A new four-plated chthamalid genus, Tetrachthamalus, is described. The arrangement of wall plates is identical to that seen in the Lower Miocene chthamalid, Tessarelasma, but the two are not closely related. While Tessarelasma has been derived from the Hexelasma-Pachylasma group, Tetrachthamalus is derivable from the Chthamalus stellatus group. An analysis of four-platedness in the Balanomorpha suggests that a four-plated organization plan is in part an adaptation to an intertidal existence.
Two populations of Tetrachthamalus are known; one from the upper end of the Red Sea, the other from the islands of the Seychelles-Mauritius Ridge in the Indian Ocean. No significant differences between the two were found, and they have been assigned to the same species; Tetrachthamalus oblitteratus gen. et sp. n. The disjunct and restricted distribution suggests T. oblitteratus is not presently competitive with six-plated chthamalids occupying the same habitat in the intervening areas–that is, the species is presumed to be a biological relict that at one time enjoyed a wider distribution than it does today.