Moon Polyps are quite distinctive, they form a tight cluster of polyps growing in the shape of a half moon!
The Moon Polyps Palythoa sp., also known as Sea Mats or Encrusting Anemones, are colonial anemones. These zoas are very common in the aquarium trade, but there is quite a variety within this genus. Their polyps are short and partially embedded in the mat, and each polyp has a broad, flat oral disc rimmed with tentacles. The tentacles of some species are short and knob-like, while on others they are thin, long and tapering. Their colors can be cream, coffee, white, brown, or yellow, as well as other shades.
Palythoa sp. have polyps that are connected through a mat, called the coenenchyma. They incorporate bits of sand or sediment into the mat, making it more rigid to support the colony. This debris makes up for about 45% of their weight. They grow in convex shapes (1/2 moon), with each colony growing from 4″ to 12″ (10 – 30 cm) across.
What makes the Palythoa genus unique, is that their polyps are so embedded in their “mat” that they can completely withdrawal into it if they wish. This leaves behind what appears to be a rubbery encrusting surface with holes all over. This encrusting sea mat gives the appearance that the coral is a single organism.
They are fast growers and in the wild, clusters of colonies will encrust large areas of the reef with their mats. They are similar to the Protopalythoa genus, but the polyps of the Palythoa genus are smaller and generally have fewer tentacles surrounding the rim of the oral disc.
Moon Polyps are easy to care for as long as they have adequate lighting and good water flow. A strong light source is required for these corals to do well, but they will still grow slowly without it.That being said, the Palythoa genus will bleach out if the lighting is too intense. They will do well with a medium to high water flow. They are not an aggressive species, but they will grow and cover the substrate upon which they live, and overtake and encrust close neighbors. Filamentous algae can be a problem, as it can smother them. As with most zoanthids, mushroom anemones should not be placed nearby.
The Palythoa sp. are recommended as a beginner’s coral, but with some caution. Palythoa produce palytoxin, one of the most potent poisons known to science. For this reason one should take care when handling them. Don’t handle them if you have cuts or open wounds and make sure to clean your hands after handling.
Distribution / Background
Palythoa Coral Information: The Palythoa genus was described by Lamouroux in 1816. There are around 49 species in this genus. The Atlantic Palythoa include P. caribaeorum and P. mammillosa and some Pacific Palythoa are P. caesia, P. psammophila, and P. tuberculosa.
Common names the Palythoa genus is known for are Moon Polyps, Encrusting Anemones, Sea Mats, Zoanthid Button Polyps, and Button Polyps. They usually survive on live rock sold in aquaria. Propagated Palythoa now come in a bright array of colors and can be a bit more costly than those collected from the wild.
Where Palythoa Corals Are Found: The Palythoa genus are common in both the Atlantic and Pacific Oceans.
Palythoa Coral Habitat: The Palythoa sp. habitat includes shallow tidal areas, subtidal areas, reef crests, and shallow surge zones, with some preferring deeper waters. All of them prefer high water movement, and thrive with good lighting.
What do Palythoa Corals look like: Moon Polyps have soft bodies covered with a leathery skin, called the cuticle, which gives them protection. Their polyps are short and partially embedded in the mat, and each polyp has a broad, flat oral disc rimmed with tentacles. Their polyps are connected through a mat, called the coenenchyma. They incorporate bits of sand or sediment into the mat, making it more rigid to support the colony. This debris makes up for about 45% of their weight. What they take in is dependent on size, not material. After a few years, will expel the material, and collect fresh.
They grow in convex shapes (1/2 moon), with each colony growing from 4″ to 12″ (10 – 30 cm) across. The polyps of the Palythoa genus are so embedded in their “mat” that they can completely withdrawal into it if they wish. This leaves behind what appears to be a rubbery encrusting surface with holes all over. This encrusting sea mat gives the appearance that the coral is a single organism.
Though the Moon Polyps have fewer tentacles than most other Zoanthids, there is quite a variety. The tentacles of some species are short and knob-like, while on others they are thin, long and tapering. Their colors can be cream, coffee, white, brown, or yellow, as well as other shades.
They are similar to the Protopalythoa genus, but the polyps of the Palythoa genus are smaller and generally have fewer tentacles surrounding the rim of the oral disc.
Descriptions for some of these types of Zoanthids:
- Palythoa caribaeorum
This Zoanthid is an Atlantic species that can be coffee, white or tan in color, with the polyps being closely packed and touching each other. Some polyps stay open, while other remain closed and the colony will grow up to .125″ (4 mm) a day. That translates to almost 5″ a month (120 mm)! Obviously, this Paly will quickly overgrows any sessile life that is nearby. They are found in shallow waters, so they enjoy intense lighting along with a strong water flow.
- Palythoa mammillosa
This is also an Atlantic species that can be golden brown to yellow in color, with plenty of space between each polyp. They have a large oral disc with tentacles that are short and round. A colony can almost look like a coral to the untrained eye. Their colonies can be 6″ (15 cm) across. They are found in shallow waters, so they enjoy intense lighting along with a strong water flow.
- Palythoa caesia
This Zoanthid is a Pacific species that can be dark brown, tan, or white in color, and also has space between each polyp. Colonies are usually less than 4″ (10 cm) across, but several colonies can be next to each other, thus covering a much larger area. They are found in shallow waters on reef crests as well as subtidally, so they enjoy intense lighting along with a strong water flow.
- Palythoa psammophila
This too is a Pacific species that can be light brown to green in color, which almost glows under actinic lighting. Their oral disc has radiating fine lines, with the tentacles being hair like. They are often found partially buried in the sand. This should indicate a tolerance for a lower water flow and medium lighting.
- Palythoa tuberculosa
Another a Pacific species that are light chocolate in color, and form a honeycomb pattern. They feed at night, with the majority of the polyps being closed during the day. They ar found in many habitats that include shallow to deep water that has low to high flow. These are the least picky of the five mentioned here.
Difficulty of Care
Palythoa Coral Care: The Palythoa genus is easy to care for as long as they have adequate lighting and good water flow. That being said, the Palythoa genus will bleach out if the lighting is too intense. Be cautious of filamentous algae as it will overgrown and smother polyps.
They are a recommended beginner’s coral, but with some caution. Palythoa produce palytoxin, one of the most potent poisons known to science. For this reason one should take care when handling them. Don’t handle them if you have cuts or open wounds and make sure to clean your hands after handling.
There are a couple of cautionary items to be aware of when you keep Zoanthids:
The members of the Zoanthidae family have varying degrees of poison called palytoxin. All of the Palythoa genus and most Protopalythoa genus produce a high level of this poison in their mucus and gonads. Other genera, such as the Zoanthus genus, have it to a lesser extent, and so a less dangerous degree.
To be affected by this toxin, it must either be ingested or must enter the bloodstream. It can enter the system through an open wound. It has been suggested by some that it may also be absorbed through skin contact though this is not confirmed.
The danger to the aquarist is minimal with proper precautions. If you have a cut on your hand, this poison can get into your system, but in average aquarium keeping it is unlikely to pose any danger beyond a localized skin reaction. Some hobbyists wear gloves when handling these organisms.
Here’s a couple interesting facts!
Fish that eat Paly polyps, like the filefish, can bring this palytoxin in to the human food chain. This would be when a predator of the filefish is a fish that is typically eaten by humans.
Also, Pacific tribes used to use this neuromuscular poison to paralyze enemies and prey animals by coating their spears with the mucus of these corals.
- Vibrio Infection
Vibrio can at times be in the coral mucus, thus causing a Vibrio infection in humans if care is not taken. Most people have no problem, but caution and common sense play a role here. Wearing gloves and possibly goggles may be the safe route to go. After handling a Zoanthid, make sure the mucus is not on your glove or hand before handling any other corals!
Foods / Feeding
Palythoa Coral Feeding: In the wild, Palythoa corals have developed several feeding strategies. Through a symbiotic relationship with a marine algae, known as zooxanthellae, they receive the majority of their nutrients. They also capture planktonic organisms and microscopic food particles from the water column, and can absorb dissolved organic matter.
In captivity the Moon Polyps largely depend on their zooxanthellae for energy. They will need bright lighting to supply this type of nourishment. They can also be fed live brine shrimp that has been fortified, baby brine shrimp, or small amounts of freeze dried plankton.
Stable tank conditions are needed to keep the Palythoa genus. Doing water changes of 20% a month or 10% biweekly is needed, although it is suggested that doing 5% water changes once a week will replenish many of the needed additives. Make sure iodine is present, and also the addition of trace elements may help with the Moon Polyps survival.
Suggested levels for Palythoa species are:
- Calcium: 380 – 430 ppm
- Alkalinity: 3.2 – 4.8 MEQ/L (8 to 11 dKh – 10 is recommended)
- Phosphates: 0, zero.
- Magnesium: 1250 – 1300 ppm.
- Strontium: 8 – 10
|Quick Reference Chart
A typical live rock/reef environment is what is needed for your Moon Polyps, along with some fish for organic matter production. A mature tank (well over a year old) is advised to increase the successful keeping of Palythoa.
Provide proper lighting and water movement. Moderate water flow and a strong light source are required for Moon Polyps to do well. These colonial anemones are not an aggressive species. They get along well with their own kind, but space should be provided between them and other corals as they are fast growers and will overtake close neighbors.
- Minimum Tank Size / Length: 10 gallon Nano (38 L) or larger
- Marine Lighting: Medium to high. Will tolerate all levels, but most can handle high levels.
- Temperature: 72° – 83° F (22° – 27° C)
- Salinity / Specific Gravity: 1.023 – 1.025
- Water Movement: Moderate for some, but most prefer high
- Water Region: All areas of the aquarium
Compatibility and Social Behaviors
The Palythoa genus will get along with itself, but does need to be placed in an area where they will not encroach on nearby corals. They should be kept well away of any stony coral, as they grow very quickly and will smother sessile corals for space.
Moon Polyps are not an aggressive species. They can be kept in the company of small peaceful coral reef fish and shrimp, and hermit crabs. Other good tank mates include small tangs and blennies that will feed on filamentous algae. Avoid large crustaceans, large angelfish, and most butterflyfish. Sea Anemones and Tube Anemones should also be avoided. There is also a sea slug from the Aeolidiopsis genus that feeds on Palythoa.
Sex – Sexual differences
Breeding and Reproduction
Propagation is rather simple for Palythoa corals, simply cut the mat or chip away under the polyp’s grip. They can be out of the water a few minutes with no ill effects. Dry the bottom of the mat or debris that the polyp is stuck to, and the rock or plug you will be putting it on. Then use super glue (the gel is the best) to connect them. Wait a few seconds for it to set and then put the new frag back into the water. Another method that can be used is to rubber band them to a rock or desired surface. By the time the rubber band breaks away, the zoanthid will have connected.
The Palythoa genus is generally hardy and durable if provided with a proper reef environment. However be cautious of filamentous algae as it will overgrown and smother polyps. Also, Intense light can cause bleaching.
A snail called the Box Snail or Sundial Snail Heliacus areola preys on Zoanthid colonies, so must be removed if seen. There is also a sea slug from the Aeolidiopsis genus that feeds on Palythoa. Avoid large crustaceans and aufwachs feeders, such as large angelfish and most butterflyfish, that like to nibble on their tentacles.
Palythoa Corals for Sale: The Moon Polyps or Sea Mat Palythoa sp. are very easy to find at pet shops and on line. Online they can run about $6.00 up to $100.00 USD or more for a small grouping, depending on the color and size.
- Animal-World References: Marine and Reef
- Eric Borneman, Aquarium Corals : Selection, Husbandry, and Natural History , TFH Publications, 2001
- Helmut Debelius and Hans A. Baensch, Marine Atlas Volume 1 (Baensch Marine Atlas), Microcosm Ltd, 1997
- Ronald L. Shimek, Guide to Marine Invertebrates: 500+ Essential-to-Know Aquarium Species, Microcosm, 2005
- Bob Goemans, Zoanthids, Animal Library, Saltwatercorner.com
- Rudman, W.B., Feeding on Palythoa, Sea Slug Forum, Copyright © Australian Museum, 1998-2008