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worms > Phylum Platyhelminthes > Class Turbellaria > Order Polycladida
Spangled flatworm
Acanthozoon sp.
Family Pseudocerotidae
updated Oct 2016

Where seen? Like a glittery black evening gown, this amazingly large flatworm is commonly seen especially on our Southern shores. On coral rubble, near living reefs. Seasonally, it can be plentiful, with many worms encountered during a single visit.

Features: 8-12cm long, the worm can be as large as the palm of our hand! Body generally dark on the upperside (black to brown) with lots of little bumps that are yellow or orange tipped, as well as larger white spots. Seen from the top, it has a bluish white margin, while from the bottom it has a dark broad margin against a pale foot. It has a pair of small, erect and pointed, ear-like pseudotentacles at the front, made up of folded edges of the body.

The flatworm can be quite active, especially at night. Like a stealthy spotted mat, it is often seen gliding rapidly, hugging the surface closely, ruffling the body edges as it moves. One was even swimming from one seagrass blade to another, elegantly ruffling its body edges to 'fly' through the water. Sometimes, you might come across what appears to be a very large Spangled flatworm. Look closely and it will may turn out to be two such flatworms!

Similar animals: Acanthozoon species look very much like Thysanozoon species. They are only positively identified by microscopic examination: Acanthozoon has only one male pore while Thysanozoon has two.

Swimming actively from one
seagrass blade to another.
Pulau Semakau, Jan 05

Pseduotentacles; body with little bumps.

Beting Bronok, May 09

Terumbu Berkas, Jan 10

Photo shared by Loh Kok Sheng on his flickr.

Tuas, Aug 04

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

Spangled flatworms on Singapore shores

Photos of Spangled flatworms for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

Tanah Merah, Jul 09
Photo shared by James Koh on his blog.

Terumbu Semakau, Jul 14
Photo shared by Jurian Toramae on facebook.

Terumbu Bemban, Jun 10
Photo shared by Loh Kok Sheng on his blog.

Terumbu Semakau, Dec 15
Photo shared by Marcus Ng on facebook.

Terumbu Pempang Laut, May 15
Photo shared by Heng Pei Yan on facebook.

Terumbu Pempang Tengah, Sep 14
Photo shared by Loh Kok Sheng on his blog.

Terumbu Pempang Darat, Jun 10
Photo shared by James Koh on his blog.

Terumbu Bemban, Apr 11
Photo shared by Toh Chay Hoon on her blog.

Pulau Jong, Apr 15
Photo shared by Neo Mei Lin on her blog.

Pulau Pawai, Dec 09

Pulau Sudong, Dec 09
Photo shared by James Koh on his flick.

Terumbu Salu, Jan 10
Photo shared by Loh Kok Sheng on his flick.

Terumbu Berkas, Jan 10

Pulau Biola, Dec 09

Pulau Berkas, May 10

Pulau Senang, Jun 10
Photo shared by James Koh on his flick.

flatworm swimming from SgBeachBum on Vimeo.

Penis fencing in flatworms from Loh Kok Sheng on Vimeo.

  • Newman, Leslie and Lester Cannon. 2003. Marine Flatworms: The World of Polyclads. CSIRO Publishing. 97pp.
  • Humann, Paul and Ned Deloach. 2010. Reef Creature Identification: Tropical Pacific New World Publications. 497pp.
  • Kuiter, Rudie H and Helmut Debelius. 2009. World Atlas of Marine Fauna. IKAN-Unterwasserachiv. 723pp.
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