Systema Porifera:A Guide to the Classification of Sponges, Edited by John N.A. Hooper and Rob W.M. Van Soest © Kluwer Academic/Plenum Publishers, New York, 2002 DEFINITION, DIAGNOSIS, SCOPE Synonymy Petrosiidae Van Soest, 1980: 66. Definition (from Van Soest, 1980) Haplosclerida with an ectosomal skeleton consisting of an isotropic reticulation of single spicules or spicule tracts and a choanosomal skeleton verging towards an isotropic reticulation of spicule tracts, in which primary and secondary tracts are indistinct. Diagnosis (emended from Van Soest, 1980; Hooper & Wiedenmayer, 1994) Massive, volcano or vase-shaped, bulbous and less com- monly, encrusting-branching sponges. Sponge texture characteris- tically stony and brittle due the high silica content of the mineral skeleton, about 58% relative to spongin content of the skeleton (Desqueyroux-Faúndez, 1987). Surface smooth, covered by a smooth, strong crust or variably hispid. Specialised ectosomal skeleton consisting of an isotropic tangential reticulation of free spicules or spicule tracts, forming the mineral crust. Choanosomal skeleton is a more-or-less regular isotropic network of multispicu- lar tracts where primary and secondary fibres are indistinct. Spongin not visible, spicules bound together with the minimal amount of spongin. Multispicular tracts are regularly distributed to form, rounded meshes parallel to the surface, that can be ill defined or masked by the abundant free spicules. Megascleres: oxeas to strongylotes. Microscleres if present, smaller oxeas. In one sub- genus (Strongylophora), smaller, sausage-shaped strongyles exist. Spicule types and size classes are very variable within different genera, ranging from only one type of spicule in only one size class, smaller than 200 m long (Neopetrosia) or larger than 200 m long (Xestospongia), up to two types of spicules with five size classes (Strongylophora). Spicule morphologies and sizes are considered important taxonomic characters among different genera, since they are fixed and stable for each genus (Table 1). Oviparous reproduction is known for only one genus (Xestospongia), which is gonochoric and has synchronous spawning (e.g., Fromont, 1988), but larvae are unknown (Bergquist, 1980a). Scope Nine nominal genera and hundreds of species are known worldwide, of which only four genera and two subgenera are con- sidered valid here: Acanthostrongylophora, Neopetrosia, Petrosia (Petrosia), Petrosia (Strongylophora) and Xestospongia. Densa and Quepanetsal are included in synonymy with Xestospongia, with question, as are Tedaniella and Chalinorhaphis included in Petrosia. Species are distributed in shallow and deeper tropical, warm-temperate to cold waters, with depth range 4–280 m. History and biology The family was erected by Van Soest, 1980 to include Haplosclerida with an ectosomal skeleton consisting of an isotropic reticulation of single spicules or spicules tracts and a choanosomal skeleton verging towards an isotropic reticulation of spicule tracts, in which primary and secondary tracts are indistinct. Van Soest (1980) split the genera previously grouped in Nepheliospongiidae Clarke, 1900 by Wiedenmayer (1977a) into two new families: Petrosiidae and Oceanapiidae. Van Soest (1980) sug- gested that it was uncertain whether Recent genera such as Petrosia and Xestospongia were closely allied with the fossil genus Nepheliospongia, as implicitly indicated by their inclusion in a single family Nepheliospongiidae. Wiedenmayer (1977a) defined Nepheliospongiidae principally by the strong development of megascleres in relation to spongin, hence with hard or friable consis- tency, the presence of a skeletal accretive structure with ascending and radially diverging skeletal tracts, and the tendency to have a tan- gential ectosomal network or peripheral crust. At the same time, Wiedenmayer (1977a) associated a fossil group Heliospongiidae Finks, 1960 with Nepheliospongiidae, which in his opinion shared the same characters of spiculation, skeletal architecture and aquifer- ous system, with living Nepheliospongiidae. Wiedenmayer (1977a) included in this family: Petrosia, Xestospongia, Cribrochalina, Hemigellius, Vagocia, Calyx, Rhizochalina, Oceanapia, Biminia and Siphonodictyon. Bergquist & Warne (1980: 35) accepted, but modified, the diagnosis of Nepheliospongiidae Clarke given by Wiedenmayer (1977a). They included only two genera having a mineral skeleton predominant over the soft tissues, and a greater development of a spiculose ectosomal layer. In one genus (Petrosia) this is represented 906 Family Petrosiidae Van Soest, 1980 R. Desqueyroux-Faúndez 1 & C. Valentine 2 1 Muséum d’histoire naturelle, P.O. Box 6434, CH-1211 Geneva 6. Switzerland. (ruth.faundez@mhn.ville-ge.ch). 2 The Natural History Museum. Cromwell Road, London, SW7 5BD, UK. (c.valentine@nhm.ac.uk) Petrosiidae Van Soest (Demospongiae, Haplosclerida) contains four valid genera and two subgenera. Species are widely distributed in shallow and deeper warm-temperate to cold waters. Genera share a reticulated tangential ectosomal layer of spicules, or surface crust and are differentiated by their choanosomal skeletal structure, varying from isotropic-confused to isotropic-lamellate, and their types and size classes of spicules. Keywords: Porifera; Demospongiae; Haplosclerida; Petrosiidae; Acanthostrongylophora; Neopetrosia; Petrosia (Petrosia); Petrosia (Strongylophora); Xestospongia.