Crinoids are amazing, colorful, flower-shaped animals living in the deep seas all over the world. Their name is of Greek origin – it means lily-shaped and indeed, these special creatures have long, thin, colorful arms that make them look like lilies. There are around 600 crinoid species known to scientists today, even though they used to be much more abundant before the Permian period (298.9 – 252.17 million years ago) when they underwent mass extinction.
The body of these flower-like animals is comprised of three distinct sections. They have a stem, the part made up by small ossicles, and ligaments that they use for attaching themselves to the substrate; they also feature a calyx, a cup-like section that comprises the animal’s reproductive and digestive tract, including the mouth and the anus as well, and the long, symmetrical feeding arms that are also made up of tiny ossicles.
Most crinoid species are free swimming, their stalk having lost its ancestral function of fastening the animal to the substrate, with only a few species dwelling the deep waters using their stems as an anchoring device.
These beautiful, flower-like creatures are diverse in terms of size. The largest individuals can grow to 3 ft. in diameter and can have up to 200 arms. They also come in many different colors, orange and white being just as common as yellow, red and green.
Most crinoid species are filter-feeders, availing themselves to small food particles, tiny crustaceans, planktons and algae floating in the water with the help of their long, articulate and powerful arms. The tube feet of the animal is covered in a kind of sticky mucus that attracts and traps the particles that float around freely in the water and the mucus is then directed towards the mouth. They are nocturnal animals, spending most of the day with their long arms wrapped around their stem to form a ball and opening to feed only during the night.
Crinoid species proliferate by means of external fertilization of the eggs released by the female with the sperm released by the male. The fertilized eggs swim freely until hatching into tiny, barrel-shaped larvae. The larvae then settle on the substrate and attach themselves to the sea floor with their special organs, then the metamorphosis into adult individuals begins. Though many crinoid species are free-swimming, even these species start their life as larvae attached to the substrate. They break free only later, when they are fully developed.
These flower-like animals have very few parts that are edible for predators, and some of them protect themselves by making the mucus that covers their body toxic, so they are very rarely attacked by fish and other animals of the sea. There are a lot of other species of animals such as small shrimps and fish that seek shelter among the long arms of the crinoids; Merlet’s scorpionfish even protects itself by developing long fingers that look similar to crinoid arms.