The Sea Cucumber: Wonderful Echinoderm for a Reef Tank

Sea cucumbers are members of the echinoderm family and class holothuroidae. They are found entirely in the marine environment from the depths to the shallow sandy regions of lagoons and tidal areas. For the most part these echinoderms are scavengers that consistently comb the benthic areas of reefs and sandy, muddy biotopes in search of algae, microscopic foods stuff and plankton plus decayed matter and detritus.

There are over 1000 species of holothurids, that range in size from a half inch or so to over eight feet in length and weigh a mere ounce to a whopping 11 pounds (Stichopus Sea Cucumber).

These echinoderms, relatives of the Sea Star and Sea Urchin, are mainly leathery to the feel, with bumps or protrusions called, papillae and have an elongated body. Most of these also have an endoskeleton which lies just below their skin. An endoskeleton is the internal support system for the Sea cucumber.

Coloration associated with the sea cucumber can be very drab with cream, brown, black and white being the major colors, with others showing vibrant yellows, pinks and greens. Because these echinoderms are bottom dwelling animals that spend a great deal of time on the substrate or buried below it, they have to be able to blend into their surroundings to help them ward off predators.

Cucumbers have tube feet, similar to urchins and sea stars. They do not have a brain but have numerous sensory nerve endings that are highly sensitive. These nerve endings are located in the epidermis, with the bulk of these endings around the mouth and anus area. Breathing is achieved through a specialized respiratory tree located in the coelom (body cavity). This unique paired organ allows water to be purged rhythmically through muscular contractions, similar to propulsion by an octopus. This also enable the animal to discharge ammonia as a bio product of gas exchange.

They have a couple other forms of protection and defenses however. Many of these cucumbers are able to release sticky strands of filament that is released from the cucumbers anus. Others are able to basically release some of their internal organs through a process known as evisceration. The guts (cuverian tubules) are toxic to fish and also occasionally harmful to humans. The cuverian tubules are also released from the anus as another way of warding off would be predators. These guts and other internal organs are able to be replenished within a matter of weeks which is an amazing fact.

The toxicity of various sea cucumbers is a challenging question. Most are non-venomous to humans, though if not prepared or eaten properly, serious issues can result. For the most part the problem arises to divers and aquarists in the collection and handling of these echinoderms. In the event that a cucumber does eviscerate its inside and you get this sticky substance on your hands if not properly removed, and you make contact with the mucus membrane area of your eye, often times you can contact "pink eye" conjunctivitis or "keratitis" which is an inflammation and infection of the cornea and is associated with pain, swelling, redness, blurred vision and irritation. Professional medical attention is advised with the contact of this ailment.

If you plan on purchasing one of these diverse echinoderms, care must be addressed to not irritate, stress or injure this animal, through the act of yourself or other tank mates. If the cucumber dies or at the very least eviscerates its insides (entrails) into your water, you run the risk of poisoning (holothurin) the animals in your tank. Prompt water change and carbon addition will help to dilute this problem from getting further out of hand. These animals can be of utmost importance to a reef tank due to its feeding ability and cleaning/aeration of the benthic area of your tank.

The main key is to acclimate slowly and correctly and to maintain proper husbandry and water parameter guidelines. I have kept one of these cucumbers in my 125gallon reef tank for about a year now, and the advantages and benefits of maintaining it in my tank far outweighs the cons in this case. None of my fish or other invertebrates have attacked or picked on my cucumber...it is like it doesn't exist-sort of an out of site out of mind theory! My cucumber is only evident at night after my lights go off, then it is consistently foraging and combing the substrate for food.