Swainsonia, H. ADAMS & A. ADAMS, 1853

GENUS SWAINSONIA H. ADAMS & A. ADAMS, 1853 View in CoL

( FIGS 28B, C, 29G–I)

Type species: Mitra fissurata Lamarck, 1811 ; by typification of replaced name ( Mitrella Swainson, 1831 non- Risso, 1826).

Synonym: Mitrella Swainson, 1831 (not Risso, 1826). Type species: Mitra fissurata Lamarck, 1811 ; SD, Cossmann (1899: 152).

Diagnosis: Shell small to medium sized (15–65 mm), fusiform or elongate-biconical, weakly sculptured and often polished in appearance. Protoconch narrowly conical, of about three smooth, weakly convex, whorls. Spire ortho- or cyrtoconoid, spire whorls evenly convex to flattened; suture distinct, impressed. Sculpture of regular, shallow and widely spaced punctate spiral grooves, either covering the entire shell surface, or limited to the adapical whorl portion, or lacking entirely. Axial sculpture usually not developed or, when present, consisting of numerous, fine and low, rounded folds, developed on the spire but indistinct on the periphery of the last adult whorl. Shell base typically with convex outline, continuing into short and stout, deeply notched, siphonal canal. Siphonal fasciole indistinct or moderately developed. Aperture elongate, narrow to moderately wide. Outer aperture lip straight or gently evenly convex adapically; anterior edge of outer lip strongly convex, sometimes slightly drawn abapically. Inner lip with four to five fine or strong, subequal columellar folds. Shell light brown, orange or white, typically with intricate scalelike pattern of fine light or white lines. Scabricola - type radula with comb-like rachidian bearing six long, slen- der cusps, the four central ones notably exceeding the two marginal ones ( Fig. 28B, C). Lateral teeth with very strong, robust cusp, giving tooth the appearance of a tin-opener, the serrate inner surface of tooth bearing three to four weaker cusps. Base of laterals with curved upper margin, forming a socket interlocking laterals of adjacent rows.

Distribution: Indo-Pacific, upper subtidal depths, on sand.

Species included: Swainsonia biconica Bozzetti , 20113, S. casta (Gmelin, 1791) 1, S. ekerae Cernohorsky , 19733, S. fissurata (Lamarck, 1811) 2, S. fusca (Swainson, 1824) 1, S. limata (Reeve, 1845) 3, S. newcombii (Pease, 1869) 3, S. ocellata ( Swainson, 1831) 3.

Remarks: Many contemporary authors have treated Swainsonia as a subgenus of Scabricola ( Cernohorsky, 1970, 1991; Pechar, Prior & Parkinson, 1980; but see Poppe & Tagaro, 2008), but our results indicate that it should be elevated to full genus. This treatment of Scabricola and Swainsonia , however, contradicts the phylogenetic hypothesis implied by radular morphology. The typical Scabricola radula (as described by Cernohorsky, 1970) is present in Scabricola variegata , Swainsonia fusca and Swainsonia casta , while the radulae of Scabricola desetangsii and S. olivaeformis show a divergent morphology.