Siphonaria christmasensis, 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 : 146-147

Siphonaria christmasensis sp. nov.

( Figs 53I–J , 54H–J, Q–R )

Siphonaria ‘sp. 1’— Wells & Slack-Smith 2000: 113; Tan & Low 2014: 367.

Material examined. Type material. Holotype, from E side Smith Point , Flying Fish Cove , 10°25.749’S, 105°39.957’E, CI; coll. B.W. Jenkins, CI01-1/2, 11 Sept 2018 ( AM C.595957 [M298], Fig. 54H ), 23 paratypes, same data as holotype ( WAM S74040 p [SK069], Fig. 54I , WAM S74075 9p; AM C.585992 9p, AM C.584837 p [M299], AM C.584838 p [M300], AM C.584839 p [M301]); Ethel Beach , 10°27.827’S, 105°42.497’E; coll. B.W. Jenkins, CI02-1, 11 Sept 2018 ( AM C.584846 p [M308], Fig. 54J ).

Other, non-type material. Australia, CI: Off Dale 3, 10°28.52’S 105°33.503’E ( AM C.595955 p [SK566]); E side Smith Point Flying Fish Cove, 10°25.749’S, 105°39.957’E CI01-1 ( AM C.584836 p [SK021 protoconch A11], C.585319 p [SK071 protoconch C1], C.585321 p [SK083], C.585954 p [SK568]), CI01-2 ( AM C.584729 10p); West White Beach, 10°27.748’S, 105°34.934’E CI01-3 ( AM C.585922 p [SK567]); Ethel Beach, 10°27.827’S, 105°42.497’E CI02-1 ( AM C.585695 8p, C.584846 p [M308]) .

Taxonomic remarks. This species has previously been identified as ‘ Siphonaria sp. 1 ’ by Wells & Slack-Smith (2000: 113).

External morphology ( Fig. 54R ). Foot sole grey, foot wall grey to yellowish with black flecked pigmentation; edge of foot sole and foot wall yellowish to white, fading to grey at mantle join; mantle lobed, translucent, narrower than foot wall, patches of black pigmentation occur on lobes, aligning with dark shell rib interstices; cephalic folds grey with black flecks concentrating around lobe join; foot wall and pneumostome pustulose, pneumostome yellowish, wide, within mantle, between right ADMs.

Shell ( Figs 54H–I, Q ; Table S9). Small (max sl mean = 10.1 mm, SD = 1.4 mm, n = 11); height low to medium; ovate; apex offset posterior and left, apex cap brown, often eroded to appear white; apical sides convex, posterior concave; protoconch direction central to weakly homostrophic (n = 2; Fig. 54Q ), shell whorl dextral; growth lines distinct, undulating; rib count (mean = 30.6, SD = 6.3, n = 11), 20–30 primary ribs prominent, often very broad, weakly raised, whitish, straight to weakly bent, width increases strongly to shell lip often touching to replace rib interstices and any infill of 0–1 secondary ribs, extend slightly beyond shell edge creating corrugations and weak scalloping in the uneven shell lip; rib interstices black to dark brown, siphonal ridge slightly raised, indicated by abutting paired primary ribs; segments either side of siphonal ridge often clear of primary ribs, black or brown coloured, show finer secondary ribs; interior shell margin yellowish, white under primary ribs, dark black/brown markings under rib interstices span from shell lip to spatula across the shell margin; spatula brown to dark brown; ADM scar impression distinct, same as shell margin colouring, cephalic scar convex; thickening of shell lip commonly occurs, translucent, not covering black/brown markings of rib interstices, CMS curved.

Reproductive system ( Fig. 53I; n = 2). Positioned within coelom under the respiratory cavity, 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 large elongated centrally twisted, tapers to point, joined to upper GA alongside ED; ED long broad slightly centrally bent, joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG large pointed soft whitish tissue, slightly folded, joins ED; single short flagellum (F1) on side. BD and CD join side-by-side into GA between AO join and GP; CD short curved smooth thickened whitish featureless; BD long, narrower than CD, with distal loop and prominent MA; both 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 similar thickness to CD; BC small bulbous thin whitish translucent test; HD short narrow coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; AG larger than HG, both outer sides curved to curvature of inner foot wall.

Spermatophore ( Fig. 53J ). Test thin, translucent (length = 11.27 mm, n = 1, AL = 7.21 mm; possibly longer as flagellum appeared incomplete); head bulbous, tip bluntly rounded, containing a white gelatinous mass; very short taper region into the filamentous transparent flagellum; both sections smooth, featureless; head shorter and much thicker than flagellum (head length = 4.94 mm, ~ 44% of SPM length, head width = 126 μm, flagellum width = 32 μm); single SPM found in one BC ( AM C.585321).

Comparative remarks. In our mitochondrial phylogeny ( Figs 1 , 3 ), S. christmasensis sp. nov. ( plicata group, unit 63) is the sister species of S. delicata sp. nov. (unit 62). Both species occur on CI forming a well-differentiated lineage. They differ from each other by COI distances of ≥ 10.7% (Table S7). We found this species in sympatry with five congeners on CI: For comparisons with S. alba , and S. incerta refer to comparative remarks under these species. Siphonaria tenebrae sp. nov. has a slightly larger, lower, darker shell with greater edge scalloping, a single primary rib forming the siphonal ridge, darker interior, a more pointed AO and a longer F1. Siphonaria umbra sp. nov. has a slightly larger, lower and darker shell, a larger AO and BC, and a longer F1. Siphonaria delicata sp. nov. has a smaller, taller, darker shell with less prominent ribs, darker interior, a larger AO and BC, and longer ED and F1.

Distribution and habitat. Known only from CI, Indian Ocean ( Fig. 55 ). In this study, found in sheltered positions on moderately exposed and exposed limestone rocky shores, upper and mid littoral levels ( Fig. 54R ).

Etymology. For the type locality, Christmas Island, Indian Ocean.

Figures

FIGURE 1. Maximum Likelihood phylogram based on analyses of a concatenated sequence data set of 16S and COI. Branches are collapsed at the species level. Branch labels give unit numbers and accepted species names. Numbers on branches indicate branch support employing 10,000 ultrafast bootstraps.Available genus-group names are shown next to their type species. Scale bar indicating modelled sequence divergence.

FIGURE 3. Maximum Likelihood phylogram (partial, species not collapsed). Clades J–L (laciniosa and plicata groups) of the tree shown in Fig. 1. Branch labels give specimen identifiers for new sequences or Genbank accession numbers for imported sequences from other studies and geographic regions (see Tables S1–S2 for details). Identical haplotypes are merged into single tips. Numbers on branches indicate branch support by employing 10,000 ultrafast bootstraps. Clade names give unit numbers and accepted species names. Scale bar indicating modelled sequence divergence.

FIGURE 53. Reproductive morphology of S. jeanae, S. campestra sp. nov., S. camura sp. nov., S. caubianensis sp. nov and S. christmasensis sp. nov. A–B. S. jeanae, WA, Rottnest Is, AM C.585820 [SK215]. C–D. Holotype of S. campestra sp. nov., Timor- Leste, Dili, AM C.584823 [M447, SK230]. E–F. Holotype of S. camura sp. nov., Okinawa, Tancha Bay, AM C.585614 [M491, SK310]. G–H. S. caubianensis sp. nov., Philippines, Polillo Is, WAM S113803 [M600, SK557]. I. Holotype of S. christmasensis sp. nov., CI, Flying Fish Cove, AM C.595957 [M298]. J. CI, AM C.585321 [SK083]. Scale bars = 1 mm.

FIGURE 54. Shells of S. campestra sp. nov., S. caubianensis sp. nov., S. christmasensis sp. nov. and S. costellata sp. nov. A–C, M–N. S. campestra sp. nov., Timor-Leste, Dili. A. Holotype AM C.584823 [M447, SK230]. B. Paratype AM C.585354 [SK266]. C. Paratype AM C.585355 [SK267]. M. In situ. N. Animal. D–E, O–P. S. camura sp. nov., Okinawa, Tancha Bay. D. Holotype AM C.585614 [M491, SK310]. E. Paratype AM C.584920 [M490, SK309]. O. In situ. P. Protoconch, AM C.585613 [SK510]. F–G. S. caubianensis sp. nov., F. Philippines, Caubian Is., holotype AM C.595933 [SK560]. G. Philippines, NW Polillo Is, WAM S113803 [M600, SK557]. H–J, Q–R. S. christmasensis sp. nov., CI, Flying Fish Cove. H. Holotype AM C.595957 [M298]. I. Paratype WAM S74040 [SK069]. J. Paratype, Ethel Bch AM C.584846 [M308]. Q. Protoconch AM C.585319 [SK071], R. CI, in situ. K–L, S–T. S. costellata sp. nov. K. Singapore, Lazarus Island, Holotype AM C.585236 [M416, SK100]. L. Paratype AM C.585226 [M338]. S. Protoconch, AM C.585233 [SK099]. T. In situ. Unlabelled scale bars 10 mm.

FIGURE 55. Known occurrence records of S. camura sp. nov., S. caubianensis sp. nov., S. christmasensis sp. nov., S. costellata sp. nov., S. delicata sp. nov., S. forticosta sp. nov. and S. gemina sp. nov.