In the Caribbean there are two species commonly known and described, Zoanthus sociatus and Z. pulchellus. In south Florida there are two additional species apparently never formally described. One of these undescribed species (Zoanthus n.sp. 1 in my photos) lives only intertidally, on rocky jetties at inlets where the ocean feeds into the intercoastal waterway. It forms continuous thick sheets of coenenchyme with the polyps imbedded, and the colors of the polyps sometimes include fantastic combinations in bright hues. This species is commonly mixed with Z. sociatus and Z. pulchellus where it occurs, and it is easily distinguished from them. The other undescribed species (Zoanthus n.sp. 2 in my photos) forms very small colonies of just a few to perhaps a few dozen polyps, usually on hardbottom reefs in sandy areas. The polyps are spaced widely and connected by a stolon. They are typically bright green, but may also be dark blue-gray or sometimes brilliant turquoise blue. The polyps are small and flattened, considerably smaller in diameter and height compared to Z. sociatus. Zoanthus sociatus forms large colonies of polyps connected at their bases by a very thin coenenchyme, so loosely connected are they that individual polyps or clumps of polyps readily break off of a colony if tugged. The coloration is variable but is generally shades of green or blue-green, often with a yellowish oral cone. Zoanthus pulchellus is found mainly on offshore coral reefs, though it can occur in inlets. It has larger polyps than Z. sociatus, and perhaps larger than any other species of Zoanthus. Zoanthus pulchellus readily accepts food while Z. sociatus does not. Zoanthus pulchellus is also more variable in coloration, being shades of green, gray, pink, or fluorescent red. Colonies of this species may cover large areas of reef substrate, particularly on back reef rubble.

Several species of Zoanthus are commonly imported for the aquarium trade mainly from Indonesia and Singapore. Based on their similarity to two of the Caribbean species it seems to me that some of them may have circumtropical distributions, though I have not seen anything in the literature to suggest that is the case.

Protopalythoa:

Members of this genus were previously referred to as Palythoa spp. in scientific and aquarium literature. Muirhead and Ryland (1985) separates this genus from Palythoa, which has its polyps deeply embedded in the coenenchyme. The fact that there are species with intermediate structure, such as Palythoa mammillosa, suggests that this distinction is of questionable significance. Borneman (1997) also discusses this issue. Nevertheless the majority of species of Palythoa can readily be distinguished from Protopalythoa based on this characteristic. Protopalythoa spp. have the largest polyps of all the zoanthids. They have slimy thick tissue, often with some sand grains trapped on the lower portions of the columns of each polyp. Protopalythoa spp. may occur on reef slopes, but are most common on sandy reef flats and hardbottoms in shallow or deep water. Most species are brownish, sometimes with green oral discs. Some varieties have striped or mottled oral discs. These zoanthids always remind me of the insect-eating plant known as “Venus flytrap,” since they have tapering tentacles around the margins of the oral disc quite like the pointed “eyelashes” that fringe the food capturing structures of the aforementioned plant. The plant and zoanthid polyps also slowly close around their prey in a similar fashion. Protopalythoa spp. have symbiotic zooxanthellae and must be kept under moderate to strong illumination to thrive.

Protopalythoa spp. have toxic mucus that is able to destroy scleractinian coral tissue, so be careful not to place colonies where they are likely to contact stony corals. I'll discuss this toxic mucus in more detail later in the article.

Protopalythoa spp. all take food when it is offered. They feed on meaty things such as shrimp, worm, or mollusk flesh, and will also take fish eggs, invertebrate eggs, flake foods, and pellet foods.

Three easily identified species are worth distinguishing from the rest, Protopalythoa grandis, P. psammophila, and P. vestitus. My favorite is Protopalythoa grandis, which has polyps up to two inches in diameter, and mottled in shades of brown, white, and green. It apparently has circumtropical distribution (Colin and Arneson, 1995), but colonies harvested for the aquarium trade come mainly from deep hardbottom reefs in the Gulf of Mexico off the Florida coast. To grow this species it is necessary to offer food regularly. Without adequate food supply the polyps shrink slightly and the fringe of tentacles degenerates to the point that the polyps could be confused with Discosoma spp. Protopalythoa grandis has a habit of closing up for several days, during which time it secretes a waxy film that is subsequently shed. This is a normal process that is also seen in Palythoa spp., other (but not all!) Protopalythoa spp., as well as in leather corals such as Sarcophyton and Lobophytum, gorgonians such as Pterogorgia, and the stony coral Porites. Shedding this waxy film is a means of preventing the growth of algae or other organisms on the surfaces of the polyps. Protopalythoa grandis should be placed near the bottom of the aquarium where the illumination is not very intense.

Protopalythoa psammophila ranges across the Pacific and has the desirable feature of being bright fluorescent green. At one time this species was harvested from Hawaii for the aquarium trade, but such harvest ended in the early 1990's due to new regulations for the state. Many aquarists still grow and propagate the Hawaiian form, but bright green Protopalythoa cf. psammophila are also now occasionally being imported from Singapore and the Sea of Cortez. This species prefers bright illumination, but the most intense color develops under moderate illumination.

Protopalythoa vestitus is a beauty that is widespread in the Indopacific. It has a distinctive pattern of brown and white bands on the oral disc, and may fluoresce green under blue light. It is commonly imported from Indonesia.

Palythoa:

Members of this genus all look more or less the same, quite like faviid corals with which they are often confused. As mentioned previously, the coenenchyme is thickened into a cushion in which the polyps are embedded. The coenenchyme also contains sand grains. The color is usually pale yellow or brown, but fluorescent green colonies occur in some regions, and I observed some with fluorescent orange pigment in the Solomon Islands. A small colorful crab, Platypodiella, is associated with this zoanthid and apparently feeds on it, potentially obtaining a benefit from the toxin(s) the zoanthid produces (Delbeek and Sprung, 1997).

Palythoa spp are most common on reef flats or the tops of reefs, where they may form colonies several metres across. They often occur in a zone mixed with fire corals (Millepora spp.). They may also occur on reef slopes, usually as small colonies. Degraded reefs may become overgrown by them, and they are able to out-compete stony corals.

In the aquarium one should be careful not to place Palythoa where it will contact stony corals. Palythoa spp. grow best under strong illumination, and should be offered planktonic foods, such as copepods, Artemia, or Daphnia.

Isaurus:

Members of this genus are commonly called "Snake Polyps.” Three valid species are known, I. tuberculatus, I. cliftoni, and I. maculatus. Isaurus tuberculatus is distributed circumtropically and is the species most commonly seen in the wild and in aquariums. Isaurus spp. have elongate columns with tubercles (bumps) and the columns are typically oriented so that the ends face downward. The tentacles are normally retracted during the day and expand at night to feed on zooplankton. The columns contain zooxanthellae and should be exposed to bright light. Isaurus does not need to be fed to be maintained in captivity, but regular feeding will cause the polyps to multiply. The best foods for Isaurus are Daphnia, Cyclops (copepods), and brine shrimp nauplii.

Yellow Polyps:

Although various aquarium references have called this zoanthid a Parazoanthus sp., it is not. That description makes sense when one considers that Parazoanthus spp. are often yellow. For example, several years ago when I discussed "the yellow photosynthetic zoanthid from Indonesia" with world zoanthid expert J. S. Ryland, he assured me that it was probably a Parazoanthus, but he cautioned that his comment was based on the color I described only, not on a specimen. This zoanthid does not yet have a name, nor even a genus. It appears to be related to Acrozoanthus and the undescribed zoanthid I am calling Zoanthus nsp.? in this article.

Despite its lack of taxonomic placement, this zoanthid has had a place in aquariums since the very beginning of the reefkeeping hobby. It is a very hardy beautiful addition to any aquarium. The only downside is that it spreads quickly enough to damage and overgrow corals. Take care to place this species on isolated rocks in the sand or on the glass to avoid having it grow on the reef and approach corals. Care of yellow polyps is simple: give them strong light and feed them. If they are placed in strong water motion they will catch the food offered to the fishes, and do not need supplemental feeding. They eat flakefood, shrimps, worms, or anything meaty and small enough for them to grab.

Acrozoanthus:

One species in this genus is frequently imported under the common name “Stick Polyps.” The name arises from the parchment like “stick” on which these polyps occur naturally. The stick is not secreted by the polyps themselves, but is instead the top of a tube formed by a large type of polychaete worm (Eunice tubifex) that lives buried in sand. The collectors simply cut off the top of the tube, leaving the worm intact in its home buried in the sand.  It can readily build a new extension of its tube upon which more Acrozoanthus can settle.

Acrozoanthus polyps are similar to those of “Yellow Polyps,” but they are larger, brown, and have very long stringy tentacles. Though naturally associated with the worm, these polyps readily adapt to captivity and spread onto rocks. They need to be fed to really proliferate in captivity. They will eat copepods and any chopped meaty foods. Despite their need for food, they do also harbor zooxanthellae, so they should be maintained in a well illuminated aquarium.

Neozoanthus:

This uncommonly seen genus forms small colonies of cryptic polyps that are similar in appearance to those of Epizoanthus. They characteristically have sand grains trapped in their tissue. They should be fed with copepods or brine shrimp nauplii, and provided with moderate to strong illumination. I first observed this species as a few polyps on the base of a Sarcophyton sp. from Indonesia.