Systematic revision of the genus Petromica Topsent (Demospongiae : Halichondrida), with a new species from the southwestern Atlantic

The status, scope and classification of the sublithistid demosponge genus P etromica Topsent are revised through morphological analysis of museum speci mens of all seven species (including proposed synonyms and varieties), two of which were collected and observed in situ along the Brazilian coast (P. ciocalyptoides (Van Soest & Zea) and P. citrina sp. n.). The synonymy of Pe tromica and Monanthus Kirkpatrick with priority to the former is justified due to the consistent presence of monocrepid rhizoclone desmas and oxeas in an halichondroid arrangement, and to the lack of co-variance in other morp hological characters among the species studied (presence and shape of papil lae, surface texture, ectosomal skeleton and desma shape). The proposed syn onymy of P. grimaldii Topsent and P. massalis Dendy is refuted due to diffe rences in habit and spicule shape between the two species. Three forms desc ribed as varieties of Monanthus plumosus Kirkpatrick are raised to species level: P. plumosa (Kirkpatrick), P. tubulata (Kirkpatrick) and P. digitata (Burton). Phylogenetic analysis indicates that two possibly monophyletic cl ades may be recognized within Petromica, although with low bootstrap suppor t (35-59%): (P. ciocalyptoides, P. citrina) and (P. grimaldii, P. massalis) (P. plumosa) (P. tubulata) (P. digitata). The classification of Petromica within the Halichondriidae (order Halichondrida) is supported by the confus ed reticulation of long oxeote spicules with ascending spicule tracts, pres ent in all species of the genus.