This is a common find on the winter strandline, and is a baseball-sized sphere comprising a mass of empty common whelk egg cases.
It’s often seen attached to rocks or stones, and colour is significant: if it’s pale yellow, there may still be some eggs inside; if it’s greyish, the young will have left. Many of the hatchlings don’t survive, gobbled up by their stronger siblings.
Main image: Sea wash ball. © Steve Trewhella/Getty