Siphonaria forticosta, 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

Siphonaria forticosta sp. nov.

( Figs 56D–F, P, 58E–F)

Material examined. Type material. Holotype, from Christi Rea Beach , 8°32.072’S, 125°36.868’E, Timor-Leste; coll. B.W. Jenkins, TL01-2, 14 July 2019 ( AM C.584829 p [M441, SK227], Fig. 56P) . Paratype, same data as holotype ( AM C.585318 p [SK546], Fig. 56E); two paratypes from Dolokoan Beach , 8°31.424’S, 125°37.091’E, N of Dili, Timor-Leste; coll. B.W. Jenkins, TL01-1, 18 July 2019 ( AM C.584825 p [M445], Fig. 56F, AM C.584830 p [SK228], Fig. 56P) .

Other, non-type material. Dolokoan Beach, 8°31.424’S, 125°37.091’E, N of Dili, Timor-Leste ( AM C.585981 8p, C.585991 p [SK547]) .

External morphology. Foot sole evenly cream; foot wall, foot edge, cephalic folds and pneumostomal lobe evenly grey cream, darker to foot edge, faint black pigmentation on foot wall; mantle thin, translucent, narrower than foot wall, edge weakly lobed, without pigmentation; cephalic folds small, pneumostome wide.

Shell ( Figs 56D–F, P; Table S9). medium to large sized (max sl mean = 15.6 mm, SD = 6.1 mm, n = 2), ovate; height medium to low; apex offset sightly posterior and central (usually eroded), apical sides convex, protoconch direction homostrophic (n= 1, Fig. 56P), shell whorl dextral; growth striae indistinct, shell thick; exterior evenly brown maybe mottled, juveniles display a mix of bluish colouration; rib count (mean = 36, SD = 1.0, n = 2), primary ribs weakly bent, raised and protrude beyond shell lip (up to 1 mm) to unevenly scallop the edge; interspersed with 1–2 finer secondary ribs; single or paired primary ribs form siphonal ridge. Interior shell margin dark brown to tan, spatula dark chocolate brown, white rays aligning under primary/secondary ribs extend irregularly from shell lip over margin, siphonal groove prominent, same colour as shell margin; ADM scar distinct, CMS straight, paler than shell lip; thickening of shell margin noted forming a translucent layer.

Reproductive system ( Fig. 58E; n = 2). Positioned within coelom under the respiratory cavity, hermaphroditic complex ( HG, AG and MG) to posterior against right foot wall and over foot sole, epiphallic parts positioned to anterior between RAM and BM; AO medium, elongated, blunt, weakly centrally bent, merges to upper part of indistinct GA, singular GP; ED short, wide, compressed in coil, longer than AO, joins to lower side of GA; GA, AO, ED all white muscular fibrous tissue; EG soft whitish, folded, smaller than AO; single very long twisted uneven thin flagellum (F1), tip of F1 tucks into gap between start of FI and EG; BD and CD jointly but opposing connections to side of GA between AO and GP; both ducts smooth and pass closely together through RAM ( BD over CD); BD long narrow with prominent short distal loop without MA to inner body wall, twist immediately prior to connection to medium sized bulbous BC with thin translucent test, embedded in lower folds of MG; CD short, wider than BD; CD connects into MG; HD short, thick, brown markings, coiled, under AG, links AG to much smaller yellowish granulated HG; MG and AG folded, soft white tissue.

Spermatophore ( Fig. 58F, J). Thread-like (length = 5.21 mm, 52 % of AL, n = 1); translucent, test thin; head section narrow, bluntly rounded, cylindrical, flagellum tapers to a thin tip, tip attached to inner test of BC; both sections smooth, featureless. Head section longer wider than flagellum (head length = 3.16 mm; ~ 61% of SPM length, head width = 70 μm, flagellum width = 17 μm, n = 1); 3 SPM tightly folded in yellowish gel in BC ( AM C.585991).

Comparative remarks. In our mitochondrial phylogeny ( Figs 1, 2), S. forticosta sp. nov. ( atra group, unit 71, Clade G) is the sister species of a sub-clade containing S. sirius , S. recurva sp. nov., S. incerta sp. nov. and an unidentified species from Tonga. It differs from these species by COI distances of ≥ 20% (Table S3). Siphonaria forticosta has been found in sympatry with six congeners in TL: For comparisons with S. javanica , S. viridis , S. campestra sp. nov., S. alba , and S. atra , refer to comparative remarks under these species. Siphonaria planucosta sp. nov. has a smaller, slightly darker shell with more prominent ribbing, weaker edge scalloping, and a smaller, narrower AO.

Distribution and habitat. Recorded from Dolokoan Beach, Timor-Leste ( Fig. 55). In this study, found at mid littoral level in sheltered positions (mainly in crevices) on exposed shore boulders.

Etymology. From contraction of ‘fortis’ (Latin = strong, sturdy) and ‘costa’ (Latin = rib), referring to the sturdy primary ribs on the shell of this species.