[1] Petrosia ficiformis is found on the underside of rocks, on overhangs and in caves between 5 and 70 m (16 and 230 ft) deep.

Petrosia ficiformis is usually purple brown in colour due to symbiosis with photosynthetic cyanobacteria, but can be white in the absence of light.

[4] Petrosia ficiformis is specifically known to synthesize various types of Petroformynes,[5] a class of polyhydroxylated polyacetylene fatty alcohols with cytotoxic activity.

[7] Petrosia ficiformis is the main and preferred food of the nudibranch Peltodoris atromaculata, which is generally found over the sponge.

They accumulate the chemical compounds of the sponge on their digestive tract and use them as one of their defensive strategies.