Maretia Gray, 1855

Holmes, Francis C., 2014, A late Miocene record of the echinoid Maretia (Echinoidea, Spatangoida) from Victoria, Australia., Memoirs of Museum Victoria 72, pp. 63-72 : 64

Genus Maretia Gray, 1855

Type species. Spatangus planulata Lamarck, 1816 , by original designation.

Other species (listed by Smith and Kroh, 2011). Maretia carinata Bolau, 1873 , M.? cordata Mortensen, 1948 , M.? tuberculata Agassiz and Clark, 1907 , M. sp. of Henderson (1975), M.? subrostrata ( Clark, 1915), and M.? aequipetala ( Gregory, 1891) .

Diagnosis. (Modified from Smith and Kroh, 2011). Test moderate in size, ovate tapering posteriorly, with or without slight anterior depression, weakly arched to depressed in profile, oral surface flat except for low posterior keel; ambitus low and moderately sharp. Apical disk slightly anterior of centre, ethmolytic with 4 gonopores, genital plate 2 projecting far to the posterior of posterior oculars. Anterior ambulacrum narrow and flush adapically, pore-pairs small, isopores simple. Other ambulacra petaloid and flush. Anterior paired petals bowed, with adapical pore-pairs in anterior column rudimentary; remainder large and semi-conjugate. Posterior petals bowed to lanceolate, converging distally. Periproct on short steeply undercut truncate face; peristome wider than long, kidney-shaped, with adoral ambulacra forming a distinct phyllode. Labral plate narrow and elongate, just contacting sternal plates adjacent to the posterior half of adjoining third ambulacral plates; paired sternal plates narrow and triangular with tuberculation confined to the posterior. Aboral tuberculation heterogenous, with scattered sunken primary tubercules on interambulacra 1-4 varying markedly in density and generally missing in interambulacrum 5. On oral surface lateral tubercles arranged in distinct rows with slightly sunken areoles and spiral parapet. Subanal fasciole shield shaped, and generally well developed.

Remarks. According to Mortensen (1951: 26), in the previous 100 or so years no less than 40 fossil species, ranging in age from Eocene to Recent, have been assigned to Maretia or Hemipatagus ; the two at times being considered synonymous. Most of the confusion in separating the two genera has been rectified by Kroh (2007) who listed species of Hemipatagus , Maretia , and presumed related spatangoids, accompanied by details of synonymy, type species and locality, and occurrence and age. Based on this information and cladistic analysis of specimens, the suggested taxonomic placement of these species was discussed in detail.

However, the seven species of Maretia listed by Smith and Kroh (2011) include four assigned to the genus with question: M.? cordata , because of it’s prominent cordate outline and distinct anterior sulcus; M.? tuberculata , considered a juvenile specimen possibly assignable to Lovenia ; M.? subrostrata, a species containing many features in common with Hemipatagus ; and M.? aequipetala , because the type material is too poorly preserved for a positive identification. Of the remaining three species, even the illustrations of M. sp. from New Zealand suggest it is most likely related to M.? cordata .