Siphonaria costellata, Jenkins, Bruce & Köhler, Frank, 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 : 147-148

Siphonaria costellata sp. nov.

( Figs 54K–L, S–T, 58A–B)

Siphonaria guamensis — Tan & Chou 2000: 115, fig 115; Tan & Woo 2010: 61; Tan & Yeo 2010: 294 (not S. guamensis Quoy & Gaimard, 1833 ).

Siphonaria sp. — Swennen et al. 2001: 142, fig. 522.

Siphonaria ‘ normalis group, unit 13’— Dayrat et al. 2014: 259, 260, 267, fig. 3O.

Material examined. Type material. Holotype, from Lazarus Island , causeway 01°13.288’N, 103°51.195’E, Singapore; coll. Chim C.K. and B.W. Jenkins, SI04-3, 21 Nov 2018 ( ZRC.MOL.24890 [M416, SK100], Fig. 54K). 18 paratypes, same data as holotype ( AM C.585234 p [M326], AM C.585427 10p, AM C.585677 6p), paratype from Lazarus Island, 01°13.355’N, 103°51.148’E, Singapore; coll. B.W. Jenkins, SI04-2, 24 Nov 2018 ( AM C.585226 p [M338], Fig. 54L).

Other, non-type material. Australia, Qld : Weipa, 12°37.795’S, 141°51.853’E, Q52-1 ( AM C.585186 p [M075]; C.585187 p [M178]); Inspection Pt, Sweers Is, 17°08.471’S, 139°36.868’E, Q56-3 ( AM C.585189 p [M147]) . NT: Nhulunbuy , Cape Wirawawoi, 12°09.513’S, 136°46.904’E, NT05-1A ( AM C.585529 20+p, C.585075 p [SK044], C.585076p [M028], C.585077 p [M092]); East Woody Islet, 12°09.695’S, 136°45.075’E, NT05- 2 ( AM C.585684, 7p); N Turtle Beach, 12°18.816’S, 136°55.930’E, NT04-1 ( AM C.585477 17p; C.585990 10+p); Smith Pt 2, 11°07.466’S, 132°08.538’E, NT21- 3 ( AM C.585989 10+p) . Singapore: Pasir Ris , seawall, 01°22.981’N, 103°56.956’E, SI01-1 ( AM C.585986 10p); Fort Road , drain seawall, 01°17.605’N, 103°53.809’E, SI01-3 ( AM C.585603 3p); Lazarus Island , 01°13.355’N, 103°51.148’E, SI04-2 ( AM C.585988 16p); Lazarus Island causeway, 01°13.288’N, 103°51.195’E, SI04- 3 ( AM C.585226 p [M338], C.585233 p [SK099], C.585234 p [M326], C.585236 p [M457, SK183], C.595973 p [M327]); Lazarus Island channel headland, 01°13.085’N, 103°51.429’E, SI04-4 ( AM C.585985 10p) .

External morphology. Foot sole, foot wall and cephalic folds evenly dark yellowish grey, paler at foot/ wall edge; foot wall and mantle more yellowish; mantle lobed with small black pigmentation at thickened edge aligning with rib interstices; 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 spots centralised on two centrally touching unpigmented cephalic folds; pneumostomal lobe relatively long, under the mantle, unpigmented, between the right ADMs.

Shell ( Figs 54K–L, S; Table S9). Medium to large sized (max sl mean = 11.6 mm, SD = 1.7 mm, n = 7), ovate; medium to tall; apex offset central sightly posterior (usually eroded), apical sides strongly convex, protoconch direction heterostrophic (n = 2; Fig. 54S), shell whorl dextral; growth striae prominent in bands, shell thickness thick; rib count (mean = 45.7, SD = 5.5, n = 7), primary ribs pale white, fairly straight, increasingly raised and protrude beyond shell lip to unevenly scallop and corrugate the edge; 1–2 interspersed pale white finer secondary ribs, rib interstices darker; paired primary ribs on siphonal ridge, no more prominent than other primary ribs. Interior shell margin dark brown to tan, white rays align on shell margin under primary/secondary ribs, siphonal groove distinct, same colour as shell edge, points to right anterior; spatula dark chocolate brown to mottled tan; ADM scar distinct, CMS straight, paler than shell lip; thickening of shell lip translucent, infills and reduces lip scalloping, spatula becomes whitened.

Reproductive system ( Fig. 58A; n = 1). Positioned within right side of coelom, against foot wall on foot muscle, under the respiratory cavity; epiphallic parts positioned between RAM and BM. GA very small indistinct with singular GP through foot wall; AO small broad bluntly pointed, joined to GA; ED elongated narrow thickened, slightly centrally bent, joins to GA; GA, AO, ED all white muscular fibrous tissue; EG large, soft whitish tissue, folded, joins ED; single wide flagellum (F1) lays over BM, shorter but similar width to ED, appears as an extension of ED. BD and CD connect side-by-side to GA between AO and GP, both ducts thick short bent smooth whitish, pass together through RAM ( BD over thicker CD) into soft white folded tissues of MG, BC embedded in folds close to embedded blackish SV; BD short narrow bent before BC, without distal loop or MA to inner anterior foot wall; CD shorter wider than BD; BC relatively large bulbous, thin whitish translucent test (2 SPM in brownish gelatinous mass of BC); MG / AG complex relatively large; HD short narrow coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; AG / MG larger than HG, both outer sides curved to curvature of inner foot wall.

Spermatophore ( Fig. 58B). Relatively short (length = 4.25 ± 0.196 mm, n = 2, flagellum incomplete), test thin, translucent, containing a white gelatinous core mass; over half-length comprises a translucent bulbous cylindrical head section (head length = 1.646 mm, SD = 0.213 mm, n = 2; mean ~ 39% of SPM length, SD = 3%); tip bluntly rounded, with a prominent twist before tapering into a filamentous transparent flagellum; head section much thicker than flagellum (head width = 116 ± 16 μm, flagellum width = 12 ± 0 μm, n = 2); both sections smooth, featureless; 7–8 SPM tightly coiled in one BC ( AM C.585236).

Comparative remarks. In our mitochondrial tree ( Figs 1, 4, Clade E), S. costellata sp. nov. ( normalis group, unit 13) is more closely related to four species, S. normalis , S. madangensis , S. fuliginata , and S. campestra . It differs from any of these by COI distances of ≥ 7.3%. Throughout its range, this species has been found in sympatry with four congeners.Three species are sympatric in northern Australia, from N Qld to Nhulunbuy, NT: For comparisons with S. viridis , S. atra , and S. normalis refer to comparative remarks under these species. In Singapore the species is sympatric with S. viridis and S. alba ; refer to comparative remarks under these species. Siphonaria madangensis sp. nov. differs in having a smaller, lower shell, a smaller AO, larger BC, and a more bulbous SPM. The specimen identified as ‘ normalis group, unit 13’ in Dayrat et al. (2014: 266, fig. 3O) is a member of S. costellata .

Distribution and habitat. Recorded from Thailand, Singapore, Malaysia and NT, Australia ( Fig. 55). In this study, found in sheltered and vertical positions on moderately exposed rocky shores across upper littoral levels ( Fig. 54T).

Etymology. From ‘costellata’ (Latin = ribbed), referring to the finely ribbed shell; adjective.