Siphonaria gemina, B. W. Jenkins & Köhler, 2024

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 : 149-153

Siphonaria gemina sp. nov.

( Figs 56G–T, 57A–B, 58G–J, 59A–D)

Siphonaria cf normalis — Maes 1967: 119, pl. 14, fig. l; Wells 1994:

19; Tan & Low 2014: 367 (not S. normalis Gould, 1846 ). Siphonaria normalis — Willan et al. 2015: 330 (not S. normalis

Gould, 1846 (not 1856)). Siphonaria sp. — Wells & Bryce 1995: 113; 1996: 63. Siphonaria ‘ atra group, unit 51’— Ossenbrügger et al. 2023: 38,

fig. 2a–b.

Material examined. Type material. Holotype, from Nightcliff 12°22.836’S, 130°50.402’E, Darwin, NT; coll. B.W. Jenkins, NT23-1, 8 Sept 2017 ( AM C.585485 [M088, SK089], Fig. 56G) . Paratype, from Cox Peninsula 2, 12°25.558’S, 130°44.593’E; coll. B.W. Jenkins, NT25- 2, 10 Sept 2017 ( AM C.585487 p [M089], Fig. 56H), 2 paratypes, from Native Point oyster reef, Dundee Beach 12°42.906’S, 130°20.653’E , NT; coll. B.W. Jenkins, NT26-6, 11 Sept 2017 ( AM C.585096 p [M140], AM C.585099 p [M141]) .

Other, non-type material. Australia, Qld : Sweers Is , 12°03.456’S, 96°52.329’E, Q56-2 ( AM C.585188p [M091]). NT: Luxmore Hd, Melville Is, 11°20.639’S, 130°23.149’E, NT24-1 ( AM C.585336 p); Nightcliff, Darwin, 12°22.836’S, 130°50.402’E NT23-1 ( AM C.585090 p [SK078 protoconch C5], C.585091 p [SK089]); Cox Peninsula 2, 12°25.558’S, 130°44.593’E NT25-2 ( AM C.585092 p [M144], C.585093 p [M145], C.585094 p [M090, SK091], C.585098 p [M143]); N of Native Point, Dundee Beach, 12°42.182’S, 130°20.881’E NT26-1 ( AM C.585095 p [SK103], C.585337 p [SK088]); Native Point oyster reef, Dundee Beach, 12°42.906’S, 130°20.653’E NT26-6 ( AM C.585097 p [M094]); Native Point reef, Dundee Beach, 12°42.981’S, 130°20.807’E NT26-3 ( AM C.585488 p [M146]). WA: Tait Point, Mission Bay, 14°05.442’S, 126°41.143’E, WA04-1 ( AM C.584669 p [SK246]; Raft Point Collier Bay, 16°04.045’S, 124°26.814’E, WA17-2 ( AM C.584668 p [M464, SK199]); CatamaranBay, 16°27.622’S, 123°00.242’E,WA22-3 ( AM C.585301p[M071, SK090],C.585302 p[M072],C.585303 p [M043]); Cape Keraudren, 19°57.393’S, 119°46.358’E, WA29-2 ( AM C.585308 p [M032]) . Mauritius: Nth Albion Is, Mauritius, 20°12.258’S, 57°24.252’E, MRU2- 2 ( AM C.584971 [M249], Fig. 56I, C.585976 20p, AM C.584972 p [M250], Fig. 56J) . Australia, CKI: E coast of Home Is, 12°06.917’S, 96°53.835’E, CKI04-1 ( WAM S74044 [M317, SK255], Fig. 56K, AM C.608183 15p, C.584666 p [M318], C.584667 p [M319]); S coast of West Is , 12°12.210’S, 96°50.372’E, CKI02-2 ( AM C.584849 p [M315], Fig. 56L, C.584850 p [M316]); West Island , N point (Trannies), 12°08.540’S, 96°49.013’E, CKI01- 1 ( AM C.585372 10p); S coast of West Is , 12°12.210’S, 96°50.372’E, CKI02-2 ( AM C.585373 10p, C.584665 p [M314], C.585933 p [SK092], C.585942 p [SK086]); N coast Direction Is, 12°03.456’S, 96°52.329’E, CKI03-1 ( AM C.585374 10p, C.585941 p [SK535]). Marquesas Islands : Nuku Hiva, Baie des Controleurs, 08°53.92’S, 140°02.92’W, MQ7-M ( MNHN IM-2013-74895 [M574], Fig. 57A), Baie d’Hakatea, 08°56.53’S, 140°09.69’W, MQ25-M, ( MNHN IM-2013-74904 p [M566], Fig. 57B; IM-2013-74902 p [M571], IM-2013-74900 p [M576], IM-2013-74903 p [M572], MNHN IM-2013-74901 p [M573]), Baie des Controleurs, 08°53.92’S, 140°02.92’W, MQ7- M ( MNHN IM-2013-67892p [M578], IM-2013-74894 p [M575], IM-2013-74896 p [M564]) .

External morphology ( Fig. 56M). Foot sole and foot wall evenly pale yellowish grey, paler at foot/wall edge; foot wall and mantle more yellowish, without black pigmentation; mantle strongly lobed, translucent, as wide as foot wall, covers exposed inner shell lip; 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 unpigmented cephalic folds; pneumostomal lobe long, under the mantle, unpigmented, between the right ADMs.

Shell ( Fig. 56G–T, 57A–B; Table S9). Shell ribbing and colouration variable; small sizing (max sl mean = 9.3 mm, SD = 1.7 mm, n = 8); ovate to elongate, height medium; apex often tall, pointed (protoconch very tall when intact), slightly offset posteriorly and left; protoconch direction heterostrophic (n = 2; Fig. 56T) to upright (n = 2; Fig. 56Q), shell whorl dextral; apical sides weakly convex, posterior concave; protoconch area distinctly darker brown, growth lines usually distinct undulating; rib count (mean = 28, SD = 5.3, n = 8), primary ribs white, curved, wavy, moderately flare at and extend beyond shell edge, rib ridges rounded, rib interstices dark brown/black; paired primary ribs form siphonal ridge, extend well beyond line of shell lip, strongly to weakly flared upwardly at shell edge; none to one secondary ribs between primary ribs, either side of siphonal ridge the number of secondary ribs greater; interior shell lip uneven, corrugated to no corrugations, shell lip with white blotches or rays under primary ribs, dark brown/ black under rib interstices; white rays may extend over shell margin; spatula usually evenly dark brown/black but may be white to dull white; siphonal groove usually white, may be dark brown/black, bounded on either side by prominent dark brown/black axial patches aligning with primary rib interstices. WA and NT specimens often with heavy and strongly raised ribbing with corrugations on shell lip, CKI specimens possess flatter ribs and few to no corrugations on shell lip; thickening of inner shell lip and spatula not observed.

Reproductive system ( Fig. 58G, I, 59A; n = 5). Positioned within coelom under the respiratory cavity, occupies the entire right side of coelom, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned to anterior between BM and RAM; GA small, with singular GP through foot wall; AO very small, bluntly pointed, joined to upper GA alongside ED; ED short, broad, slightly bent (without prominent MA), joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG large, soft whitish tissue, slightly folded, joins ED; single narrow flagellum (F1; possible 2 nd flagellum), similar length and width to ED, appears as a continuous extension of ED to EG, laid over BM, often centrally bent; BD and CD connect together into GA between ED / AO joint and GP, both ducts short, straight, smooth, thickened, whitish, featureless, pass closely together through 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; BD on posterior side only, unlooped, similar thickness to CD; BC relatively large, spherical, thin translucent test; HD short, not thickened, coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; outer edge of MG lobbed; AG much larger than HG, sides match curvature of inner foot wall.

Spermatophore ( Fig. 58H, J, 59B). Broad head with short flagellum (length = 4.0 ± 2.9 mm, 64% of AL, n = 4), head section cylindrical, bulbous, centrally bent, rounded tip; test thin, smooth, featureless, translucent encasing a white opaque central core; short tapering section merges head to filamentous flagellum; head shorter, wider than translucent flagellum (head length = 1.8 ± 0.18 mm, ~ 82% of SPM length, head width = 171 ± 14.8 μm, flagellum width = 24 ± 1.3 μm, n = 4); 1 SPM coiled in one BC ( AM C.585488). The SPM of specimens from Mauritius differs somewhat in having a shorter flagellum ( Fig. 58J, length = 4.34 ± 3.42, n = 3, AM C.584971). Specimens from the Cocos (Keeling) Islands have a broad head with short flagellum (length = 5.8 ± 3.2 mm, n = 2), head section cylindrical, bulbous, centrally bent, rounded tip; test thin, smooth, featureless, translucent encasing a white opaque central core; short tapering section merges head to filamentous flagellum; head shorter, wider than translucent flagellum (length = 4.0 ± 2.1 mm, ~ 69% of SPM length, head width = 249 ± 20.2 μm; flagellum width = 29 ± 2.1 μm, n = 4); 1–2 SPM in each of two BC ( WAM S74044 , AM C.585942).

Comparative remarks. In our mitochondrial phylogeny ( Figs 1, 4), S. gemina populations from northwestern Australia, CKI, Mauritius, and the Marquesas Islands form a clade with little apparent genetic differentiation between them ( normalis group, unit 78). COI sequences of this unit differ from each other by genetic distances of up to 6.2% (Table S8). We observed minor, yet consistent morphological differences between populations from mainland Australia, Mauritius, the Marquesas Islands, and the Cocos Keeling Islands in features of the shell, BC, and SPM. However, we consider these differences to represent intraspecific morphological variation. Siphonaria gemina sp. nov. is the sister species of an unidentified Siphonaria sp. (unit 11, from NT, Australia and Yap Is). These two clades differ by COI distances of ≥ 14.1% (Table S8). Throughout its range in tropical WA, we found S. gemina gemina in sympatry with five congeners: For comparisons with S. alba , S. normalis , S. zelandica , and S. viridis refer to comparative remarks under these species. Siphonaria restis sp. nov. has a larger, lower, sturdier shell with a less prominent siphonal ridge, stronger edge scalloping, a larger AO and BC, longer ED and BD, and a shorter SPM. Specimens figured as ‘ Siphonaria unit 51’ by Ossenbrügger et al. (2023) belong to the same MOTU, unit 78 and correspond well with specimens examined here.

Distribution and habitat. Siphonaria gemina has a wide distribution spanning Mauritius, the Seychelles, the Cocos (Keeling) Islands, Tropical Australia, between Cape Keraudren in northern WA and the Sweers Is, Gulf of Carpentaria, Qld, to the Marquesas Islands ( Fig. 55). In this study, found on moderately exposed rocky shores, in upper littoral level ( Fig. 56S).

Etymology. From ‘geminus’ (Latin = paired), referring to the prominence of paired siphonal primary ribs accentuated by dark flanking bands on the shell of this species; adjective.