Siphonaria delicata, 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 : 148-149

Siphonaria delicata sp. nov.

( Figs 56A–C, M, 58C–D)

Material examined. Type material. Holotype, from Ethel Beach 10°27.827’S, 105°42.497’E, Christmas Is, Indian Ocean; coll. B.W. Jenkins, CI02-1, 11 Sept 2018 ( AM C.585322 [M421, SK108], Fig. 56A).

Five paratypes, same data as holotype ( AM C.585585 2p, WAM S74043 p, WAM S74041 p [M307], Fig. 56C, WAM S74042 p [M410], AM C.608199 p [SK093], Fig. 56B) .

External morphology. Animal evenly pale cream without any dark/black pigmentation; paler at foot/ wall edge; mantle wider than foot wall, weakly lobed, translucent, covers exposed inner shell lip, outer edge thickened; genital pore indistinct, located on foot wall to right anterior of right cephalic fold; two small black epithelial eye spots centralised on two centrally touching cephalic folds; pneumostomal lobe long, under the mantle, unpigmented, between the right ADMs.

Shell ( Figs 56A–C; Table S9). size small (max sl mean = 8.5 mm SD = 1.0 mm, n = 4), ovate, shell thin translucent; tall, apex offset to posterior; protoconch below height of apex, direction heterostrophic (n = 2), protoconch area distinctly dark brown to black; anterior apical side convex, posterior side concave, lateral apical sides straight to weakly concave; growth lines prominent; rib count (mean = 29.3, SD = 4.8, n = 3) primary ribs pale to dark grey, weakly raised, secondary ribs not prominent, 1–2 between primary ribs, rib interstices dark brown to black; siphonal ridge not prominent, shell lip even, weakly corrugated with some primary rib ridges; interior polished, shell lip apically banded with white rays aligning with primary ribs extending and narrowing over shell margin and ADM scar to the start of dark chocolate brown spatula; CMS weakly concave, similar but darker colouration to spatula and shell margin; thickening of inner shell lip occurs in larger specimens, resulting in white coating covering the brown/black colouration of inner shell lip.

Reproductive system ( Fig. 58C; n = 2). Positioned within entire right side of coelom, against foot wall on foot muscle, under the respiratory cavity occupying large proportion of animal body volume. GA, EG and ED positioned between BM and RAM. GA small, with singular GP through foot wall; AO distinct, bluntly pointed, maybe elongated, joined to upper GA alongside ED; ED long, broad, centrally bent, joins to side of GA; GA, AO, ED all white muscular fibrous tissue; EG medium, soft whitish tissue, slightly folded, joins ED; single very long flagellum (F1), similar length and width to ED, appears as an extension of ED, possible F2. BD and CD with opposing connections into GA between ED join and GP, CD short,; BD long, both ducts smooth, thickened, whitish, featureless, pass closely together through RAM ( BD over CD) into soft white folded tissues of MG; MG / AG complex relatively large; BC embedded in folds close to embedded SV; BD with distal loop(s) and MA, longer thinner than CD; BC relatively large, spherical, thin whitish translucent test; HD short, wide, coiled, links ducts in soft white folded tissues of AG to small, yellowish granulated HG; outer edge of MG lobbed; AG larger than HG, both left outer sides curved to curvature of inner foot wall.

Spermatophore ( Fig. 58D). Test thin, translucent (length = 5.77 ± 1.23 mm, n = 2); over half-length comprises a translucent cylindrical head section (head length = 4.73 ± 0.79 mm, ~ 49% of SPM length, n = 3); tip bluntly rounded, containing a white gelatinous core mass; tapers into a filamentous transparent flagellum; head section much thicker than flagellum (head width = 59 ± 1.2 μm, flagellum width = 11 ± 0 μm, n = 3), both sections smooth, featureless; 6 and 3 SPM each in holotype and paratype .

Comparative remarks. In our mitochondrial phylogeny, S. delicata sp. nov. ( plicata group, unit 62) is the sister species of S. christmasensis sp. nov. ( Figs 1, 3). Both differ from each other by COI distances of ≥ 10.7% (Table S7). For comparison with S. christmasensis sp. nov. refer to comparative remarks under that species. We found this species in sympatry with four other congeners on CI: For comparisons with S. alba , and S. incerta refer to comparative remarks under these species. Siphonaria tenebrae sp. nov. has a lower, darker shell with greater edge scalloping and raised ribbing, a smaller AO and BC, and a shorter ED. Siphonaria umbra sp. nov. has a slightly larger, taller shell with a dual-ribbed siphonal ridge, a shorter ED, and a slightly shorter SPM.

Distribution and habitat. Known only from CI, Australia, and likely endemic to this island ( Fig. 55). In this study, found in sheltered positions on exposed rocky shores, at upper littoral level ( Fig. 56M).

Etymology. From ‘delicata’ (Latin = delicate) for the small, delicate shell; adjective.