Picture of Yellow Polyps, also referred to as Parazoanthus gracilis, and colonial anemone
Parazoanthus gracilis

   The Yellow Polyps are a staple that everyone, beginners to experts, loves to have in their aquarium!

   The Yellow Polyps, often referred to as Parazoanthus gracilis, are an unusually beautiful colonial anemone. They have long thin tentacles attached to a fluted body. The polyps are individual, not an encrusting mat, and are bright yellow or gold in color. A most interesting thing about these colonial corals is that their polyps will open or close at the same time. Because of this it is believed that the individual polyps send messages to each other probably by chemical means.

   The Parazoanthus species are very common in the aquarium trade, but there is quite a variety within this genus. These common Yellow Polyps are found in the tropical Western Pacific Ocean and can be solitary or in small groupings. They live on rocks and other surfaces where there is moderate light and water movement. They catch zooplankton from the water column and may also contain the marine algae known as zooxanthellae. These will both provide nutrients that are necessary for their survival.

  Easy to care for and readily available, the Yellow Polyps can be recommended to beginners. A moderate water movement is required and they need to be fed zooplankton type foods. They can also be fed brine shrimp, chopped worms, flake food, and mysis. They will usually feed readily, though may decline food if not fed regularly. They reproduce by budding and will spread across any surface, including the aquarium glass.

  Most of the Parazoanthus sp. are not yet classified, or they are misidentified. The taxonomy of the Zoanthids itself has been very difficult. Although some species are described, it is still largely speculative. The Colonial Yellow Polyps P. axinellae is one of only a few species that has been described. The common Yellow Polyps have not yet been scientifically identified to the species level, or even to the genus level. Although they are generally referred to as Parazoanthus gracilis, this is not a valid scientific name or classification for these zoanthids.

  The Yellow Polyps are the poster child for why taxonomic placement can be such a nightmare. For two reasons they are put into the Parazoanthus genus. One is because they are yellow, which is the color of most Parazoanthus species, and the other is because they do need supplemental feeding. In fact, the only things that seems to make them similar is the color and the need to eat.

   There are several areas where the Yellow Polyps are different from Parazoanthus. Many Parazoanthus species only grow on living organisms like hydroids, gorgonians, or sponges, and need this host to survive. The Yellow Polyps usually do not, in fact they have different needs. They need moderate lighting to support zooxanthellae, which some believe they contain. They are also not picky about what you feed them, unlike Parazoanthus sp. that only will eat zooplanktonic foods. It has been an issue of debate as to where to put the P. gracilis. Some feel they are more like Acrozoanthus or Zoanthus species. For now they are an orphan, but still referred to as Parazoanthus gracilis.

   Though Parazoanthus corals are not an aggressive species, they will encroach and grow over other corals. As with most zoanthids, the Yellow Polyps should not be placed next to corallimorphs like the Discosoma sp. or other types of mushroom anemones. Filamentous algae can be a problem, as it can smother them.

Scientific name

   Family: Parazoanthidae
   Species: Parazoanthus gracilis

  Note: The Yellow polyps have not yet been scientifically identified to the species level, or even to the genus level. So this is not a valid scientific name or classification for these zoanthids.

Distribution / Background

   Parazoanthus Coral Information: The Parazoanthus genus was described by Haddon and Shackleton in 1899. Species found in the Atlantic include P. axinellae, P. catenularis, P. parasiticus, P. puertoricense, P. swiftii, and P. tunicans; species found in the Pacific include P. dichroicus. The common Yellow Polyps, often referred to as P. gracilis, also come from the Pacific, however these have not yet been scientifically identified to the species level, or even to the genus level. So this is not a valid scientific name or classification for these zoanthids.

   Where Parazoanthus Corals Are Found: The Parazoanthus genus are common in both the Atlantic and Pacific Oceans. P. gracilis are found in the tropical Western Pacific Ocean.

   Parazoanthus Coral Habitat: The Parazoanthus genus inhabits numerous locations throughout the reef. They will encrust rocks or various types of dead matter, like old worm tubes; or many will grow on living organisms like hydroids, gorgonians, or sponges. The prefix “Para” is often associated with a parasitic situation where the host views its newly found friend as a pest. In this case, though, Parazoanthus are not presumed to be parasitic to their hosts as both are believed to benefit from each other’s company.

   P. gracilis can be solitary or in small groupings. They live on rocks and other surfaces where there is moderate light and water movement. They catch zooplankton from the water column and may also contain the marine algae known as zooxanthellae. These both provide nutrients that are necessary for survival.


   The Parazoanthus genus is not on the IUCN Red List for Endangered Species.


   What do Parazoanthus Corals look like: The Yellow Polyps Parazoanthus gracilis can be found solitary or will form small colonies, but do not have a common mat that connects them. They grow on any hard surface and do not need a host to survive. They reproduce asexually by budding daughter polyps from their base. There is some debate over this, but they may contain the marine algae, zooxanthellae, and also take in food from the water column, both of which are important for survival.

Picture of Yellow PolypsYellow Polyps Parazoanthus sp. gracilis

   The P. gracilis have soft bodies covered with a leathery skin, called the cuticle, which gives them protection. Their bodies are fluted and they have long, thin tentacles. They come in a range of shades from cinnamon to yellow. Generally they are a bright yellow, but can turn brownish if the lighting is too intense.

Difficulty of Care

   Parazoanthus Coral Care: The Yellow Polyps P. gracilis are a recommended beginner’s coral. They are easy to care for but do need light and food to survive. In fact, the lighting along with feeding helps them to propagate faster. They also need moderate water movement where they can catch particles of food that are given to the fish. They are not picky eaters.

   There are a couple of cautionary items to be aware of when you keep Zoanthids:

  • Palytoxin
      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

   Parazoanthus Coral Feeding: In the wild, Parazoanthus zoanthids have developed several feeding strategies. They capture planktonic organisms and microscopic food particles from the water column, and can absorb dissolved organic matter. Unlike other Parazoanthus sp, the P. gracilis may have a symbiotic relationship with a marine algae, known as zooxanthellae, where they would receive some of their nutrients.

   In captivity the Yellow Polyps do well with crustacean and fish flesh that has been minced, along with worms that are small enough for them to grab. They do not need supplemental feeding if they are in a good water flow area that whisks by food you have put in for the fish, enabling the polyp to capture its meal.

Aquarium Care

   Stable tank conditions are needed to keep the Parazoanthus 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 Colonial Yellow Polyps survival.

   Suggested levels for Parazoanthus species are:

  • Calcium:  380 – 430 ppm
  • Alkalinity:  3.5 – 4.2 MEQ/L (8 to 11 dKh – 10 is recommended)
  • Phosphates:  0, zero.
  • Magnesium:  1250 – 1300 ppm.
  • Strontium:  8 – 10

Aquarium Parameters

Quick Reference Chart
Lighting:Prefers Low Lighting LevelsPrefers Medium Lighting LevelsPrefers High Lighting Levels
Water Flow:Prefers Low Water Flow LevelsPrefers Medium Water Flow LevelsPrefers High Water Flow Levels
Temperament:Peaceful TemperamentSemi-Aggressive TemperamentAggressive Temperament

   A typical live rock/reef environment is what is needed for your Yellow 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 P. gracilis. The Yellow Polyps are from temperate waters and need cooler aquarium temperatures, so a chiller may be needed.

   Provide proper lighting and water movement. Moderate water flow and a medium light source are required for Yellow Polyps to do well. These zoanthids 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 can overtake close neighbors.

  • Minimum Tank Size / Length: 10 gallon Nano (38 L) or larger
  • Marine Lighting: Medium to high
  • Temperature: 59° – 73° F (15° – 23° C). Parazoanthus species from tropical waters require 72° – 83° F (22° – 27° C).
  • Salinity / Specific Gravity: 1.023 – 1.025
  • Water Movement: Moderate to high
  • Water Region: All areas of the aquarium

Compatibility and Social Behaviors

   The P. gracilis will get along with itself, but does need to be placed in an area where they will not encroach on nearby corals. They can grow over other corals, so they should be kept away from sessile animals.

   Yellow Polyps are not an aggressive species. They can be kept in the company of small peaceful coral reef fish and peaceful crustaceans. Other good tank mates include herbivorous blennies that will feed on filamentous algae. Avoid large crustaceans, large angelfish, and most butterflyfish. Sea Anemones and Tube Anemones should also be avoided.

Sex – Sexual differences

   No sexual difference in appearance is known.

Breeding and Reproduction

   The P. gracilis reproduce by forming and budding off new polyps from the base of the parent.

   Propagation is rather simple for Yellow Polyps, 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.

Potential Problems

  The Parazoanthus 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.

   A snail called the Box Snail or Sundial Snail Heliacus areola preys on Zoanthid colonies, so must be removed if seen. Avoid large crustaceans and aufwachs feeders, such as large angelfish and most butterflyfish, that like to nibble on their tentacles.


   Parazoanthus Corals for Sale: The Yellow Polyps, often referred to as Parazoanthus gracilis, are easy to find at pet shops and on line. Online they can run about $16.00 USD or more, depending on size.


Featured Image Credit: Pavaphon Supanantananont, Shutterstock