---
title: Encrusting Sea Mat (Palythoa mutuki)
scientific_name: Palythoa mutuki
common_name: Encrusting Sea Mat
taxon: Zoanthids
published: 2026-08-10T20:57:58.983Z
updated: 2026-08-10T21:05:34.999Z
tags: Encrusting Sea Mat, Palythoa mutuki, Zoanthids, Red Sea, Marine Life, Diving
url: https://redseacreatures.com/taxon/invertebrate/stinging/zoanthids/encrusting-sea-mat
---

# Encrusting Sea Mat (*Palythoa mutuki*)

## Quick facts

- **Group:** Zoanthids (*Zoantharia*)
- **Size:** polyps to 1 cm, colonies to 50 cm across
- **Depth:** 0-15 m
- **Diet:** Filter feeder
- **Activity:** Diurnal
- **Rarity:** Common
- **Habitat:** Shallow rock and reef flats in strong light
- **Reproduction:** Broadcast spawner, Budding, Gonochoric
- **Hazard:** Poisonous

## How to recognise it

- polyps standing slightly apart, each on its own short column
- brown to olive, opening as flat discs with short tentacles
- sandy, gritty body wall
- shallow rock in bright light

Brown to olive polyps, each about a centimeter across, standing slightly apart on short columns and joined by a thin shared base - looser than the solid carpets its relatives form, so the rock shows between them. Open polyps look like flat discs fringed with short tentacles.

Most of the food comes from inside. Symbiotic algae packed into the tissue photosynthesize and pass over sugars, which is why colonies grow where light is strong and why they close up and look like nothing much when the sun goes. Plankton caught by the tentacles is a supplement rather than the meal.

The genus is the one to know about for the wrong reasons. Palythoa gave its name to palytoxin, one of the deadliest non-protein compounds known, discovered in a Hawaiian species used to poison spear tips. Poisonings today come from aquarium keepers scrubbing colonies in warm water and breathing the aerosol, not from divers - in the sea it is simply a mat on a rock, and looking costs nothing.

## Also known as

- **Russian:** Палитоа мутуки

## Scientific synonyms

- *Gemmaria arenacea* Wilsmore, 1909
- *Palythoa (Gemmaria) mutuki* (Haddon & Shackleton, 1891)

## Range

Japan

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*Source: [Red Sea Creatures](https://redseacreatures.com/taxon/invertebrate/stinging/zoanthids/encrusting-sea-mat)*
*Updated: August 10, 2026*