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Phylum Cnidaria > Class Anthozoa > Subclass Zoantharia/Hexacorallia > Order Zoanthidea
Sea mat zoanthid
Palythoa tuberculosa*

Family Zoanthidae
updated Dec 2019

if you learn only 3 things about them ...
Each is a colony of many little animals.
Some may be highly toxic. Don't touch them!
The rubbery mat is living tissue and animals. Don't step on it!

Where seen? Like some weird rubber mat that coats rocks and rubble, this colony of animals is commonly seen on our Southern shores. It is often found in areas where waves crash onto the rocks in shallow waters. When the animals find a happy spot, the colony can cover a large area.

Features: Colony 20-40cm, each polyp about 1-2cm in diameter embedded in a common tissue. The polyp has a thick and short body column, topped by a wide oral disk edged with tentacles in two rows. When the polyps are expanded, their oral disks and tentacles may hide the common tissue. When the colony is out of water, the tentacles and oral disks are tucked into the body column, leaving on small puckered holes on the surface of the common tissue. Colours seen include brown, cream and yellow.

Coating a rock in a rubbery mat.

Terumbu Pempang Tengah, May 11

St. John's Island, May 06

Sisters Island, Jul 06
The common tissue is thick and rubbery. It also feels rough to the touch because the tissue may be strengthened by incorporating fine sand and other tiny debris. One study suggests these incorporated elements can make up 45% of the total weight of the colony!

Some sea mat species can grow rapidly, up to 0.4cm a day. They are quite aggressive and often overgrow other animals in the surrounding area. Some sea mat species have 'cracks' in the mat which are caused by clumps of polyps that are separating.

Sometimes confused with sponges, ascidians and other blob-like animals. Here's more on how to tell apart blob-like animals.

Toxic mat: Sea mat zoanthids contain the highly toxic palytoxin. It is reported that the Hawaiian natives produced poisoned arrows by rubbing the tips on the zoanthid Palythoa toxica. It is believed that the toxins are not produced by the animal but by bacteria that live in symbiosis with the polyps.

*Species are difficult to positively identify without close examination.
On this website, they are grouped by external features for convenience of display.

Sea mat zoanthids on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Terumbu Buran, Nov 10
Photo shared by James Koh on flickr.

Pulau Biola, Dec 09

Terumbu Berkas, Jan 10

Pulau Pawai, Dec 09

Pulau Salu, Aug 10

Pulau Salu, Aug 10


Pulau Senang, Aug 10

Terumbu Salu, Jan 10

Pulau Salu, Jun 10

Pulau Sudong, Dec 09
Photo shared by Loh Kok Sheng on his flickr.

Pulau Berkas, May 10

Terumbu Berkas, Jan 10

South Cyrene, Oct 10

Terumbu Bukom, Nov 10

With grateful thanks to Dr James Reimer of JAMSTEC (Japan Agency for Marine-Earth Science and Technology) for identification of these zoanthids.

  • Borneman, Eric H. 2001. Aquarium Corals: Selection, Husbandry and Natural History T.F. H Publications. 464 pp
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