Mokumea gracilicostata Monsecour & Raines, 2024, sp. nov.

Mokumea gracilicostata sp. nov. Figures 3 A–F Type Material. Holotype LACM 3854, 3 Paratypes LACM 3855, 3 Paratypes MNHN-IM-2018-1780, 1 Paratype CKM, 2 Paratypes MSF fa179, all from type locality; 3 Paratypes LACM 3856, 2 paratypes MNHN-IM-2018-1781, 3 Paratypes CKM, 3 Paratypes MSF fa180, all from West side of Wilkes Island, 30–35 m. Type Locality. Wake Atoll, off northwest side of Wilkes Island, 19.2951 o N, 166.6009 o E, 25–30 m deep. Distribution. Only known from Wake Atoll, around Wilkes Island at depths of 25–35 m deep. Description. Shell rather small size for genus, up to 3.0 mm; fusiform, elongate. Protoconch paucispiral, of 1.4–1.5 smooth whorls. Transition to teleoconch weakly visible. Teleoconch of 2.9–3.1 whorls, relatively smooth; suture slightly impressed.Axial sculpture of only weak close-set ribs. Spiral sculpture absent apart from basal cords, extending to mid-apertural height. Aperture narrow, 55–60% of shell height. Outer lip slightly thickened, smooth. Inside with sinus on adapical end and 6–7 denticles, diminishing in strength toward abapical end. Columellar callus thick, slightly raised, not denticulate, with V-shaped incision deep in aperture. Parietal callus thick. Siphonal canal short, open, slightly recurved. Teleoconch whorls pale yellowish with white subsutural spiral band and zigzag-pattern of thin brown lines. Protoconch brown, translucent. Aperture white; columella translucent white with brown zigzag-pattern visible. Radula not studied. Height of holotype: 2.5 mm. Remarks. Mokumea gracilicostata is most similar to Mokumea albovittata (Lopes, Coelho & Cardoso, 1965) (fig 3 G) from Brazil, with which it shares the paucispiral protoconch and same color pattern. However, M. gracilicostata differs from M. albovittata by its smaller size, narrower aperture and presence of fine axial ribs, while M. albovittata is smooth. Mokumea gracilicostata also differs from Mokumea fuscolineata (Thiele, 1930) (fig 3 H) from Australia being smaller in size, having paucispiral protoconch, narrower aperture and color pattern with greater number of brown zigzag lines. The three species of Mokumea occurring in Japanese waters: M. albomarginata (Okamoto & Habe, 1979) (fig 3 I), M. divaricata (Pilsbry, 1904) (fig 3 J) and M. yuhitai (Habe, 1991) (fig 3 K) all have paucispiral protoconchs. However, M. gracilicostata differs by its smaller size, wider shell with less convex whorls, narrower aperture and color pattern with greater number of brown zigzag lines. Etymology. Latin adjectives gracilis, thin and costatus, ribbed, in reference to the numerous, fine axial ribs.