Original: This serves either as a warning , when they are poisonous or contain stinging cells , or to camouflage them on the brightly-colored hydroids , sponges and seaweeds on which many of the species are found .
Simplified: Sea slugs are often flamboyantly coloured , either as a warning if they are poisonous or to camouflage them on the corals and seaweeds on which many of the species are found .