Colonial Zoanthid, Palythoa ignota

Colonial Zoanthid, Palythoa ignota. Underwater photograph taken in Bahía Concepción, Baja California Sur, October 2024.  Photograph and identificaiton courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:   The Colonial Zoanthid, Palythoa ignota Carlgren, 1951, is a hexacoral in the Sphenopidae family of colonial anemones. The genus Palythoa is one of only two genera in that family, and there are ninety species in this genus. In Mexico, this species is known as zoántido colonial.

Morphology:  Colonial Zoanthids grow as a colonial mat of individuals connected by a thick tissue (coenenchyme). They lack a pedal disk. The column is around 2.0 cm (0.75 inches) in length, and the disk can range from 1.2 cm (0-.5 inches) to 2.5 cm (1.0 inch) in diameter.  The oral disk is rimmed with a single row of 40 to 50 tentacles. The mouth is slit shaped compared to the round mouths of other anemone species. The column and disk are brown to olive in color. The green color comes from the zooxanthellae living in the tissues.

Habitat and Distribution:  Colonial Zoanthids are found on rocks and reef surfaces, often around tidepools. They live in the lower portions of the intertidal zone and the very shallow subtidal zone. Colonial Zoanthids have a limited distribution in Mexican waters. They are found only in the northern and central portions of the Gulf of California.

Diet:  Colonial Zoanthids are sessile predators. They feed on small invertebrates and  zooplankton, which they capture with their tentacles. Colonial Zoanthids are also zooxanthellate, meaning that they have a symbiotic relationship with single-cell dinoflagellates, known as zooxanthellae. Zooxanthellae live within certain Coral Polyps, Sea Anemones, Jellyfish, and Nudibranchs. The zooxanthellae produce energy, during daylight, by means of photosynthesis. This energy is passed along to their hosts.

Predators:  Colonial Zoanthids have stinging tentacles that provide defense from some predators. Even with this defense mechanism they are eaten by fish, crabs, and  mollusks.

Reproduction: Colonial Zoanthids reproduce both sexually, through broadcast spawning with external fertilization,  and asexually, through budding.

Ecosystem Interactions:   As zooxanthellate organisms the Colonial Zoanthids have a symbiotic relationship with zooxanthellae dinoflagellates. These zooxanthellae provide energy for the anemones and the anemone provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae. Other species within this genus are known to overgrow corals and other sessile organisms; perhaps this species does as well.

Human Interactions: Many species in this genus produce palytoxin, a highly toxic, fatty alcohol. Palytoxin is very dangerous to humans if inhaled or ingested. The presence of palytoxin within the Colonial Zoanthid has not been formally documented, however, we recommend that if handled,  it must be handled, with appropriate protective equipment.  Palytoxin is of current medical interest, having been extracted from other species, and being evaluated for the treatment of heart disease, high blood pressure and other diseases. Some zoanthids are collected by the aquarium trade but Colonial Zoanthid does not appear to be in demand. From a conservation perspective the Colonial Zoanthid has not been formally evaluated. They are fairly common and should be considered to be of Least Concern. However, they a limited distribution and local environmental threats could have a detrimental effect on the species.

Synonyms:  None