Guide to Identifying Zoanthids
Zoanthids Are Hardy Animals that are Difficult to Identify
Zoanthids make some of the best "starter corals" for the beginning marine aquarist. Here's how to identify the best ones for your aquarium.
Zoanthids are very hard to identify down to the species level. This is the reason they are frequently identified by their color, place of origin and genus name (e.g. Jakarata Halloween Zoanthid or a Blue Zoanthid, Zoanthus spp.). This article will help you learn to identify which zoanthids are best for your aquarium.
Six Tentacles Instead of Eight
Taxonomically speaking, zoanthids belong to the Phylum Cnidaria or animals with stinging cells. All corals are cnidarians, but zoanthids belong to a subset of cnidarians from the Class Anthozoa, which include three subclasses: Ceriantipatharia, Hexacorallia and Octocorallia. The first subclass includes the tube anemones, the black corals and the thorny corals while the latter two include most of what marine aquarists generally consider corals. Zoanthids are hexacorals, which is simply a descriptive term indicating that each polyp has tentacles and those tentacles occur in multiples of six. Conversely, soft and leather corals are all octocorals with eight tentacles. The aquarist can differentiate between a zoanthid and a similar looking soft coral such as a Glove Polyp (Clavularia spp.) by counting the number of tentacles.
No Hard Skeletons
Other hexacorals include sea anemones, mushroom corals and the “true” or stony corals. Zoanthids can be differentiated from the stony corals because zoanthids do not have hard skeletons. Zoanthids occur as solitary polyps, a number of polyps connected by runners or a number of polyps embedded in a mat or tissue matrix called a coenenchyme. If you look closely at a zoanthid polyp, you will see that it has an oral disc on top with a “mouth” in the center which is generally surrounded by two rings of tentacles.
There is a lot of debate regarding zoanthid classification. The Integrated Taxonomic Information System lists four families of zoanthids, but for the purposes of the marine aquarist, only two need mention: Parazoanthidae and Zoanthidae.
Family Parazoanthidae – Yellow Polyps
The most popular zoanthids from the family Parazoanthidae are commonly known to aquarists as Yellow Polyps or Parazoanthus species. The color can vary from a cinnamon-brown to a striking yellow. They generally occur in colonies of polyps that somewhat resemble champagne flutes. While they are sometimes embedded in a mat, they are more often solitary. Most yellow polyps host symbiotic zooxanthellae and, as such, are photosynthetic. Nonetheless, they appreciate target feedings of zooplankton-type foods. Give them moderate light, moderate to strong intermittent flow and supplemental feedings, and these very attractive zoanthids will thrive in your aquarium.
Family Zoanthidae –Palythoa, Protopalythoa and Zoanthus Species
There is a debate about the relationship between the genus Palythoa and the genus Protopalythoa, but species from either genus can generally be dealt with together. Button Polyps (Protopalythoa spp.) and Sea Mats (Palythoa spp.) are good examples of these beautiful zoanthids. The former is generally solitary, while the latter, as the name suggests, is frequently embedded in a mat. All of these zoanthids possess broad, flat oral discs ranging in color from a brownish-yellow to a cream color. The more desirable ones have attractive fluorescent accents and striations. These are hardy zoanthids that will readily accept target feedings but also are photosynthetic. Provide them with moderate light and moderate to strong intermittent flow, and they will quickly spread over your rocks (you may have to actually prune them to keep them from overgrowing your other corals!).
Finally, species from the Zoanthus genus are the most common and striking zoanthids in the hobby. These zoanthids are generally identified with creative names based on their color schema. They possess small polyps often with dramatic contrasting colors between oral disc and tentacles. In the proper environment, these boldly colored zoanthids are hardy and fast-growing. They rely heavily on zooxanthellae, so it is essential to give them moderate to strong lighting. They like moderate to strong intermittent flow and are the least likely zoanthids to benefit from supplemental feedings.
