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Diadema setosum, also known commonly as the Hatpin Urchin or Black Longspine Urchin, is an excellent addition to a mature reef tank.
Diadema setosum, known commonly as the Hatpin Urchin or the Black Longspine Urchin is a relatively common aquarium invertebrate. This is an Indo-Pacific urchin from the genus Diadema, which also includes D. antillarum (Tropical West Atlantic). D. paucispinum (East and South Pacific) and D. savignyi (Indo-Pacific from Africa to the South Pacific). D. setosum can be found from the Red Sea to Japan and throughout the South Pacific. It is readily distinguishable from other members of the genus by way of the red ring around its anus. As with all urchins, the animal possesses a hard skeleton known as a test (derived from the Latin "testa" which translated to shell or tile). The urchin is covered by this species’ namesake spines. Urchins have a downward facing, aboral mouth or, as Aristotle put it, an urchin “has what we may call its head and mouth down below, and a place for the issue of the residuum up above.” In addition to the upward-facing anus which excretes solid waste, urchins expel waste (ammonia) through their gills. Many urchins are quite mobile, as any aquarist who keeps species from the genus Diadema knows. Urchins move by way of a water vascular system with tube-like feet, and they are surprisingly quick (relatively speaking, of course). Members of the phylum Echinodermata, they are related to starfish and move in much the same way. The phylum name is derived from the Greek, and translates into hedgehog. D. setosum will grow to about four inches in diameter in captivity, although the spines can be a foot in length in the wild (seldom longer than eight inches in the aquarium). They prefer a mature tank of 50 gallons or more where there is sufficient algae growth upon which they can feed. Largely nocturnal, they may hide during the day and then come out to scour the reef by night. In addition to eating algae, they will feed on small animals and some detritus. D. setosum is compatible with most other marine species and is considered reef-safe. Urchins can play an important role as part of a reef tank’s clean-up crew because they are outstanding herbivores. As Dr. Ronald Shimek writes, “Sea urchins are to most shallow subtidal marine ecosystems what grazing animals such as bison or cows are to terrestrial communities.” In fact, they are so good at eating algae that they have been known to plow through your carefully cultivated coraline algae without hesitation. They have also been known to damage polyps. While this behavior may scare some aquarists away, it really shouldn’t, as the urchin’s trail through well established coraline algae can be quite aestheically pleasing in and of itself AND it is thought to stimulate more growth. Caring for D. setosum is about as easy as it gets. Drip acclimate them, and be sure to maintain good water quality at all times. Be careful with copper-based medications—urchins do not tolerate metals well. In terms of diet, a mature aquarium with plenty of algae may suffice. Anecdotally, their diet can be supplemented with small pieces of meaty marine food such as table shrimp or mussels, and some aquarists have fed them Caulerpa. Bob Fenner also recommends Tetra Tips for urchins. One final note, D. setosum can harm the aquarist both chemically and physically. Their sharp spines can become imbedded in your skin causing a painful wound (frequently akin to a bad bee sting in most humans). Be careful if you need to move them. It is easiest perhaps to coax them into a cup rather than using a net (because of their spines). Adiitional Resources: "Sea Urchins, A Testy Subject" by Shimek "Some Spines Now! Sea Urchins" by Fenner Other Marine Aquarium Articles by Ret Talbot
The copyright of the article Black Longspine Urchin in Other Invertebrates is owned by Ret Talbot. Permission to republish Black Longspine Urchin in print or online must be granted by the author in writing.
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