Siphonaria madagascariensis Odhner, 1919

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 : 125

Siphonaria madagascariensis Odhner, 1919

( Figs 46G–I, 47H–I)

Siphonaria madagascariensis Odhner 1919: 20 , pl. 1, figs 10–12 (type locality: Majunga [Mahajunga, Madagascar]).— Dautzenberg 1923: 24; Hubendick 1945: 29, fig. 50; 1946: 55, pl. 4, figs 20–24; White & Dayrat 2012: 65.

Material examined. Type material. Lectotype of Siphonaria madagascariensis Odhner, 1919 , present designation, from Majunga [ Mahajunga , Madagascar]; coll. M.W. Kaudern, 1912 ( UUZM UUMS 2000 ). Two paralectotypes, same data as lectotype ( UUMS; not seen).

Other, non-type material. Madagascar: Ambatobe , Bavarama, 25°27.9’S, 44°57.6’E, BM06 , ( MNHN IM-2009-14095 p [M582]); Plage de Lavanono, 25°25.2’S, 44°56.3’E, BM01 (MNHNIM-2009-13779p[M577]) ; SW coast, Itampolo , Fringing reef, 24°50.885’S, 43°59.693’E MA09-1 a ( AM C.585971 10p, AM C.584818 d [M267, SK372]; C.584819 p [M268, SK370], C.584820 p [M269, SK371]); Inner lagoon shore, 24°50.885’S, 43°59.693’E MA09-1 b ( AM C.608184 7p, C.584957 p [M270], C.584958 [M271], C.584959 p [M272]).

Taxonomic remarks. The largest syntype is herein designated as the lectotype of S. madagascariensis for the stabilisation of the name (Art. 74.1 of the Code). Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes ( Fig. 46G–I) and geographic series of additional specimens (Table S1). Morrison (1972: 56–58) treated S. madagascariensis as a junior synonym of S. laciniosa based on similarity in shell form and ‘common reproductive development’. This synonymy is not supported by examination of type specimens and comparative morpho-anatomy.

External morphology. Foot wall, mantle, cephalic folds and pneumostomal lobe all evenly pale cream in colour paler to foot edge, darker to foot sole; faint irregular dark brown pigmentation markings over foot wall and centre of cephalic folds; mantle narrower than foot wall, lobed with a thickened cream edge band; mantle lobes align with undulations of primary shell ribs, foot wall and pneumostome pustulose, pneumostome wide between right ADMs and within mantle.

Shell ( Figs 46G–I; Table S9). medium sized (max sl mean = 19.3 mm, SD = 2.1 mm, n = 6), ovate, flattened, shell height low, apex offset strongly to left and posterior of centre, apical sides convex, growth lines prominent, surface uneven; protoconch direction heterostrophic (n = 1), shell whorl dextral; growth striae distinct; ribs raised, whitish, wavy rib count (mean = 42.7, SD = 1.6, n = 6), ridges rounded, width increases strongly to shell lip, rib interstices narrow, dark brown; 11–14 prominent primary ribs, extend up to 1mm beyond shell edge; siphonal ridge prominent, formed by dual primary ribs, 1–2 interspersed secondary ribs; shell lip uneven, weakly scalloped and unevenly corrugated aligning with protruding ribs. Interior colouration matches white primary ribs and dark brown rib interstices, from shell lip, over shell margin to the dark chocolate brown coloured spatula; ADM scar impression distinct, same as shell margin colouring, siphonal groove prominent, indented; CMS straight to convex; thickening / faint whitening of shell interior occurs; white layering thickens and covers shell margin, spatula coated white (e.g., Fig. 46G).

Reproductive system ( Fig. 47H; 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 over back of BM. Join of AO and ED to top of GA distinct, AO larger than GA, elongated, broad, bluntly pointed, slightly bent, much thicker than ED; ED longer and narrower than AO; AO, GA and ED all muscular white tissue; EG large, bluntly pointed with a single long broad bent flagellum F1; BD and CD connect in opposing directions into GA, CD at inner side and BD in front of ED entry; BD with bulbous entry and weak distal loop, in front of GA / ED join, BD and CD similar in thickness, BD longer, both ducts smooth and pass together through RAM connecting into MG ( BD over CD), BC large, bulbous, embedded in MG / AG and against digestive tract; HD long broad coiled, links under digestive tract against foot sole, a small broad AG to a separated broad yellowish granulated HG, MG small, AG and MG folded, soft white tissue, AG slightly smaller than curved HG reflecting the close positioning to curvature of inner foot wall at right posterior quarter of coelom; SV embedded on left side of AG close to BC.

Spermatophore ( Fig. 47I). Thread-like, test thin, translucent (length = 10.96 ± 4.5 mm, n = 4, mean AL = 9.4 mm); head section cylindrical, bulbous, centrally bent, rounded tip; test thin, smooth, featureless, translucent, contains a white core, tapers into short flagellum; head slightly shorter, wider than translucent flagellum (head length = 8.5 ± 1.7 mm, ~ 82% of SPM length, head width = 155 ± 20 μm, flagellum width = 47 ± 10 μm, n = 4); 8 SPMs tightly coiled in BC of one specimen.

Radula. Dentition formula 30:1:30 ( Hubendick 1946: 56).

Comparativeremarks. Siphonariamadagascariensis ( atra group, unit 44) differs from its sister species S. belcheri ( Figs 1, 2) by COI distances of ≥ 21.4% (Table S5). Siphonaria madagascariensis occurs in sympatry with two other congeners in Madagascar: Siphonaria striata sp. nov. has a smaller, taller, paler shell with a more posteriorly offset apex, less raised ribbing and darker interior, distal and bursal BD loops, a smaller BC and a wider ED. Siphonaria itampoloensis sp. nov. has a smaller, taller, paler shell with less raised ribbing, a smaller AO and BC, and a shorter ED. Based on comparatively ‘greater number of [shell] ribs’ and ‘stouter genital retractor’, Hubendick (1946: 56) doubted that S. madagascariensis should be ‘specifically distinguished’ from S. kurracheensis . However, apart from being genetically clearly different, S. madagascariensis has consistently broader and larger RS epiphallic parts (including genital retractor) than S. kurracheensis .

Distribution and habitat. Endemic to Madagascar ( Fig. 48). Found in sheltered positions on moderately exposed fringing reef and inner lagoon shores, mid littoral level.