Taxonomic Differences Between Soft Corals and How to Differentiate Them

Differentiating between Capnella, Cladiella, Nepthea, Lemnalia, Litophyton and Alcyonium can be a very difficult thing to do as most times these soft corals are given and classified simply as a "COLT" finger coral. When it comes to Scleractinians(stony corals), we have a much better chance of actually classifying the coral based on it skeletal makeup and design. With the octocorals(soft corals, stoloniferans, Sea Pens and Gorgonians) our ability of actually determining the species of coral that is in question becomes vague at best.

Determining whether or not a coral is a scleractinia or not is fairly easy, I will say. Even for the novice aquarist, it should be recognized that the difference between a soft or stony coral is whether or not the coral precipitates a calcareous skeleton or not. The only exception to this rule is the Order Helioporacea consisting of two families: Lithotelestidae and Helioporidae. These two families are hermatypic, meaning they form a calcium skeleton and are the only reef building octocoral.

The fact that soft corals do not have any visible skeletal features to aid in classifying and identifying the particular coral places significant trial and error into the equation in actually identifying the coral. Many times a generic name will be associated with a particular coral such as "brain coral" or "colt-finger leather coral". Their are other times when the name isn't even correct in the identification at all. Pachyclavularia(green star polyps) are sometimes confused with Briareum(Pacific encrusting gorgonian) and they are used interchangeably though Briareum often form short upright fingers or lobes from their encrusting base, not evident with the stoloniferan Pachyclavularia. The mat of a briareum is also usually a purplish gray to greenish brown color whereas pachyclavularia has a purple/red mat.

The identification of soft corals is best described as corals that lack a calcareous skeleton and which possess polyps with eight tentacles and feathery pinnules along the edges. Once this has been established you can then break down Octocorals further. Whether the soft coral is branching, encrusting, finger appearance, stalked or lobed.

Next you can determine whether the coral is monomorphic or dimorphic? One or two sets of polyps with monomorphic consisting of just autozooid polyps used for feeding purposes and sexual reproduction. Or the presence of both autozooid and siphonozooid polyps that looks like small bumps on the corals surface and is responsible for water flow within the colony. An example of a monomorphic coral would be Xenia, while an example of a dimorphic coral would be Lobophytum.

The features that are characteristic of the soft coral can also help you to narrow down your definition and true name of the coral in question. Such features as slippery in appearance, sclerites visible through the tissue as in Dendronephthya, colony soft or firm to the touch, do the polyps contract or collapse and does the coral have a rough or smooth appearance to it, is the coral zooxanthellate or azooxanthellate and does the colony drop branchlets like Capnella coral are some ways but not all of the ways to aid in the accurate classification of the coral.

Lastly you can remove a section of the base/stalk of the soft coral to view under a microscope to determine the type of coral based on the size, number, color, arrangement and shape of the spicules of calcium carbonate called sclerites. These sclerites may be loosely present in the coral as is the case with Xeniidae species, or close together as is evident in Sinularia or even fused together as is seen in gorgonians axial material. Upon viewing these sclerites under the microscope, the pattern of the bumps, shapes and protuberances(tubercles) must be considered as well in capturing the exact species or genus of the particular octocoral, which unfortunately isn't an easy task, especially to the novice aquarist!

Unfortunately, the identification of some corals, mainly soft corals, is not cut and dry, so by taking a look at some of these variables, you can better achieve your goal of accurately determining the naming your corals.