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Phylum Mollusca > Class Gastropoda > sea slugs > Order Notaspidea
Sidegill slugs
Order Notaspidea
updated May 2020
Where seen? Some species are sometimes seen on some of our shores.

What are sidegill slugs? Sidegill slugs belong to Phylum Mollusca and Class Gastropoda like other snails. Sidegill slugs belong to Order Notaspidae are NOT nudibranchs, which belong to a different Order Nudibranchia.

Features: These slugs have a large plume-like gill between the mantle and the foot, usually on the right side of the body. They have a pair of tentacles (called rhinophores) made up of rolled up skin, and a plough-shaped structure (called the oral veil) in front of the head. Some sidegill slugs have an internal shell, others an external shell while one family does not have a shell at all. Many secrete sulphuric acid to deter predators. Most are found in shallow waters.

What do they eat?
These slugs are carnivorous and have strong jaws with a broad radula. Most feed on sponges, some also feed on hard corals and ascidians. Some even eat other slugs and fishes.

Some Sidegill slugs of Singapore

Forskal's sidegill slug

Moon-headed sidegill slug

Other sightings on Singapore shores

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

Pleurobranchea brockii
Changi, May 17
Photo shared by Jianlin Liu on facebook.

Order Notaspidea recorded for Singapore
from Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist of The Molluscs of Singapore.
+from our observation
^from WORMS

  Family Pleurobranchidae
  +Pleurobranchea brockii

Pleurobranchus forskalii
(Forskal's sidegill slug)

^Order Pleurobranchomorpha

  ^Family Pleurobranchidae
  +Berthellina delicata
+Euselenops luniceps (Moon-headed sidegill slugs)

  • Rene Ong, Tan Siong Kiat, Toh Chay Hoon, Martyn E.Y. Low & Henrietta P. M. Woo. 31 Mar 2017. First record of side-gilled slug, Berthellina delicata, in Singapore. Singapore Biodiversity Records 2017: 45-46.
  • 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.
  • 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.
  • Coleman, Neville, 1989. Nudibranchs of the South Pacific Vol 1. 64 pp.
  • Kuiter, Rudie H and Helmut Debelius. 2009. World Atlas of Marine Fauna. IKAN-Unterwasserachiv. 723pp.
  • Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore. National Council on the Environment. 163pp.
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