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worms > Phylum Platyhelminthes > Class Turbellaria > Order Polycladida
Spangled flatworm
Acanthozoon sp.
Family Pseudocerotidae
updated Feb 2020

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 black with lots of little black bumps (known as papillae) that are yellow or orange tipped, some with a white base that gives the appearance of larger white spots. Margin white. Underside pale-whitish with a white outer margin and a black inner margin. It has a pair of small, pointed, ear-like pseudotentacles made up of simple 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 with yellow tips, some with a white base.

Two worms 'penis fencing'.
Beting Bronok, Jun 17

*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
On wildsingapore flickr

Other sightings on Singapore shores

Changi, Dec 19
Photo shared Abel Yeo on facebook.

Changi Lost Coast, Jun 22
Photo shared by Vincent Choo on faebook.

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

East Coast Park, May 17
Photo shared by Jianlin Liu on facebook.

East Coast Park-Marina East, May 22
Photo shared by Richard Kuah on facebook.

Lazarus Island, Nov 19
Photo shared by Jianlin Liu on facebook.

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

Terumbu Hantu, Jul 18
Photo shared by Loh Kok Sheng on facebook.

Cyrene Reef, Aug 17
Photo shared by Abel Yeo on facebook.

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

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

'Penis fencing'
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, Dec 18
Photo shared by Jianlin Liu on facebook.

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

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

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

'Penis fencing'
Terumbu Berkas, Jan 10

Photo shared by Loh Kok Sheng on his flickr.

Pulau Salu, Apr 21
Photo shared by Jianlin LIu on facebook.

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

Pulau Berkas, May 10

Pulau Berkas, Feb 22
Photo shared by Jianlin Liu on facebook.

flatworm swimming from SgBeachBum on Vimeo.

Penis fencing in flatworms from Loh Kok Sheng on Vimeo.

Grateful thanks to Rene Ong for sharing details and identifying the flatworms on this page.

  • Rene S.L. Ong and Samantha J.W. Tong. 29 October 2018. A preliminary checklist and photographic catalogue of polyclad flatworms recorded from Singapore. Nature in Singapore 2018 11: 77–125.
  • 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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