Siphonaria planucosta, 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 : 172-174

Siphonaria planucosta sp. nov.

( Figs 68D–E, L–N, 69C–D)

Material examined. Type material. Holotype, from Dolokoan Beach , 8°31.424’S, 125°37.091’E, N of Dili, Timor-Leste; coll. B.W. Jenkins, TL01-1, 14 July 2019 ( AM C.584826 [M446, SK229 (RS + SPM)], Fig. 68D) . Paratypes: same data as holotype ( AM C.585443 10+p, C.585442 p [M451, SK165], Fig. 68E) .

Other, non-type material. Timor-Leste: Dolokoan Beach N of Dili, 8°31.424’S, 125°37.091’E TL01-1, ( AM C.585925 p [SK231]) .

External morphology. Foot sole dark grey, foot edge cream; foot wall, cephalic folds and pneumostomal lobe evenly grey; black pigment shading at join of foot wall and mantle, concentrated over cephalic folds; mantle thin, narrower than foot wall, edge lobed with black bands aligning with shell rib interstices and interstice width; pneumostome under mantle between right adductor muscles.

Shell ( Figs 68D–E, L; Table S9). Small sized (max sl mean = 8.3 mm, SD = 0.47 mm, n = 2), ovate; low, fragile, thin; apex offset strongly posterior and to left, apical sides strongly convex, protoconch direction weakly homostrophic to central (n = 1, Fig. 68L),below apex, curls to posterior, shell whorl dextral; growth striae indistinct, shell edge uneven, faintly scalloped; rib count (mean = 33, SD = 4, n = 2), primary ribs flat, pale white, fairly straight bent in places, broaden to shell lip, 2–3 secondary ribs between primary ribs, interstices dark brown; paired primary ribs form siphonal ridge, usually not prominent, may appear raised, protoconch area darker; Interior shell margin white, dark chocolate brown rays extend from shell lip to spatula appearing paired, aligning under rib interstices; spatula and indistinct siphonal groove evenly dark chocolate brown; ADM scar indistinct, CMS convex; thickening of shell lip occurs, infills and reduces lip scalloping. Shell resembles other small dark normalis group.

Reproductive system ( Fig. 69C; n = 2). Positioned within entire right side of coelom, against foot wall on foot muscle, under the respiratory cavity and intestine occupying large proportion of animal body volume; epiphallic parts positioned over BM. GA medium, with singular GP through foot wall; AO very small, narrow, bluntly pointed, joined to lower ED and upper GA; ED very short, broad, centrally bent, joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG very large, soft whitish tissue, slightly folded, joins ED; single very broad flagellum (F1), similar length and width to ED, appears as an extension of ED, EG and F1 joined in parallel; BD and CD connect side-by-side into GA between ED join and GP, both ducts short, slightly bent, smooth, thickened, whitish, featureless, pass closely together between outside RAM and inner foot wall ( BD over CD) into soft white folded tissues of MG; MG / AG complex medium in size; CD connecting to ducts, BC embedded in folds close to embedded blackish SV; BD without distal loop and MA, with loop immediately prior to BC; BC relatively large, spherical, thin whitish translucent test, (4 SPM in holotype AM C.584826 TL01- 1 [M446, SK229]); HD short, narrow, coiled, links ducts in soft white folded tissues of AG to yellowish granulated HG; outer edge of MG lobbed; AG larger than HG, sides match curvature of inner foot wall.

Spermatophore ( Fig. 69D). Broad head with short flagellum (length = 1.71 ± 0.08 mm, n = 2); head section cylindrical, bulbous, rounded tip; test thin, smooth, featureless, translucent encasing a white opaque central core; short looped tapering section merges head to filamentous flagellum; head slightly shorter, wider than translucent flagellum (head length = 1.16 ± 0.17 mm, flagellum length = 0.55 ± 0.088 mm, ~ 68% of SPM length, head width = 119 ± 8 μm, flagellum width = 11 ± 0 μm, n = 2); 4 SPMs tightly coiled in BC ( AM C.584826 holotype [M446, SK229]).

Comparative remarks. In our mitochondrial phylogeny ( Figs 1, 4), S. planucosta sp. nov. ( normalis group, unit 79) is the sister species of S. radiata (unit 12). Siphonaria planucosta sp. nov. differs from S. radiata by COI distances of ≥ 18.4% (Table S8).

We found S. planucosta sp. nov. in sympatry with five congeners in TL. For comparisons with S. forticosta sp. nov., S. alba , S. javanica , S. viridis , and S. campestra sp. nov. refer to comparative remarks under these species.

Distribution and habitat. Recorded from Dolokoan Beach, N of Dili, Timor-Leste ( Fig. 70). In this study, found at sheltered positions (mainly in crevices) on exposed shore boulders, at mid littoral levels ( Fig. 68L).

Etymology. From ‘planus’ (Latin = level, even), for the level, even primary ribs on the shell of this species; adjective.