Siphonaria tenebrae, 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 : 186

Siphonaria tenebrae sp. nov.

( Figs 74K–L, S–T , 75I–J )

Siphonaria ‘ laciniosa group, unit 38’— Dayrat et al. 2014: 264, fig. 5U (in part).

Material examined. Type material. Holotype, from Ethel Beach 10°27.827’S, 105°42.497’E, Christmas Is, Australia, Indian Ocean; coll. B.W. Jenkins, CI02- 1, 11 Sept 2018 ( AM C.584664 , [M305, SK256], Figs 74K, T ) . Paratype: E side Smith Point Flying Fish Cove 10°25.749’S, 105°39.957’E, Christmas Is, Indian Ocean; coll. B.W. Jenkins, CI01-2, 9 Sept 2018 ( WAM S74050 [SK120], Fig. 74L ) .

Other, non-type material. Christmas Is: E side Smith Point Flying Fish Cove , 10°25.749’S, 105°39.957’E CI01-2 ( AM C.585979 p, C.585980 p [SK413]) .

Externalmorphology ( Fig.74T ).Footedge,footwall, mantle, cephalic folds and pneumostomal lobe all yellow in colour with indistinct darker pigmentation markings; foot sole darker yellow to grey; mantle translucent, wider than foot wall, wider over anterior, strongly lobed with a thickened edge, tips of the major and minor mantle lobes align under primary ribs, wide bands of dark grey pigmentation align under the dark brown colouration of rib interstices; mantle lobes large, mould/extend to cover area of shell lip and align with undulations of primary shell ribs; pneumostome narrow, positioned between right adductor muscles and within mantle.

Shell ( Figs 74K, L ; Table S9). Small to medium sized (max sl mean = 17.6 mm, SD = 1.9 mm, n = 2), elongate ovate; height very low; apex offset to posterior and left, apical sides concave, protoconch direction undetermined, shell whorl dextral; growth striae indistinct, shell thin; rib count (mean = 28.5, SD = 1.5, n = 2), exterior evenly dark chocolate brown, pale white where rib ridges eroded, ribs straight, ridges rounded, larger broaden to and protrude beyond shell lip to strongly scallop and weakly corrugate the edge, some ends squared off; smaller secondary ribs fill gaps between primary ribs, rib interstices narrow; bent paired primary ribs on siphonal ridge. Interior evenly dark chocolate brown, some off-white rays under outer ends of primary ribs, siphonal groove shallow distinct; ADM scar distinct, CMS straight; thickening of shell lip not observed.

Reproductive system ( Fig. 75I; n = 3). Positioned against inside of foot muscle and foot wall on the right side within coelom, under the respiratory cavity. GA, EG and ED positioned between BM and RAM. AO small, bluntly pointed, joins to larger GA with singular GP; ED relatively long, broad, straight, much larger than AO, joins to upper GA; GA, AO, ED all white muscular fibrous tissue; EG small soft whitish with single wide adjacent flagellum (F1) appearing as an extension of ED and of similar length; BD and CD jointly but in opposing positions connect to GA between AO and GP; BD with a prominent distal loop and large MA to inner body wall is longer and slightly thinner than CD; both ducts smooth, relatively long and pass closely together through outer side of RAM ( BD over CD); CD connects into MG; BC small, bulbous, with thin translucent test, embeds in lower folds of MG / AG close to SV; HD short, bulbous, orange coloured, coiled, links AG to a smaller, yellow/ orange,granulated HD; MG and AG large, folded, soft white tissue; AL = 11.78 mm.

Spermatophore ( Fig. 75J ). Body cylindrical, elongate (length = 11.8 mm, AL = 13 mm, n = 1); test thin, translucent; head tip bluntly rounded, wide, evenly cylindrical, containing a core white gelatinous mass, tapers along the transparent flagellum to a thin tip; both sections smooth, featureless. Head section longer, much wider than flagellum (head length = 6.7 mm, n = 1; ~ 56% of SPM length, head width = 103 μm, flagellum width = 17 μm); SPM tightly coiled, embedded in whitish gelatinous mass [SK413].

Comparative remarks. In our mitochondrial phylogeny ( Figs 1 , 2 ), S. tenebrae sp. nov. ( atra group, unit 92) is the sister species of S. subatra (unit 38). Both species differ by COI distances of ≥ 15.1% (Table S3). Both species also differ in shell characteristics, RS structure, and external morphology. Siphonaria tenebrae has been found in sympatry with five congeners on CI: Siphonaria umbra sp. nov. has a less scalloped shell edge, more raised and prominent ribs, a paler interior with a darker spatula, and a larger AO and BC. For comparisons with S. alba , S. incerta , S. christmasensis sp. nov., and S. delicata sp. nov. refer to comparative remarks under these species.

Distribution and habitat. Known distribution endemic to CI, Australia, Indian Ocean ( Fig. 78 ). In this study, found in sheltered positions on moderately exposed and exposed limestone rocky platforms, at mid littoral levels ( Fig. 74S ).

Etymology. Derived from Latin noun ‘tenebrae’ meaning ‘dark’, referring to the evenly dark interior of the shell for this species.

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 2. Maximum Likelihood phylogram (partial, species not collapsed). Clades G–I (atra group) 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 (seeTables 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 spread over two pages.

FIGURE 74. Shells of S. tagaqaensis sp. nov., S. tanchaensis sp. nov., S. tanguissonensis sp. nov. and S. tenebrae sp. nov. A–C, M. S. tagaqaensis sp. nov., Fiji, Viti Levu. A. Holotype AM C.584852 [M275]. B. Paratype AM C.584854 [SK287]. C. Paratype AM C.584855 [SK297]. M. In situ. D–F, O–P. S. tanchaensis sp. nov. D–E. Okinawa, Tancha Bay. D. Holotype AM C.585615 [M495, SK314]. E. Paratype AM C.584912 [SK386]. F. Okinawa, Onna, paratype AM C.584913 [M505, SK326]. O. Onna, animal. P. Tancha Bay, in situ. G–J, N, Q–R. S. tanguissonensis sp. nov., Guam, Tanguisson Beach. G. Holotype AM C.584877 [M417]. H. Paratype AM C.584875 [M342]. I. Paratype AM C.584878 [M438, SK163]. J. Paratype AM C.584881 [SK253]. N. In situ. Q. Protoconch, AM C.584882 [SK141]. R. Animal. K–L, S–T. S. tenebrae sp. nov., CI, Point Flying Fish Cove. K. Holotype AM C.584664 [M305, SK256]. L. Paratype WAM S74050 [SK120]. S. In situ. T. Animal. Unlabelled scale bars 10 mm.

FIGURE 75. Reproductive morphology of S. tagaqaensis sp. nov., S. tanchaensis sp. nov., S. tanguissonensis sp. nov. and S. tenebrae sp. nov. A–B. Holotype of S. tagaqaensis sp. nov. AM C.584852 [M275, SK182]. C–D. S. tanchaensis sp. nov., Okinawa. C. Paratype AM C.584913 [M505, SK326], Tancha Bay. D. Onna, AM C.595924 [SK538]. E–H. S. tanguissonensis sp. nov., Guam, Tanguisson Beach. E–F. Holotype AM C.584877 [M417, SK102]. G–H. Paratype AM C.584878 [M438]. I–J. S. tenebrae sp. nov., CI, Ethel Beach. I. Holotype AM C.584912 [M305, SK256]. J. Paratype WAM S74050 [SK413]. Unlabelled scale bars = 1 mm.

FIGURE 78. Known occurrences of S. tenebrae sp. nov., S. poindimiensis sp. nov., S. umbra sp. nov., S. undans sp. nov., S. vudaensis sp. nov., S. waikoloaensis sp. nov. and S. yagasaensis sp. nov.