Scaphander gracilis Watson, 1883: 345−346; Watson, 1886: 645−646, pl. 47, figs 4a–c; Pilsbry, 1893: 247−248, pl. 31, figs 19−20; Dautzenberg & Fischer, 1896: 402; Locard, 1897: 47–49, pl. 1, figs 15–18; Bouchet, 1975: 338, pl. 3, fig. i; Eilertsen & Malaquias, 2013a: 404−405, figs 2.10; 14.
Scaphander gracilis var. minor Locard, 1897: 47–49.
Scaphander gracilis var. major Locard, 1897: 47–49.
Type material. Western Azores, south of Flores Island (38°30 ʹ N, 31°14 ʹ W; 1829 m), 4 syntypes (images seen; https://data.nhm.ac.uk/object/80cd6292-170e-4636-9c32- 859ad933b36e/1631750400000), lectotype and paralectotypes here designated (lectotype: H = 13.5 mm; paralectotypes: H = 8.8, 5.1, 11.3 mm), NHMUK 1887.2.9.2183–2186; Azores, south of São Miguel Island (37°26 ʹ N, 25°13 ʹ W; 1829 m), 2 syntypes (images seen; Natural History Museum 2014), specimens designated here as paralectotypes, NHMUK 1887.2.9.2187–2188 (H = 13.0, 14.4 mm) (Eilertsen and Malaquias 2013a); 1 syntype (image seen), here designated as paralectotype, NMINH 1899.114.182 (H = 14 mm).
Other material examined. Azores, between Santa Maria and São Miguel Islands (37° 10.820 ʹ N, 025°11.750 ʹ W − 37°10.368 ʹ N, 025°12.957 ʹ W; 2065 − 2066 m), 1 spc. dissected and sequenced for the mitochondrial gene COI, DBUA 1630, H = 20 mm.
Revised diagnosis. Shell solid, white, pyriform. Parietal callus thick, white, smooth, can present an angular hump around aperture inflexion point. Spire concealed. Outer lip protruding posteriorly beyond apex. Spiral sculpture composed of medium and small punctuated striations. Prostate cylindrical, prostatic duct short, narrower than prostate. Penial chamber lined with soft longitudinal grooves. Penial papilla absent.
Shell (Figure 1). Maximum H = 24 mm (Locard 1897). Shell solid, white, pyriform, covered by thin white to pale yellow periostracum. Parietal callus thick, white, smooth, can present an angular hump around aperture inflexion point. Spire concealed. Outer lip protruding posteriorly beyond apex in small wing. Spiral sculpture composed of regular lines of small or medium-sized punctuations.
Radula (Figure 2 (a)−(c)). Radular formula 15 × 1.1.1. Lateral teeth hook-shaped, curved, with weak denticulation on inner edge. Small rachidian teeth tetragonal, with expanded outward corners, straight or curved.
Digestive system (Figure 2 (d)−(e)). Salivary glands long with uneven surface. Paired gizzard plates subtriangular to kidney-shaped; unpaired gizzard plate thinner, elongated.
Reproductive system (Figure 2 (f)−(g)). Prostate elongate, cylindrical, narrowing towards penial chamber. Prostatic duct short, narrower than prostate, separating prostate from penial chamber. Penial chamber cylindrical, lined with soft longitudinal ridges running from genital opening to prostatic duct. Penial papilla absent.
Ecology. Feeds on foraminifera, agglutinating and non-agglutinating, ingested along with sand and mud (Figure 3). Live specimen collected between 2065 − 2066 m (present study), empty shells records between 1299 − 2995 m (Watson 1883; Dautzenberg and Fischer 1896; Locard 1897; Bouchet 1975; Eilertsen and Malaquias 2013a).
Distribution. Only known from the Archipelago of the Azores, where it is reported west and southwards of Flores Island, on the western slope of the mid-Atlantic ridge (Watson 1883) and eastwards of the Islands of São Miguel and Santa Maria, on the eastern side of the mid-Atlantic ridge (Watson 1883; Dautzenberg and Fischer 1896; Locard 1897; Bouchet 1975; present study).