Hello Mr. Rickard,

A picture would have helped a lot as a purple colored sponge with prominent osculi can be many; in fact, upon viewing your question I found Ailochroia crassa, Ianthella basta etc which are all purple in color but not common in the Mediterranean. There is also a species in the region named Petrosia ficiformis which is somewhat purplish and fits your description . Cliona viridis is native to the Mediterranean and appears darker reddish green due to the zooxanthellae and it may be what you saw. Another Mediterranean species is Dasydiea avara with beautiful purple coloration and a good contender to be your species.

I hope one of the species is what you are looking for.

Regards,

Dr. Abhishek Mukherjee

Hello Benedict,

you can try consulting these sites

Sponges of the 'Cliona viridis complex' - a key for species identification

http://www.biologiamarina.org/category/regno-animale/poriferi/demosponge-poriferi/

http://species-identification.org/search.php?search_for=Cliona&image.x=47&image.y=17&search_mode=basic

good luck

Max

Here is a picture for clarification

Maybe Cliona schmidtii (Ridlei 1881), better with spicule preparation. :)