Bryozoans, commonly referred to as “moss animals” are a phylum of aquatic, invertebrate animals. They are filter feeders that sieve food particles from water using a crown of tentacles lines with cilia. Most bryozoan live in tropical waters although some live in oceanic trenches and polar waters. Most of the 4,000 known species are colonial in habit. All of the freshwater spies are simultaneous hermaphrodites while many marine species function first as males and then as females. All species emit sperm into the water with some also releasing ova into the water. Predators of marine bryozoan are sea slugs, sea urchins, crustaceans, mites, and starfish. Freshwater bryozoans are preyed upon by snails, insects and fish. Mineralized skeletons of bryozoans first appeared in rocks of the Early Ordovician, making it the last major phylum to appear in the fossil record.