Little Polychaete worms like Spirorbis borealis also filter organisms. With tentacles they catch particles outside their white spiral tube (see Wim’s article). All these strange animals form the food of others which also live under the stone: the cushion-star which uses his extractable stomach to digest his prey and the European cowrie who is the specific predator of star tunicates Botryllus. We can also find other species like the common brittle-star. This echinoderm is a passive feeder that collects small particles by putting up his arms spiked with spines. The sucker feet under the arms bring the food as far as the mouth. Under the stone live some little crabs clinging to the stone with their clawed feet; one of them is a flattened crab called the porcelain crab (Porcellana plathycheles, also see opening image) He also filters water with numerous bristles on the mouth appendix.