feather star

Common name for a type of crinoid, a marine invertebrate within the class Crinoidea and phylum Echinodermata, which also includes starfish, brittle stars, sea urchins, and sea cucumbers (fig.). In their adult form, crinoids that remain attached to the sea floor by a stalk are commonly known as sea lilies, whereas the unstalked varieties are referred to as feather stars or comatulids, and are free-swimming. These plant-like sea creatures inhabit a variety of marine environments, from shallow reefs to deeper waters, and are known for their vibrant colors and intricate arm structures. While there are about 700 species today, crinoids were more diverse in the past and contributed significantly to ancient limestone formations. Comatulids possess an internal skeleton made up of calcium carbonate plates covered by skin, along with ligaments and muscles that hold their body together. Feather stars have a mouth on their upper surface, surrounded by feathery feeding arms, called pinnules, for gathering plankton. The name Crinoidea comes from the Greek word krínon (κρίνον), meaning ‘lily’, with the suffix -oid meaning ‘-like’, from the Greek eîdos (εἶδος) i.e. ‘form’ or ‘likeness’, and reflecting their appearance. Feather stars can be found at Koh Tao (fig.), at dive sites like White Rock or Shark Island. They inhabit rocky substrates, which provide both their food and attachment points, whilst avoiding silt, as that can clog their feet. When disturbed, they swim through the water column. They often hide during the day, making nighttime the best opportunity to observe these unique creatures. White Rock, in particular, is an excellent spot for seeing feather stars during night dives. 回