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Phylum Mollusca > Class Gastropoda > sea slugs > Order Nudibranchia
Fugly nudibranch
Actinocyclus sp.
Family Actinocyclidae
updated May 2020
Where seen? This large, lumpy and rather fugly nudibranch is rarely seen. The ones encountered were on coral rubble. It is possible that they are not all that rare and that these very well camouflaged nudibranchs are just overlooked?

10-12cm long. Body tough and leathery. Gills short in a circle so they resemble a 'bubble'. The gills sit in a shallow cup or depression on the back of the body. The gills are actually branching, but appear smooth. Rhinophores stumpy. The entire animal is rather squat and unremarkable, well camouflaged against its surroundings in various colours of dull olive, brownish, yellowish. It produces some slime when handled.

Previously all were considered one species A. japonicus. Currently two species are identified. A. verrucosus has a few but large low rounded bumps (called tubercles). A. papillatus has many large rounded turbercles.

Sentosa, May 04

Stumpy rhinophores.

Stumpy gills that look like a bubble.
Sometimes mistaken for onch slugs (Family Onchididae). Onchs don't have feathery gills on their backs and are much flatter than this nudibranch.

What do they eat? Sponges. Bill Rudman has drawings of the nudibranch showing its head and mouth and how it feeds.

Tuas, Feb 07

Changi, Jun 16

Fugly nudibranchs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Tuas, Aug 09
Photo shared by James Koh on his blog.

Beting Bronok, Jul 14
Photo shared by Loh Kok Sheng on his blog.

Chek Jawa, Jan 14
Photo shared by Loh Kok Sheng on facebook.

East Coast Park Big Splash, Jun 15
Photo shared by Loh Kok Sheng on facebook.

Big Sisters Island, May 13
Photo shared by Marcus Ng on flickr.

Pulau Hantu, May 22
Photo shared by Vincent Choo on facebook.

Links References
  • Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore (pdf), Raffles Museum of Biodiversity Research, National University of Singapore.
  • Wells, Fred E. and Clayton W. Bryce. 2000. Slugs of Western Australia: A guide to the species from the Indian to West Pacific Oceans. Western Australian Museum. 184 pp.
  • Coleman, Neville. 2001. 1001 Nudibranchs: Catalogue of Indo-Pacific Sea Slugs. Neville Coleman's Underwater Geographic Pty Ltd, Australia.144pp.
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