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Acoel worms
awaiting identification
Order Acoela

updated Oct 2016

Where seen? These tiny flattened worms are often seen on other animals, usually cnidarians such as hard corals of various species and corallimorphs.

What are aceol flatworms? They are unsegmented worms that belong to Class Acoela. Some put them in Phylum Platyhelminthes like the other larger flatworms.

Features: 1cm long or less. Often circular in shape and brown, sometimes with a white stripe or short white line or a yellow spot. The brown colour comes from the symbiotic algae in their bodies. Many species reproduce asexually by fragmentation.

What do they eat? It is believed that they graze on the edible bits that get trapped in the mucus produced by the host animals that they are found on.

What eats them? Among their predators are tailed slugs (Family Aglajidae).

A hard coral thickly covered
with acoel worms.
Pulau Semakau, Oct 11

On Small goniopora coral.
Tuas, Dec 03

On Anemone coral.
Pulau Semakau, Aug 11

Acoel worms on Singapore shores

Photos of Acoel worms for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

On Button zoanthid.
Terumbu Semakau, Dec 15
Photo shared by Toh Chay Hoon on facebook.

  • Gosliner, Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral Reef Animals of the Indo-Pacific: Animal life from Africa to Hawaii exclusive of the vertebrates Sea Challengers. 314pp.
  • Newman, Leslie and Lester Cannon. 2003. Marine Flatworms: The World of Polyclads. CSIRO Publishing. 97pp.
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