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Phylum Mollusca > Class Gastropoda > sea slugs
Moon-headed sidegill slug
Euselenops luniceps
Family Pleurobranchidae
updated May 2020
Where seen? This comical cartoon-like slug is only sometimes seen. When seen, often several are seen at the same time. And then none for some time. Elsewhere, they are found in sandy and silty shores. It was previously placed in Order Notaspidae, but is now placed in Order Pleurobranchomorpha.

Features: 3-7cm. It is the only member of its genus and is distinctive. No other slug looks similar! Some have a dark underside, others a paler one. The small gill is on its right side which may be yellowish or white.

Changi East, Dec 12

Changi, Apr 09

Showing the gill on one side.

Changi, Apr 09
The slug is adapted for living in a sandy habitat. A broad foot and flattened body for crawling over sand or burrowing underneath. A long siphon on its back which brings fresh seawater into its gills while it is buried in the sand. With the incoming seawater the animal can also sense chemical released by potential prey nearby. It has a large oral veil fringed with lots of sensory 'hairs' on the underside to detect prey. The slug can swim for some distance by flapping the sides of its body.


Closer look at oral veil and mouth.
Sometimes mistaken for a squid or cuttlefish.

What does it eat? Although it is a predator, little is known about what it eats. Although it appears they have a particular fondness for sea anemones. It has also been described that they are often seen on sand flats at low tide where they hunt and swallow whole any invertebrates that they touch with their sensitive oral veil.

Moon-headed sidegill slugs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Changi, May 17
Photo shared by Loh Kok Sheng on facebook.

Changi, May 17
Photo shared by Marcus Ng on facebook.

Sisters Island, Jan 11
Photo shared by Loh Kok Sheng on his blog.

Pulau Hantu, May 09
Photo shared by Neo Mei Lin on her blog.

Pulau Sudong, Dec 09

Filmed on 31 Dec 08 at Sisters Islands

Moon Headed Side Gilled Slug @ Big Sisters Island from SgBeachBum on Vimeo.

Filmed on 23 Jan 11 at Sisters Islands

Moon-headed side-gill slug from Loh Kok Sheng on Vimeo.

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.
  • Debelius, Helmut, 2001. Nudibranchs and Sea Snails: Indo-Pacific Field Guide IKAN-Unterwasserachiv, Frankfurt. 321 pp.
  • Coleman, Neville. 2001. 1001 Nudibranchs: Catalogue of Indo-Pacific Sea Slugs. Neville Coleman's Underwater Geographic Pty Ltd, Australia.144pp.
  • 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.
  • 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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