The nudibranch is often called a seaslug; however, that name implies it is ugly. Many nudibranchs are considered to be among the most beautiful of marine animals. There are hundreds of different species. They range in size from less than 1/2 inch to two feet long and come in many shapes and bright colors. Their bodies are often covered in frills or fronds to help conceal them from predators. They are shell-less mollusks and can be distinguished by stalked sensory organs at the top of their head and by fingerlike, club-shaped respiratory structures on their backs.
Nudibranchs are carnivores. They eat sponges, coral, sea fans, jelly fish and anemones. They have few predators because they are poisonous and also taste bad!
Those nudibranchs that eat anemones or jelly fish are not affected by the stinging cells. They have developed an ability where they incorporate the stinging cells into their own bodies to defend themselves against being eaten.