Ceriantharia

The tube-dwelling anemones ("Ceriantharia") are a subclass of the Anthozoa. They resemble sea anemones. Sea anemones have a base plate, tube-dwelling anemones do not. 
Most tube-dwelling anemones reproduce sexually. About 100 species have been described; most live in a depth of less than . Unlike sea anemones, tube-dwelling anemones live in soft sediments. The name "tube-dwelling anemone" comes from the fact that these animals build a tube out of the sandy sediments. In the case of danger, they retract into the tube.