Pleurotomella ybessa, Figueira, Raquel Medeiros Andrade & Absalão, Ricardo Silva, 2012

Figueira, Raquel Medeiros Andrade & Absalão, Ricardo Silva, 2012, Deep-water Raphitomidae (Mollusca, Gastropoda, Conoidea) from the Campos Basin, southeast Brazil, Zootaxa 3527, pp. 1-27 : 24-26

Pleurotomella ybessa n. sp.

( Fig. 51–55 )

Type material: Holotype MNRJ 30285 [1] OP I # 7 (22° 45'S, 40° 19'W - 22° 44'S, 40° 16'W), 12.26 mm, 1118–1130m. Paratype IBUFRJ 19191 [2] OP I # 84 (22° 26' 27"S, 39° 58' 51"W), 2.66 mm and 6.06 mm, 1050m. Paratype MZSP 108230 [3] OP I # 60 (21° 52' 50"S, 39° 51' 42"W), 1.68 mm, 1.98 mm and 6.3 mm, 1050 m. Paratype MCZ 374809 [1] OP I # 75 (22° 31' 28"S, 40° 03' 50"W), 5.88 mm, 1050 m. Paratype MCZ 374810 [2] OP I # 58 (21° 57' 26"S, 39° 40' 33"W), 2.12 mm and 3.44 mm, 1950 m. Paratype MNHN [2] OP II # 63 (21° 52' 43"S, 39° 40' 41"W), 2.52 mm and 3.56 mm, 1941m. Paratype USNM 1187764 [2] OP I # 61 (21° 52' 51"S, 39° 48' 11"W), 2.46 mm and 4.56 mm, 1350m.

Type locality: 22° 45'S, 40° 19'W – 22° 44'S, 40° 16'W, Campos Basin, Southeast Brazil, Southwestern Atlantic, 1118–1130 m.

Material examined: Type material and 19182 [5] OP I # 45; 19183 [2] OP I # 47; 19184 [1] OP I # 50A; 19185 [1] OP I # 57; 19186 [2] OP I # 58; 19187 [1] OP I # 60; 19188 [1] OP I # 61; 19189 [1] OP I # 75; 19190 [1] OP I # 83; 19191 [2] OP I # 84; 19192 [1] OP II # 48; 19193 [1] OP II # 50A; 19194 [3] OP II # 63; 19195 [2] OP II # 80; 19196 [1] OP II # 84; 19197 [1] OP II # 86; 16392 [1] OP I # 7; 19198 [1] B # 32.

Description: Shell biconical, white, up to 12.26 mm long. Protoconch with about 3.5 whorls. Protoconch 1 with spiral rows of tiny crosses. Protoconch 2 with diagonal cancellation on the lower 2/3 of the whorls and axial riblets crossed by very fine and faint spiral threads on the upper third. Clear-cut proto-teleoconch boundary. Teleoconch whorls middle angled, with a slightly concave region between the suture and the shoulder. Axial sculpture consists of 12–14 well spaced and thick ribs (on the third whorl) below the whorl shoulder and several very weak arched axial threads above it. Spiral sculpture consists of about 3 spiral cords below the whorl shoulder, and a thick subsutural ribbon ornamented by short prosocline axial ribs. Shell surface covered by spirally organized granules. Suture well marked. Base elongated and with an inflection, sculptured with about 8 spiral cords. Anal sinus wide and deep. Inner lip reflected over parietal wall. Outer lip thin. Anterior siphonal canal relatively long and narrow. Aperture elliptical.

Etymology: Ybessa is derived from ybesse which is a word in Tupy, a major language of Brazilian indigenous peoples, and means “not too dense”, referring to the fact that this species has few short axial ribs below the suture.

Geographic distribution: Only known from Campos Basin, off Rio de Janeiro, 900–1968 m

Discussion: This species is diagnosed by the rather thick subsutural ribbon crossed by short axial ribs. Also the axial threads below the suture are quite faint when compared with those of the other Pleurotomella species. The closest species to this one is P. bureaui (fig. 49), but P. ybessa can be distinguished by its larger profile, the thick subsutural ribbon ornamented with short prosocline axial ribs and the fainter subsutural axial threads.

Figures

FIGURES 47 – 55. 47, 48 — Pleurotomella cf. anceyi Dautzenberg & Fischer, 1897, IBUFRJ 18984; 47 — 6.90 mm, whole shell; 48 — protoconch. Figures 49, 50 — Pleurotomella bureaui Dautzenberg & Fischer, 1897, IBUFRJ 19201; 49 — 4.30 mm, whole shell; 50 — protoconch. Figures 51, 52, 53, 54, 55 — Pleurotomella ybessa n. sp.; 51 — Holotype MNRJ 30288; 12.26 mm, whole shell; 52, 54, 55 — Paratype IBUFRJ 19191, 52 — 6.06 mm, whole shell; 54 — detail of shell surface; 55 — protoconch; 53 — Paratype MCZ 374809; 5.88 mm, whole shell. Scale bars: 47, 49, 52 and 53 = 750 μm; 48, 50 and 55 = 250 μm; 51 = 2 mm; 54 = 25 μm.