Zoanthids

Zoanthids are a group of colonial cnidarians in the order Zoantharia, commonly referred to as zoanthids. They form soft, fleshy colonies composed of numerous polyps that share a common tissue and attach to hard substrates such as rock or rubble by a pedal disc. Unlike stony corals, most zoanthids lack a rigid calcium carbonate skeleton, giving colonies a flexible, mat-like appearance. They exhibit a wide range of colors and polyp sizes.

Most zoanthids host photosynthetic dinoflagellates, known as zooxanthellae, within their tissues, which provide energy through photosynthesis. This symbiosis links their distribution to light availability and often supports their vibrant coloration. In addition to nutrition from photosynthesis, individual polyps capture small plankton and organic particles with their tentacles.

Reproduction occurs both asexually and sexually. Asexual reproduction by budding allows colonies to expand by producing new polyps that remain connected. Sexual reproduction involves the release of sperm and eggs, producing planula larvae that settle to form new colonies elsewhere.

Zoanthids are found in tropical and subtropical shallow marine environments, commonly on exposed to moderately sheltered rocky substrates and reef flats. They are popular in marine aquariums for their bright colors and relative hardiness. In tanks, they require stable water quality, moderate to strong lighting, and adequate water flow. Some species can spread rapidly and overgrow neighboring corals.

Safety and toxins: certain zoanthids, particularly some Palythoa and Zoanthus species, contain potent toxins such as palytoxin. Handling these colonies can cause skin irritation or more severe effects if toxins are ingested or inhaled. Protective gloves are recommended when handling, and colonies should be quarantined and properly disposed of to minimize risk.