Newly discovered coralline algae in Southeast Brazil: Tectolithon fluminense gen. et sp. nov. and Crustaphytum atlanticum sp. nov. (Hapalidiales, Rhodophyta)

Two new Melobesioideae, Tectolithon fluminense gen. et sp. nov. and Crustaphytum atlanticum sp. nov., were described based on specimens collected at depths from 2 to 30 m in a tropical to subtropical transitional region of Southeast Brazil. Analyses of the plastid-encoded markers psbA and rbcL demonstrated that these taxonomic novelties belong to the clade formed by the typically subarctic/arctic Clathromorphum complex. Tectolithon fluminense has tetra/bisporangial and carposporangial conceptacles that typically become buried in the thallus because of an enveloping process caused by the development of a vegetative rim that grows from the margins of the conceptacle. The rim then fuses and creates a vegetative cover. The development of this vegetative cover is described in detail and its possible convergent evolution in other taxa is discussed. Crustaphytum atlanticum differed morpho-anatomically from the generitype, C. pacificum (the only other known species in this genus), by thallus thickness, maximum number of epithallial cell layers, relative size of subepithallial initials and tetra/bisporangial conceptacle chamber dimensions. The observation of specimens from Tectolithon and Crustaphytum with subepithallial initials that are both longer and shorter than their immediate inward derivatives indicates that this morpho-anatomical character should be used with caution for generic delimitation in the Melobesioideae.