Sinum striotis, Simone, 2024

Genus Sinum Röding, 1798 View in CoL Sinum striotis new species

( Fig. 10 View Figure 10 ) https://zoobank.org/ A7F9DB82-3787-443B-AADE-21530989400B

Sinum sp. Brazil: Simone, 2011: 168, 214, appendix 2.

Types: Holotype MZSP 32260 View Materials , ♀ . Paratype: BRAZIL. São Paulo; Santos , off, 24°25′41″S 45°54′14″W, 50-60 m, MZSP 32166 View Materials , 1♂ (fishermen, o.t., iv.1999) GoogleMaps .

Type locality: BRAZIL. São Paulo ; between Queimada Grande Island and Lage de Santos Island, 24°25′10″S 46°24′06″W, 30-35 m [fishermen, o.t., xii.1998] GoogleMaps .

Diagnosis: Brazilian species with more flattened shell. Sculpture delicate, with narrow and uniform lines, gradually increasing from periphery up to suture. Radula rachidian not so inclined inwards, central cusp much small- er, and all cusps blunt. Penis retractile, but robust, with thick muscular walls, with small papilla at tip.

Description: Shell ( Fig. 10-G View Figure 10 ) of ~ 40 mm, highly discoid, aperture very ample. Color white, periostracum light yellow to beige, deciduous in older portions ( Fig. 10C, G View Figure 10 ). Outline elliptic, ~1.4× longer than wide; flattened, ~2.6 times longer than tall; up to 3.5 whorls. Spire plane to weakly convex, occupying ~¼ of dorsal surface ( Fig. 10C, G View Figure 10 ). Protoconch of 1 whorl, smooth, planar, simple ( Fig. 10D, J View Figure 10 ), of ~ 1 mm; located in middle of right-posterior quadrant of dorsal surface. Penultimate whorl sculptured by 22-24 spiral low, delicate, uniform lines, interspaces equivalent to their width; spiral lines uniformly growing up to last whorl, covering entire dorsal surface; ventral surface only possessing well-marked growth lines, commarginal with peristome inner lip. Suture planar, but visible. Periphery with rounded edges ( Fig. 10A, E View Figure 10 ). Aperture occupying ~60% of inferior region, glossy, outer lip simple, amply convex; inner lip also simple, symmetrically concave to outer lip ( Fig. 10B,F View Figure 10 ). Callus relatively well-developed, white, planar, with inferior expansion running along ~20% of inner lip, tapering up to fusing with inner lip ( Fig. 10B, F View Figure 10 ), posterior edge forming narrow umbilicus.

Radula ( Fig. 10H View Figure 10 ) with rachidian occupying ~ ⅓ of radular ribbon width, ~3× wider than long, central half rectangular, with distal edge possessing trapezoidal, thick projection, strongly curved inwards; in its tip 3 blunt cusps, being central cusp smaller than lateral cusps; rachidian central half still having pair of basal, lateral, blunt cusps articulating with neighbor tooth; rachidial lateral ¼ of each side as oblique projections. Lateral pair of teeth slightly narrower than rachidian, base flattened, twice longer than wide; tip relatively thick, with internal expansion; distal edge with blunt central larger cusp and 2 smaller cusps in each side. Marginal teeth elongated slightly curved inwards, mainly close to tip; both occupying ~ ⅕ of rachidian width in each side, inner and outer marginal similar with each other, inner with about double of outer teeth width,more flattened,and with subterminal small cusp in inner edge (absent in outer marginal); both with blunt tip.

Penis ( Fig. 10I View Figure 10 ) totally retractile inside penial cavity (ph). Vas deferens (vd) thick, convolute, running inside haemocoel, opening in penis tip. Penis broad, short, with thick-muscular walls. Tip with transverse aperture, flanked by papilla (pp) in a side.

Etymology: The specific epithet is based on the Latin word striatis, meaning stria, and otis, meaning ear; being the shell looking like a striated ear.

Distribution: Amapá to Santa Catarina, Brazil.