Petrosia ficiformis, commonly known as the stony sponge, is a species of petrosiid sea sponge in the order Haplosclerida.
Taxonomy Petrosia ficiformis was first described by J.L.M. Poiret as Spongia ficiformers. Its name comes from the Greek: "pétra" - πέτρα - rock, "physis" - φύση - nature, "fórma" - φόρμα - shape, meaning "naturally-shaped rock". It is classified under the subgenus Petrosia of the genus Petrosia.
Distribution Petrosia ficiformis occurs in the Mediterranean Sea and in the adjacent eastern Atlantic Ocean. It is found among rocks and in caves and rock crevasses, typically deeper than .
Characteristics Petrosia ficiformis is usually purple brown in colour due to symbiosis with photosynthetic cyanobacteria, but can be white in the absence of light. It has a compact, hard texture, with spherical oscula irregularly spread over the surface.
Chemistry Petrosia ficiformis biosynthesizes various acetylene derivatives. A characteristic example of this is petrosynol,Krebs, H. C. en Progress in the Chemistry of Organic Natural Products; Volume 49, Herz, W., Grisebach, H., Kirby, G. W., Tamm, C. Ed. Springer-Verlag: Wien-New York, 1986; pg 151-319. a polyacetylene of 30 atoms, which was isolated in 1987 from this animal. It likely helps to protect the sponge from bacterial and fungal infections.Meglitsch, P.A.; Schram, F.R. Invertebrate Zoology; 3 Ed, Oxford University Press: New York; 1991; page 623.
Petrosia ficiformis is specifically known to synthesize various types of petroformynes, a class of polyhydroxylated polyacetylene fatty alcohols with cytotoxic activity. The skeleton of these toxins is formed by a hydrocarbon chain of 46 to 47 carbon atoms.Férnandez-Trillo, 2004, PhD Dissertation, Universidad de Santiago de Compostela, Síntesis de Poliacetilenos de Origen Marino: Síntesis de Callyberinas A-C y (−)-Siphonodiol.
Predators Petrosia ficiformis is predated by the nudibranch Peltodoris atromaculata. This nudibranch is a specialist on Petrosia, along with the chemically similar Haliclona fulva. There is no evidence that the nudibranch uses the chemical compounds of these sponges in their own defense, as is known for many other nudibranchs.
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