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Phylum Cnidaria > Class Anthozoa > Subclass Zoantharia/Hexacorallia > Order Actiniaria
Swimming anemone
Boloceroides mcmurrichi
Family Boloceroididae
updated Jul 2024
if you learn only 3 things about them ...
These animals are everywhere on the shore. Don't step on them!
Don't pick them up. Their sticky tentacles will tear off in your hands.
They CAN swim but usually don't at low tide.

Where seen? Looking like an untidy mop, this anemone is sometimes seen in seagrass areas on many of ourshores. It is possibly seasonal. Sometimes, large numbers are seen (up to 10-20 animals in a trip) and then none at all. Once, we encountered an explosion of countless tiny swimming anemones (less than 1cm across) in the seagrass meadows of Chek Jawa.

 Features: Diameter with tentacles extended 5-8cm. The tentacles (3-4cm long) are thick at the base, tapering to slender tips. There are LOTS of tentacles (commonly more than 400). These hide the small oral disk and the mouth, which is on a cone. Some have a white band on the oral disk across the mouth. Sometimes, two of the tentacles near the mouth are prominently lighter. The tentacles are generally shades of brown with bands in darker brown or yellow. Sometimes those with spots, reddish tentacles or white stripes along the tentacle length are see. It has a short semi transparent body column and a small pedal disk which is not very sticky. It's scientific name is pronounced 'boll-loy-sir-roy-dee-des mac-moor-ree-eye'.

Sometimes mistaken for: Tiny swimming anemones may sometimes be confused with Seagrass anemones which have translucent tentacles with tiny spots.


Sometimes with white band next to
the mouth and two paler tentacles.
Pulau Sekudu, Jun 06
Mouth is on a cone in the centre.
Short body column and small pedal disk.
Changi, Apr 10
Does it really swim? Yes it can swim slowly by undulating its many tentacles in a coordinated manner. At low tide, these anemones are often seen loosely attached to seaweeds, or just lying freely on the ground. They are rarely seen swimming about. Possibly they are more active at high tide. Please don't pick up the anemone to force it to swim. Its sticky tentacles will come off in your hand and you may hurt the anemone.

Explosion of tiny swimming anemones.
Chek Jawa, Oct 10

Many had settled on seagrasses.

Adult (left) compared to tiny one (right).
Losing it: The swimming anemone can purposely drop of its tentacles if it is threatened. The dropped tentacle can wriggle, probably to distract the predator. This dropped tentacle can regenerate into a new swimming anemone after some time. However, almost no other anemone does this. So please don't cut an anemone into half hoping to get two anemones. You will instead get no anemone.

What does it eat? The swimming anemone harbours symbiotic single-celled algae (called zooxanthellae). The algae undergo photosynthesis to produce food from sunlight. The food produced is shared with the anemone, which in return provides the algae with shelter and minerals.

Status and threats: As at 2024, it is assessed not to be approaching the criteria for being listed among the threatened animals in Singapore.  

Reddish with spots.

Cyrene Reef, Aug 11

Reddish with bands.

Cyrene Reef, May 12

Brown with white stripes.

Cyrene Reef, May 12
Swimming sea anemones on Singapore shores
On wildsingapore flickr
Other sightings on Singapore shores

Sembawang, Oct 20
Photo shared by Vincent Choo on facebook.

Coney Island, Oct 20
Photo shared by Richard Kuah on facebook.

Punggol, Jun 18
Photo shared by Richard Kuah on facebook.

Explosion of tiny ones.
Changi SAF Chalets, May 25
Photo shared by Adriane Lee on facebook

Pulau Ubin, Dec 09
Photo shared by James Koh on his blog.

Pulau Sekudu, Oct 11
Photo shared by Loh Kok Sheng on flickr.

East Coast Park, May 21
Photo shared by Loh Kok Sheng on facebook.

Sentosa, Sep 11
Photo shared by Loh Kok Sheng on his blog.

Berlayar Creek, Oct 15
Photo shared by Lisa Lim on facebook.

Many tiny ones with few arms seen
Seringat Kias mangrove lagoon, Sep 25
Photo shared by Adriane Lee on facebook.

Pulau Tekukor, Nov 20
Photo shared by Jianlin Liu on facebook.

St John's Island, Oct 20
Photo shared by James Koh on flickr.

Lazarus, Jan 19
Photo shared by Marcus Ng on facebook.

Sisters Island, Dec 10
Photo shared by Loh Kok Sheng on his blog.

Pulau Jong, Aug 20
Photo shared by Loh Kok Sheng on facebook.

Pulau Semakau (South), Nov 24
Photo shared by Kelvin Yong on facebook.

Terumbu Raya, Jul 07
Photo shared by Marcus Ng on his blog.

Beting Bemban Besar, Oct 25
Photo shared by Kelvin Yong on facebook.

Terumbu Pempang Laut, Apr 11
Photo shared by Loh Kok Sheng on his blog.

Pulau Pawai, Dec 09
Shared by James Koh on his flickr.
Filmed on Cyrene Reef, Dec 10.

Swimming anemone @ Cyrene Reef from Loh Kok Sheng on Vimeo.
Links References
  • Checklist of Cnidaria (non-Sclerectinia) Species with their Category of Threat Status for Singapore by Yap Wei Liang Nicholas, Oh Ren Min, Iffah Iesa in G.W.H. Davidson, J.W.M. Gan, D. Huang, W.S. Hwang, S.K.Y. Lum, D.C.J. Yeo, May 2024. The Singapore Red Data Book: Threatened plants and animals of Singapore. 3rd edition. National Parks Board. 663 pp.
  • Daphne Gail Fautin, S. H. Tan and Ria Tan. 30 Dec 2009. Sea anemones (Cnidaria: Actiniaria) of Singapore: abundant and well-known shallow-water species. Raffles Bulletin of Zoology Supplement No. 22: 121-143.
  • Erhardt, Harry and Daniel Knop. 2005. Corals: Indo-Pacific Field Guide IKAN-Unterwasserachiv, Frankfurt. 305 pp.
  • 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.
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