(Figs. 33–34)
Type material: Holotype MNRJ 30287 [1] OP I # 3 (22 ° 35 'S, 39 ° 58 'W – 22 ° 32 'S, 39 ° 56 'W), 20.94 mm, 1620–1623 m. Paratype IBUFRJ 16460 [1] OP I # 9 (22 ° 41 'S, 40 °02'W – 22 ° 39 'S, 40 °01'W), 14.34 mm, 1609–1621 m. Paratype MNHN [1] OP I # 9 (22 ° 41 'S, 40 °02'W – 22 ° 39 'S, 40 °01'W), 17.14 mm, 1609–1621 m.
Type locality: 22 ° 35 'S, 39 ° 58 'W – 22 ° 32 'S, 39 ° 56 'W, Campos Basin, Southeast Brazil, Southwestern Atlantic, 1620–1623 m.
Material examined: The type material.
Description: Shell slender, biconical-fusiform, yellowish, up to 20.94 mm long. Protoconch not observed. Teleoconch whorls with a low-set shoulder forming a pagoda-like profile. Axial sculpture consists of many short fine axial riblets below the suture but not reaching the whorl shoulder, and 16–18 axial folds (on the fifth whorl). Except for the body whorl, the axial folds are angled on the whorl shoulder. Body whorl with about 28 very faint opisthocline axial ribs which extend onto the base, feebly reaching the aperture. Numerous weak and flattened spiral cords sculpture the entire surface of the whorls evenly, including the base. Suture shallow. Base elongated. Anal sinus wide and shallow. Inner lip reflected over parietal wall. Outer lip very thin. Anterior siphonal canal long and narrow. Aperture elliptical.
Etymology: Xaioca is a word in Tupy, a major language of Brazilian indigenous peoples, and means “unwrinkle”, referring to the fact that his species has strong axial ornamentation on the earlier whorls that tend to vanish as the animal grows.
Geographic distribution: Only known from Campos Basin, off Rio de Janeiro, 1609–1623 m.
Discussion: This species can be characterized by its very long anterior siphonal canal, faint spiral sculpture, axial sculpture strong and forming a shoulder on the earlier whorls and vanishing on the later whorls. Our material resembles Dall’s illustration of Gymnobela emertoni (Verrill & Smith, 1884) (Dall, 1889: pl. X, fig. 9); however, the original illustration of this species (Verrill, 1884, pl. XXXI, fig. 6) is actually quite different, as is the material illustrated by Bouchet & Warén (1980: 60, fig. 130). Our material is also similar to Theta chariessa as represented in the original illustration (Watson, 1886: PL. XX, fig. 6) and by Bouchet & Warén (1980: 60, fig. 130). However, upon examination of the figures of the type material, it is clear that both Gymnobela emertoni and Theta chariessa are larger than our material and have shorter anterior siphonal canals.