Palythoa

Palythoa is a colonial animal closely related to zoanthids and known in the hobby simply as "paly." Its polyps are larger than those of most Zoanthus; the oral disc is broad and flat, with thin, short tentacles around the edge. Many species incorporate sand and lime grains into their body wall, forming a firmer, leathery tissue. Large-polyp forms were once placed in a separate genus, Protopalythoa; today this name is a synonym of Palythoa, but it lives on in the trade.

Most colorful palys on sale are Indo-Pacific colonies of uncertain species and, as with zoanthids, are sold under trade names. Whether some forms are a "paly" or a "zoa" is debated even among sellers.

Palytoxin warning: Palytoxin is one of the most potent marine toxins known, and Palythoa colonies have been blamed for most poisoning cases among aquarists. Touch colonies only with gloves and protective eyewear; do not work with cuts on your hands, and take care that tissue fluid does not splash into your eyes while cutting. Never put Palythoa-covered rock in boiling water, and never clean it with steam or scrub it out of the water; these practices have released the toxin into the air and caused serious respiratory poisoning. If colonies need to be removed, turn off the pumps and skimmer and take them out together with the piece of rock, under water. If you develop fever, shortness of breath, muscle pain or burning in the eyes, see a doctor immediately (in Türkiye, the National Poison Information Center: 114).

• Nuclear Green: One of the most sought-after palys, with a bright green oral disc and a bluish-toned skirt.
• Purple Death: A form very similar in structure to Nuclear Green, distinguished by its colors.
• People Eater: A form known for its large polyps and the green slit in the center of the oral disc; its red-toned variant is especially sought after, and it is sometimes sold as a zoanthid.

It forms colonies on shallow reef flats, rocky shores and intertidal zones in the Indo-Pacific and the Caribbean, mostly in sunlit places exposed to wave action.

• Light: Moderate light (about 80–200 PAR). Most forms open larger polyps in low to moderate light.
• Flow: Moderate, random flow; detritus should not build up on the broad oral discs.
• Placement: The middle or lower zone of the rockwork; keeping it on its own rock reduces both spreading and the need for handling.
• Water parameters: Salinity 1.024–1.026; KH 7–11 dKH, calcium 400–450 mg/L, magnesium 1250–1350 mg/L. It does well in water with some nutrients.
• Carbon: Activated carbon has been shown to remove most of the palytoxin in the water; running carbon in an aquarium with Palythoa is a wise precaution.

It photosynthesizes, but it catches particulate food more eagerly than Zoanthus. Feeding small morsels such as mysis, chopped shrimp or fine zooplankton 1–2 times a week increases growth and polyp size.

It does not sting; however, as it spreads it can creep under other corals. Leave a few centimeters between it and other zoanthid and Palythoa colonies. It is defenseless against stinging LPS corals and anemones. Some dwarf angelfish, butterflyfish, zoanthid-eating nudibranchs and sea spiders eat the polyps.

Polyps are cut from the base with a sharp scalpel, singly or in small groups, and glued to frag plugs. Cutting must always be done under water or in a separate container, with gloves and eye protection; the tools should be rinsed with plenty of water afterward. In some forms, freshly cut pieces may look fine for a few days and then close up and melt; cutting the pieces in groups of a few polyps improves the success rate.

• Polyps closed: Pests (nudibranchs, sea spiders), sudden changes or fish picking at them.
• New frag melting: Cutting stress and too much light; let new pieces rest in shade and gentle flow.
• Brown polyps spreading unwanted: Some Palythoa that arrive with live rock can spread uncontrollably; follow the palytoxin precautions in full when removing them.