Porolithon improcerum (porolithoideae, corallinaceae) and mesophyllum macroblastum (melobesioideae, hapalidiaceae): New records of crustose coralline red algae for the Southwest Atlantic Ocean

Here we describe in detail two crustose coralline red algal (CCA) species newly reported for the southern Atlantic: Porolithon improcerum and Mesophyllum macroblastum. Porolithon improcerum was recorded on the remote oceanic island of Martim Vaz (ca. 1,200 km off the Brazilian Coast) and M. macroblastum on the Cagarras Archipelago (ca. 5 km off the coast of Rio de Janeiro city). Within the genus Porolithon, P. improcerum is characterized by thin vegetative thallus composed mostly of two cell layers and thalli forming several applanate branches overgrowing one another. Within the genus Mesophyllum, M. macroblastum is characterized by bearing volcano-like multiporate tetrasporangial conceptacles with a raised rim and sunken central pore plate in addition to pore canals of conceptacles being lined by cells that are similar in size and shape to other roof cells. While, P. improcerum has previously been reported for the northern Atlantic Ocean, this study represents the first report of M. macroblastum for the Atlantic Ocean