q07-2 (AM C.585671 6p, C.585865 p [M212], C.585866 p [M213]); Bagara, Hervey Bay, 24°49.180’S, 152°28.011’E, Q06- 1 (AM C.585700 8p, C.585129 p [SK180]); Urangan, Hervey Bay 25°17.504’S, 152°54.664’E, Q05-1 (AM C.585341 1p, C.585864 p [M209]); Scarborough, Nth Reef, 27°11.432’S, 153°06.755’E, Q03-5 (AM C.585126 p [SK136]); 27°11.451’S, 153°06.722’E, Q03-4 (AM C.585596 4p); 27°11.589’S, 153°06.892’E, Q03-6 (AM C.585637 5p, C.585819 p [M458, SK181], C.585863 p [M431, SK135]), Drury Pt, Q 03-7 (AM C.585409 10+p), Scarborough Pt, 27°12.168’S, 153°06.980’E, Q03-8 (AM C.585670 6p).
Taxonomic remarks. Iredale (1940: 440) stated in the original description that M. oppositus was collected ‘from many places in Qld’. The description was evidently based on more than one specimen and did not contain a type designation. Therefore, all types are syntypes. The largest syntype labelled ‘holotype’ (Fig. 46L) is herein designated as the lectotype of M. oppositus for the stabilisation of the name (Art. 74.1 of the Code). Through this designation, the type locality is herein restricted to Keppel Bay, Qld.
Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes (Fig. 46E–F) and geographic series of additional specimens (Table S1). Hubendick (1946: 52) and Cernohorsky (1972: 210) incorrectly treated S. opposita as a synonym of S. atra. However, the figured specimen of ‘ S. atra ’ in Cernohorsky (1972: 210, pl. 60, fig. 1) is a specimen of S. vudaensis sp. nov. Morrison (1972: 56–58) treated ‘ Mallorisiphon oppositus ’, as a synonym of S.laciniosa based on similarity in shell form and ‘common reproductive development’. This synonomy is not supported by examination of type specimens and comparative morpho-anatomy.
External morphology (Fig. 46R). Foot sole, foot wall, foot edge, cephalic folds and pneumostomal lobe evenly cream; mantle thick translucent in larger specimens, thin in smaller specimens, edge thickened, whitish, lobed, with very light black pigmentation at mantle edge aligning with large primary rib interstices; 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, centrally black pigmented cephalic folds; pneumostomal lobe long, under the mantle, unpigmented, behind right cephalic fold.
Shell (Figs 46D–F, R, T; Table S9). Medium sized (max sl mean = 20.8 mm, SD = 1.9 mm, n = 11), ovate; height very low; apex offset central and strongly to left, apical sides convex to straight, protoconch direction homostrophic (n = 1; Fig. 46T), shell whorl dextral; growth striae prominent, without radial banding, exterior often evenly light brown, whitened if eroded; shell thickness thin to thickened; rib count (mean = 50, SD = 3.7, n = 11), 17–21 primary ribs pale, fairly evenly spread radially, narrow, raised and protrude strongly (often> 1mm) beyond shell lip to unevenly scallop and corrugate the edge; 1–2 distinctly smaller, finer secondary ribs between primary ribs; rib interstices slightly darker; dual slightly spaced primary ribs over siphonal ridge, slightly more prominent, protruding more than other primary ribs, interstice gap wider either side of siphonal ridge. Interior; shell margin dark brown to white, narrow white rays align on grooves over shell margin under primary ribs, weakly furrowed, extend from lip to spatula; siphonal groove distinct, bent, same colour as shell edge; spatula evenly dark chocolate brown to mottled tan, ADM scar distinct, CMS convex, similar colour shell margin; thickening of shell lip commonly occurs, infills interior rib furrows and margin reducing lip scalloping, spatula not whitened.
Reproductive system (Fig. 47C, F; n = 4). HG / AG / MG complex positioned within right side of coelom, against foot wall over foot muscle, under the respiratory cavity; epiphallic parts relatively large, positioned between BM and RAM; GA small indistinct, with singular GP through foot wall; AO large broad elongated pointed, joined to upper GA; ED short, broad, coiled, twisted, joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG large, longer than ED, soft whitish tissue, folded, joins ED; single short broad flagellum (F1), shorter and narrower than ED, appears as an extension of ED; BD and CD connect from opposite directions into GA between ED join and GP, distal loop in BD, both ducts long straight smooth thickened whitish featureless, pass closely together through RAM (BD over slightly wider CD) into soft white folded tissues of MG; MG / AG complex relatively large; BC embedded in folds of AG / MG complex close to embedded blackish SV; BD with short distal twisted loop, twisted coiling immediately prior to BC, slightly thinner but much longer than CD; BC relatively small, bulbous, thin whitish translucent test; HD short wide coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; AG usually larger than HG.
Spermatophore (Figs 47D, E, G). Relatively short and wide (length = 6.37 ± 0.93 mm, n = 6), head section cylindrical, tip bluntly rounded, central white core; flagellum very thin, transparent, tapering to a thread-like end; both sections smooth, featureless;test thin, translucent (head length = 4.9 ± 0.76 mm, ~80% of SPM length, head width = 114 ± 20 μm; flagellum width = 14 ± 2 μm, n = 6); prominent twist before short taper region into filamentous transparent flagellum; three SPMs coiled, embedded in brown gelatinous mass in BC of two specimens.
Comparative remarks. Siphonaria opposita (atra group, unit 34) is the sister species of S. plana (unit 35); both species together are the sister group of S. denticulata (unit 33) (Figs 1, 2). Siphonaria opposita differs from S. plana by COI distances of ≥ 8.1% and from S. denticulata by distances of ≥ 15.8% (Table S3). Throughout its range, S. opposita has been found in sympatry with eight congeners: For comparisons with S. zelandica, S. denticulata, S. normalis, S. scabra, S. atra, S. viridis, and S. javanica refer to comparative remarks under these species. The specimen figured as ‘ atra group, unit 34’ in Dayrat et al. (2014: fig. 5L) exhibits features consistent with S. opposita. The shell of. S. opposita has frequently been mistaken for S. eumelas (= S. atra).
Distribution and habitat. Endemic to Qld, between Townsville and MacKay (Fig. 48). In this study, found on sheltered rocky shores, at upper to mid littoral level.
description: Published as part of 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), pp. 1-217 in Megataxa 13 (1) on pages 128-129, DOI: 10.11646/megataxa.13.1.1, http://zenodo.org/record/14984186