Sperosoma Koehler, 1897

Type species: Sperosoma grimaldii Koehler, 1897, by original designation.

Diagnosis. Sperosomatinae with primary ambulacral plates of the oral side divided into two parts separated by the secondary plates, the inner part non-poriferous (emended from Fell 1966).

Remarks. Of the eleven known species of Sperosoma (Table 1), the descriptions of six were based on a single specimen, and of the remaining five only one, S. grimaldii, was known from more than the type material at the time of the most recent review of the genus (Mortensen 1935). Unlike many other echinothurioid genera, the pedicellariae of Sperosoma are relatively similar between species and usually of secondary diagnostic value, with reliance instead mainly on differences in coronal plate architecture, particularly in the aboral ambulacra. A more recent examination of the aboral plating of Sperosoma species (Mooi et al. 2004) has shown that some of these apparent differences were based on post-mortem fractures misinterpreted as plate boundaries. A full review of the genus is needed to confirm the validity of each species, but sufficient material is still lacking. The two Australasian species reported below do not appear substantially different from descriptions of existing species, and therefore further confusion is avoided by not establishing any new species here.