Herouvalia rapanui, Raines & Huber, 2012

Raines, Bret & Huber, Markus, 2012, 3217, Zootaxa 3217, pp. 1-106 : 74-76

Herouvalia rapanui sp. nov.

Figures 38 A–H

Elliptotellina caelata (A. Adams, 1854) — Raines, 2002: p. 36, fig. 45.

Type Material. Holotype: LACM 3166, 1 articulated specimen, 5.9 mm. Paratypes 1–3: LACM 3167, 3 single valves, 5.4 to 11.2 mm from the type locality. Paratypes 4–11: LACM 3168, 8 single valves from La Perouse Bay , Easter Island, 27°04’26” S, 109°16’50” W, 60 m.

Paratypes 12–17: Coll. MHU, 6 single valves from Motu Iti , Easter Island, 65 m. Paratypes 18–21: Coll. BR, 1 articulated specimen and 3 single valves from the type locality. Paratypes 22–24: Coll. BR, 3 single valves from Salas y Gómez Island , 22 m.

Type Locality. Dredged at 30–50 m in fine sand, off the western coastline near Tahai , Easter Island, 27°07’20” S, 109°26’30” W .

Description. A subrectangular, finely lamellate Herouvalia species with a cancellate posterior sculpture and a short, quadrate psammobid nymph. Shell rather large for this group, reaching 11.2 mm; equivalve, subrectangular, slightly broader posteriorly, acutely rounded anteriorly; a very weak posterior flexure present; rather thin but solid; variable in color, from uniform white to red, sometimes with two reddish rays or spots; umbones small, moderately acute, weakly opisthogyrate, subcentral, nearer to the posterior end. Prodissoconch, P1 strongly pronounced, erect, round, ca. 97 µm length and 82 µm height, P2 ovate, smooth with the exception of faint growth striae, ca. 174 µm length and 155 µm height. Nepioconch deeply incised. Adult valves weakly inflated, sculpture of 25–30 fine, regular commarginal lamellae, intercalated by irregular, dense radial threads; on the narrower anterior end the sculpture is comparable to the central portion, with the commarginals slightly thinner and the radials slightly broader; on the broader posterior portion the sculpture is distinctly cancellate caused by stronger expressed radials. Microsculpture consisting of irregular pitting covers the entire surface. Hinge line solid, RV with two cardinals, the posterior stronger and knobby and two strong, elongate laterals; LV with two cardinals, the anterior knobby and two weak, distant marginal laterals. Well visible is the short “psammobid” nymph as identically figured by Keen in Moore (1969: E116 fig. 2c) for the type species H. semitexta . Pallial sinus strongly ascending, broad and rounded, deep and clearly surpassing midline. External ligament brownish on a nymph. Margins solid, posteroventrally and posteriorly weakly fluted due to the strong radial sculpture.

Comparative diagnosis. The closest species to H. rapanui are its two described congeners, the widely distributed Gafrarium (Corbis) caelatum A. Adams, 1854 , (syn. Tellina euglypta Gould, 1861 ; Tellina fabrefacta Pilsbry, 1904 , and Gari erasmia Melvill, 1898 ), from the Arabian Peninsula to Japan and Chione pulchella H. Adams, 1870 , (syn. Gari granulifera Lamy, 1938 ), from the Red Sea. Also congeneric and comparable is an undescribed species from the Marquesas Islands (coll. MHU), which has denser and finer anterior sculpture and a stronger pronounced posterior sculpture as similarly found in H. pulchella .

Most authors place these species erroneously in the genus Elliptotellina Cossmann, 1887 . However, Elliptotellina is based on a Paris Eocene fossil, which has a sculpture of only fine commarginal lirae and has a small pallial sinus, but it lacks the lateral dentition in the LV and the psammobid nymph. Instead the genus Herouvalia , also based on a Paris Eocene fossil, matches this unique group well. Herouvalia fits both in size and by having the characteristic posterior and anterior sculpture, as well as by having the ascending, broad and deep pallial sinus, an external ligament resting on a small nymph, and with lateral dentition, strong in the RV and weak marginal laterals in the LV.

In contrast to Keen in Moore (1969), Afshar (1969: 34, pl. 8) well recognized Elliptotellina and Herouvalia species as related tellinid genera. He characterised both and illustrated the Paris Basin material.

Herouvalia rapanui differs from the Red Sea H. pulchella by its shorter and higher shape and by having only commarginal anterior sculpture. The holotype of Gafrarium (Corbis) caelatum A. Adams, 1854 (BMNH 1963867) originally described from Luzon, Philippines proved to represent the same species as Gould’s later, well known T. euglypta , often illustrated from Japan. Herouvalia caelata is similar in appearance and widely distributed throughout the Indo-Pacific. However, the EI species has a much finer sculpture with many more and thinner commarginal lamellae. Its shape is subrectangular, less trigonal with a straighter hinge line and less pronounced umbones. Both species, however, share a similar broad, ascending pallial sinus, a comparable maximum size and both occur in reddish and whitish-yellow coloration.

Remarks. The Herouvalia group is widely distributed in the Indo-Pacific, from the Red Sea to Easter Island, but is not known from the Hawaiian Islands.

The London holotype of the long enigmatic 9.7 mm Gafrarium (Corbis) scitulum A. Adams, 1854 , proved to represent an unrelated Philippine lucinid, belonging to the Myrtea Turton, 1822 group, as identified by J. Taylor, (pers. comm., 2010).

Distribution. Herouvalia rapanui is commonly found from 20–100 m at many locations around Easter and Salas y Gómez Islands— E1.

Etymology. The name reflects Rapa Nui, the indigenous name for Easter Island.