Heteropsammia cochlea - Walking Dendro
A "New" Coral Species for the Saltwater Aquarium Hobbyist
The family Dendrophylliidae is made up of some very real aquarium favorites, but the one that is getting the most attention as of late is a species commonly called a “walking dendro” from the genus Heteropsammia. This coral is relatively new to the hobby, and it is quite unusual, to say the least. While it looks a little like a duncan polyp (Duncanopsammia axifuga) or Balanophyllia, it actually, as its common name implies, has the ability to move about the aquarium. More accurately, the worm, with which it lives in a commensal relationship, moves around the aquarium, but we’re getting ahead of ourselves.
Unusual within the Family Dendrophylliidae
The family Dendrophylliidae is a large group of corals that includes several genera with which the reef aquarist is most likely familiar. For example, it is fairly common to see Tubastraea species (cup coral or sun coral), Duncanopsammia species (whisker coral), and Turbinaria species (pagoda coral, cup coral, scroll coral, vase coral, and/or turban coral) available for sale in the North American marine aquarium trade. It is only recently, however, that Heteropsammia have been available (late summer/early fall 2009).
Most corals in the family Dendrophylliidae, which are all hexacorals, are aposymbiotic, meaning that they lack photosynthetic algae known as zooxanthellae (e.g., Tubastrea spp.). As such, most dendrophyllids feed almost exclusively through prey capture in the water column. Those species contained within the genus Heteropsammia, however, do often host zooxanthellae and many are photosynthetic. Having said that, those specimens living at depth or in sub-tropical or temperate zones may indeed be azooxanthellate, so it is likely that all specimens have a relatively good prey capture mechanism by way of their tentacles that are extended at night.
Commenal Sipunculid Worm
Zooxanthellae are not the only organism with which H. cochlea lives in a symbiotic relationship. As was mentioned above, this coral moves about the aquarium with the help of a sipunculid worm (Aspidosiphon corallicola) commonly called a peanut worm. The relationship is a commensal relationship whereby the coral benefits from the presence of the worm, while the worm receives no real benefit. The benefit to the coral is that, as a free-living coral frequently inhabiting muddy or other soft substrate, the animal would most likely be buried without the worm moving it about.
The so-called walking dendro begins life on the back of a small shell, where one or two corallites usually form. Over time, the shell is fully encrusted, and the worm, which takes up residence, uses the coral’s base for protection. The worm’s probing of the substrate is what causes the coral to move about.
Heteropsammia cochlea Husbandry
Caring for this coral is not difficult so long as the animal’s basic needs are understood. Many aquarists prefer to keep H. cochlea in a biotope tank, rather than a general reef tank, as the coral’s ability to move about the bottom of the aquarium can place it at risk in a community reef setting with other aggressive corals. In the wild, walking dendros are frequently found in high density populations with as many as three hundred individuals in a square meter. While H. cochlea is often found living adjacent to the fungiid Cycloseris cyclolites and side-by-side with Heterocyathus aequicostatus, this coral may be seriously damaged if it comes into contact with other sand-dwelling corals in a non-biotope-specific community reef.
As was noted above, H. cochlea is one of the few species of coral in the Dendrophylliidae family that contains symbiotic algae, but it is a good idea to also offer this coral supplemental target feedings. Reef aquarist have reported the most success with keeping this species in an aquarium with moderate to bright reef-ready lighting and providing target feedings at least two to three times per week.
While the aquarist is most certainly acquiring the coral, he or she ought to give some thought to the worm’s husbandry needs as well. As such H. cochlea should be kept in a tank with a mature sandbed. In addition, the aquarist should consider a longer than normal drip acclimation to insure the health of the worm. While the demise of the worm will not harm the coral in the aquarium (unless it is buried), it would certainly be a shame to miss out on the fascinating commensal behavior which gives the walking dendro its name.