Rictaxis sanguinea, Valdés, 2008

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 596

Rictaxis sanguinea n. sp.

Figs 2E-H, 5

TYPE MATERIAL. — Holotype MNHN 20270 and 18 paratypes MNHN 20271, 1 paratype LACM 2977 .

TYPE LOCALITY . — Tonga, southwest of Tongatapu, 21°16’S, 175°18’W, 427-436 m [ BORDAU 2 : stn DW 1543 ] .

MATERIAL EXAMINED. — Norfolk Ridge. SMIB 8 : stn DW 146 - Tonga. BORDAU 2 : stn DW 1543 , SW of Tongatapu, 21°16’S, 147, Banc Eponge, Mont B, 24°55’S, 168°22’E, 508-532 m, 18 dd, 175°18’W, 427-436 m, 1 lv, holotype ( MNHN 20270 ; Figs paratypes ( MNHN 20271 ; Fig. 2H); stn DW 169 , Banc Stylaster, 2E-G) .

23°37’S, 167°42’E, 447-450 m, 1 dd, paratype ( LACM 2977).

DISTRIBUTION. — Known only from Tonga and Norfolk Ridge (Fig. 5), in 436-508 m, live in 427-436 m.

DESCRIPTION. — Shell morphology. Length 2.5 mm, width 1.3 mm (holotype). Shell solid, oval, with convex sides (Fig. 2E). Body whorl very large, about 5/6 of the shell length. Spire short, conical, with 2 compressed whorls. Suture slightly channeled. Protoconch globose, about 1.2 whorls and approximately 400 Μm in diameter (Fig. 2F). Umbilicus closed. Aperture wide and elongate, wider anteriorly, about 4/5 of the body whorl length. Columellar margin thickened, slightly oblique, with a small, simple fold. Sculpture of a number of punctuated spiral grooves (Fig. 2G). The punctuations are conspicuous, oval, and situated next to each other within each groove. The grooves separated by gaps several times wider than the grooves in the middle of the spire, and about as wide as the grooves near the edges of the spire. Colour uniformly cream with a dark red, thin band at about 1/3 of the spire height from the top of the spire.

Anatomy. The radular formula is 78 x 11.0. 11 in the holotype. The inner radular teeth are hamate, with a short, rounded base and an elongate and curved cusp with several sharp denticles (Fig. 2H). The outermost lateral teeth have a much more elongate base with a long cusp lacking denticles. The teeth increase in size towards the outer edge of the radula.

REMARKS. — This species is assigned to Rictaxis based on the presence of a radula with short and multidenticulate inner lateral teeth and very elongate and smooth outer lateral teeth. The other two known species of Rictaxis , R. punctocaelatus and R. punctostriatus , both redescribed by Marcus (1972), have similar radular morphology but with a smaller number of lateral teeth. Rictaxis punctocaelatus also has darker spiral bands on the shell, but the shell is much more elongated.

Rictaxis sanguinea is externally distinguishable from other Indo-Pacific Acteonidae by having a dark red band on the shell.

ETYMOLOGY. — From the Latin sanguineus (bloody), in reference to the dark reddish band on the shell of this species.