Underwater Plant? No, It's Crinoid!

Crinoid is an aquatic animal that lives at the seabed, anywhere in the world. Although it is an animal, the appearance looks much more like plant.

Crinoid term comes from two Greek words; krinon (lily), and eidos (form). So, if we translate the word Crinoid, it means "form of lily". It is named so, because its appearance is similar to lily, but it's not a lily. It belongs to Echinodermata phyllum, which is included in Animalia kingdom.

Another characteristics of Crinoids beside its similar shape to lily, are that Crinoids live under water, along with other Echinodermata animals, such as starfish and sea urchin. They live in shallow water and in depths as great as 6,000 metres. They move passively, and they have their own stems used to attach their body to the substrate. Some of them live as a juveniles, and by the time they reach adult stage, they become a free-swimming animal. In top of their body, Crinoids have mouth on the surface that is surrounded by feeding arms. Their anus are located next to the mouth. Echinodermata's common characteristic is that it has fivefold symmetry, but most Crinoids have more than five arms.

Crinoids eat the small food particles from the sea water and they filter it with their arm. It has sticky part, so the food particles will stick into the arms, and they will pass through the ambulacral gap that has cilia inside it. The food particles will be brought into the mouth, and after it is digested by the digestive tract located at calyx, the food particles will be excreted by anus. The interesting fact about Crinoids is that they are used to identify the population of plankton in that area. If Crinoids have longer arms, the area has small population of plankton, and vice-versa.

Reproduction of Crinoids can happen sexually and asexually. The asexual reproduction is done by regenerating its body part, and the sexual reproduction is done by external fertilization. They are dioecious, which is the opposite of hermaphrodite. Its body cavity is tight and narrow, and it has gonad that is located in the pinnules. Some Crinoids hold their eggs inside the pinnules and let them hatch, but some release the eggs to the water and let them hatch outside the pinnules. After the egg hatches, it grows into young larvae that doesn't have mouth. After few days, the larvae will escape from its pinnule, and it will attach to the seabed and it will grow its calyx and arms. If it loses the calyx, it will grow another calyx because of its high regeneration.

There are many other informations related to Crinoids. They are nocturnal animals, and they live colonially. Some Crinoids can detach their stem and walk over the seabed, and even swimming in the sea, and they can attach their stem to their substrates. Researchers suspect that Crinoids run away from the hungry predators. They usually have vibrant colours in the tropical sea, and they have pale colours when in the cold sea, for an unknown reason. See the difference below. (The left one is in the tropical sea, and the right one is located at northern part of sea.)

Source:
1. Wikipedia (http://en.wikipedia.org/wiki/Crinoid)
2. blogpembelajaranbiologi.blogspot.com (http://blogpembelajaranbiologi.blogspot.com/2013/04/crinoidea.html)