Zoanthids (Zoas)
Zoas or Zoanthids are found throughout the tropical oceans and belong to the family Zoanthidae, Zoanthidae is made up of a number of different genera. These genera include Zoanthus , Palythoa, Parazoanthus and Protopalythoa. Each genus has its own unique characteristics, such as polyp size, shape, colour and membrane, (coenenchyme) which can help with identification.
Zoanthids are also known for their ability to hybridize, which can make identification more difficult. Hybrid zoanthids can have characteristics of both parents, making it challenging to determine their exact species. This is also very funky when it comes to common names.
When identifying zoanthids, it is important to pay attention to their colour, pattern, and polyp size and shape. It can also be helpful to consult with other reef keepers or experts in the field, particularly if you come across a common name you are unsure about.
Zoanthids are known for their fast growth rate, making them a popular choice for reef aquariums. They reproduce asexually, which means that individual polyps can divide and create new colonies. This process is known as budding.
Zoanthids are photosynthetic, which means that they derive their energy from light. They do not require regular feedings, but they can benefit from occasional feedings of phytoplankton or other coral foods.
Feeding zoanthids should be done sparingly, as overfeeding can lead to poor water quality and other issues.
Zoanthids are relatively hardy corals, but they can still experience a number of issues in a reef aquarium. One common problem is zoanthid pox, which is a viral infection that causes small white spots on the coral's surface.
Other issues that can affect zoanthids, but is more related to newly imported colonies are pests such as predatory flatworms, nudibranchs, snails and spiders. Quarantining and dipping new imports is a must as with most corals.
Zoanthus
Zoanthus or zoas, have a distinct sphincter muscle around their oral opening. The others generally lack this characteristic. Some hobbyists describe this as a “round” mouth for zoas and a “slit” mouth for palys.
Additionally, zoas do not use sediment in their coenenchyme, or tissue. Their tissue is thinner and tears more easily than that of palys and protopalys.
Zoanthus are also the more colorful zoanthids, sometimes growing in bright colors of orange, blue, green, turquoise, red, etc. Zoas are likely to have contrasting colors between the tentacles and the oral disk. The polyps are grown in a mat of the coenenchyme, and they are embedded in the tissue (growing close to the mat).
Palythoa
Palythoa or palys, also grow in a mat of coenenchyme, just like zoas, with their polyps embedded. However, palys use sediment to help reinforce their tissue. If you look closely, you will see sand, shell, or crushed coral in their tissue. Many have observed that this is less obvious in aquacultured varieties. The coenenchyme is thicker for palys than it is for zoas, both to touch and to sight. Their “skin” feels rougher to the touch, as a result of the incorporated sediment. They are also often “slimier” than Zoanthus spp., with a thicker mucus coating.
Palys generally have a larger oral disc than zoas, with shorter tentacles. Their oral discs lack the sphincter muscle surrounding the oral opening that is observed in zoas, with many people observing a “slit” mouth instead of a “round” mouth. Palys tend to grow in dome shaped colonies. Their colors are typically more muted that those found in Zoanthus.
Parazoanthus
Parazoanthus or just polyps grow from just thread like mat. They have small polyp heads but very long tentacles which are capable of capturing small particles of food. The most common seen of this species is the Indonesian yellow polyp.
Protopalythoa
Protopalythoa or protopalys, are sometimes grouped with Palythoa. However, protopalys have polyps on the ends of stalks instead of embedded in the mat. Their bases are connected by the coenenchyme or even by stolons, which incorporates sediment into the tissue just like palys. The texture of their coenenchyme also feels similar. They are found as solitary corals quite frequently.
If you see palys and protopalys side by side, you will notice that protopalys have a larger oral disc, longer tentacles, and sometimes a greater number of tentacles. Their oral discs may be quite colorful under blue actinic lighting, even fluorescing, but their coenenchyme is normally brown or green in color.
The photos below shows the protopaly tentacles are obviously much longer than a paly's tentacles. When closed, you can see that the polyps are raised on tall stalks.
