Can anyone identify this tuber-like object I found on a beach in South Wales, UK? It's about 25 cm long and looks like a deflated football. Pretty spongy, saturated with water. I was hoping it was ambergris, but that seems unlikely.
It is spongy because it is a sponge, specifically a sea sponge. There are quite a large number of them native to the waters around england. I would guess Craniella cranium based on shape and location but I am by no means an expert on sponges. Here a cross section of a cleaned sponge
and sediment laden potato sponges after a hurricane.
you can see more images of collecting these here, http://www.vims.edu/newsandevents/topstories/archives/2011/irene_blobs.php
Here is a whole website dedicated to english sea sponges, http://www.aphotomarine.com/sponge_suberites_ficus_sea_orange_sulphur.html