Although rich in species, the fauna of Porifera in Brazil is inadequately known. During a study of the Porifera of Arraial do Cabo (Rio de Janeiro), we found eight species of the genus Clathrina (Porifera, Calcarea). C. ascandroides, C. aurea and C. brasiliensis were already described; three of them, C. conifera n. sp., C. quadriradiata n. sp. and C. tetractina n. sp., are new to science; C. aspina and C. cylindractina are being fully described for the first
time. C. ascandroides has a cormus formed by large, irregular and loosely anastomosed tubes. Water-collecting tubes are absent. Its spicules are triactines and two populations of tetractines. While the short triactines and tetractines occur outside the tubes, the large tetractines are found inside them. C. aspina has a well-delimited cormus formed by thin, regular and tightly anastomosed tubes. Water-collecting tubes are present. Spicules are triactines, tetractines and tripods. The apical actine of the tetractines is smooth. Tripods surround the cormus, delimiting it. C. aurea is a yellow Clathrina, whose cormus is formed by large, irregular and loosely anastomosed tubes. Water-collecting tubes are not present. Spicules are triactines. Actines are cylindrical, undulated and have rounded ends. C. brasiliensis is morphologically very similar to C. aspina. However, the apical actine of its tetractines has short spines. The cormi of C. conifera n. sp. and C. cylindractina are formed by large, irregular and loosely anastomosed tubes, without water-collecting tubes. Both have only triactines composing their skeletons. However, the triactines of C. conifera n. sp. have conical actines, while C. cylindractina has triactines with cylindrical to conical actines. C. quadriradiata n. sp. and C. tetractina n. sp., both have tetractines as their main spicule. However, the apical actine of their tetractines has different shapes, being conical in C. quadriradiata n. sp. and cylindrical in C. tetractina n. sp.