Spondylus aff. mimus Dall, Bartsch & Rehder, 1938

Raines, Bret & Huber, Markus, 2012, 3217, Zootaxa 3217, pp. 1-106 : 40-42

Spondylus aff. mimus Dall, Bartsch & Rehder, 1938

Figures 20 A–D

Spondylus — Luke, 1995: p. 106.

Spondylus sp. — Trego, 1997: p. 199.

Material examined. Two fragments (ca. 31 mm) (BK), including a partial valve collected by the 1957/58 Downwind Expedition ( SIO Benthic Collection, M1441) and the juvenile holotype of S. kauaiensis Dall et al., 1938 (= S. mimus Dall et al., 1938 ).

Diagnosis. Shell small, subcircular, inequivalve, inequilateral, not fragile. Exterior surface consisting of about twelve radiating ribs which are heavily spined. Spines spaced fairly far apart and concave toward the ventral margin. Between the main ribs are finer intercostal riblets with the center riblet more pronounced than the others and also spined. Internal ventral margin fluted. Hinge consisting low median teeth and deep impressed pits to accommodate the opposite valve's teeth. Color variable, creamy white to pale yellow background with irregularly spaced red to reddish orange radial rays.

Remarks. An Easter Island spondylid represented by a single glossy, yellow fragment collected by the senior author and a partial LV from the 1957/58 Downwind Expedition could not be accommodated with any of the above species.

Of the related species, Spondylus mimus from the Hawaiian Islands appears to be the closest congener. M. Severns, (pers. comm., 2010), conceded there were similarities in shape, color and spines, but noted the somewhat coarser and wider ridges between these spines, compared to S. mimus . Although he conceded there were also close similarities in the hinge, he did not accept the EI species conspecific with S. mimus .

Spondylus mimus is a very rare species and its variability is barely known. The EI material consists of fragments and juvenile material only, so at present it cannot be firmly identified. Further Hawaiian and EI material is needed for a better understanding of this/these species. For the time being, the EI fragments are treated as possibly endemic.

Dijkstra and Marshall (2008: 74) treated Spondylus asperrimus G.B. Sowerby II, 1847 , from Norfolk and Kermadec Island, and synonymized several Hawaiian species of Dall et al., 1938, notably S. mimus , S. gloriosus and S. kauaiensis .

Spondylus gloriosus however, is a characteristic Hawaiian species, well known under its former, erroneous name “ S. linguafelis ” ( Huber, 2009) . Spondylus gloriosus is also known from offshore Panamic Islands, but does not live in waters of Norfolk or Kermadec Islands ( Huber, 2009: 107, fig. 11; Huber, 2010: 216, fig. 1; Severns, 2011: 456, pl. 208, fig. 4).

Although we agree that the Hawaiian S. mimus and S. kauaiensis are conspecific, we do not concur with them being synonymized with S. asperrimus which is another characteristic species and well known from the Philippines and Australia. Neither the juvenile holotype of S. kauaiensis ( Figs. 20 E–F) nor the adult S. mimus have any resemblance to S. asperrimus . Furthermore, nothing similar to the type material of S. asperrimus , housed in Natural History Museum of London, has ever been seen from the Hawaiian Islands (see Huber, 2010: 216, figs. 2 and 3; Severns, 2011: pls. 207–209).

Habitat. Rarely found at a few locations around EI, in sand and rubble, from 50–80 m.

Distribution. At present the species is only known from Easter Island— E1.