Invertebrates: Crinoids, or Feathers of the Sea

I am sure that many of you, marine aquarium enthusiasts out there, have at least one species of sea star residing in your aquarium. I can also assure those of you that think they do not possess a sea star in their aquariums, that you do, in fact have at least one species of these cryptic and beneficial invertebrates residing within the confines of your aquarium. Sea stars make wonderful additions to the benthic areas of an aquarium. If, sea stars tickle your fancy and you are always on the look out in search of another piece to the puzzle, in terms of adding diversity and echinoderms in your aquariums arsenal is concerned...search no further! The crinoid or comatulid is a perfect match.

The crinoids or as some refer to as feather stars or sea lilies are one of the oldest creatures with fossilized records dating back to the Ordovician Period, some 430 million years ago. Now, don't think that these stars as a spin off of the "Munsters" television show with grandpa being hundreds of years old. It is a tribute to their ability however, to be able to evolve and coexist throughout time, as the fate of many other living animals has not been as kind with the species becoming extinct. Populating our earth for some 440 million years or so, their are over 550 species of comatulid worldwide.

Crinoids are echinoderms meaning spiny skin. They are categorized with other Sea Stars and Sea Urchins. Illustrated by numerous feathery appendages or arms that, often times, are very beautifully colored, these animals are truly a sight to be seen. Each arm contains numerous tube feet which they use to adhere to their surroundings as well as provide mobilization. Their arms also contain microscopic cilia on their underside which is used primarily as a feeding mechanism. The cilia flutter in wards causing a stream of water that basically sucks in the tiny food particles towards the crinoids mouth in the center of its body.

These echinoderms are considered suspension feeders in that they feed on detritus and other suspended matter for the most part that remains suspended in the pelagic areas of oceans or aquariums. Depending on the species, some crinoids may have up to 200 arms and the size of each star ranges from small to an excess of 14 inches or so. The most distinguishing characteristic between that of a sea star and a crinoid besides the number of arms is that the mouth of a crinoid is pointed up wards.

As mentioned above the coloration of many of these feather stars is astonishing! Sometimes contrasting in color between the feathery plumes and the crinoids arms, colors such as red, yellow, blue and orange can be frequently seen. When disturbed or scared, the crinoid will shrivel up and retract its feathery appendages, but once the echinoderm extends its arms into the current it remains a spectacle to be seen. Divers often are astonished and amazed by the delicate beauty and coloration portrayed by these unique animals.

When one is drawn to the beauty of these animals, many times we neglect to see beyond the star and witness the commensal creatures that rely on the stars for food and shelter. Tiny shrimp, cling fish and squat lobsters are just some of these commensal animals that are heavily reliant upon crinoids for their existence. Similar to that of clown fish or anemone shrimp that is so reliant upon its host anemone, this is yet just another spectacle that should be witnessed.

Crinoids are not as common to the marine aquarium hobby, but they are encountered periodically. The availability on line as opposed to through a local pet shop is probably the way to go. As with any echinoderm, care should be taken when selecting a crinoid as well as the acclimation process from one tank to the next. When selecting the right crinoid for your tank, care should be given in selecting the right place for the placement of the crinoid in your tank. Moderate water flow area is essential as again these beauties are suspension feeders reliant upon suspended matter that is scooped up and trapped by the cilia of these animals. Being that these are very delicate and sessile invertebrates, it is essential not to purchase one of these with more boisterous fish or other invertebrates that may prey on or stress out these stars.

Being that these animals are so diverse and can ofter such a splash of color to an aquarium, it would be quite a thrill to incorporate one of these animals into your aquarium. The key is to find a healthy specimen initially at your retailer that has shown its full expansion of its arms. If they are always shown retreating to a retracted pose, chances are it is not healthy or some other underlying factor is provoking this behavior which if not rectified, will result in the death of this gorgeous animal.

I would at least read up on these animals and see if they would be a exact fit into your reef aquarium to offer you years of enjoyment and that something extra to set your aquarium apart.

http://www.fossils-facts-and-finds.com/crinoids.html

http://en.wikipedia.org/wiki/Crinoids