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Phylum Mollusca > Class Gastropoda > sea slugs > Order Notaspidea
Forskal's sidegill slug
Pleurobranchus forskalii
Family Pleurobranchidae
updated May 2020
Where seen? This humungous slug is sometimes seen, near reefs and seagrass areas. Sometimes seen buried just beneath the sand. On Cyrene, large numbers have been seen at some times of the year. According to Dr Bill Rudman, it is often found in quite large populations in shallow lagoons, reef crests and pools and sea grass beds.

Features: 20-30cm. The large slug has a body texture of flat polygonal bumps with faint white lines forming circles. Colour variable from black, dark maroon to lighter shades of brown and orange. It has a pair of tubular rhinophores on its head. The large single gill is found on the right side between the mantle and the foot. The underside is smooth and unmarked. The slug appears to secrete a slime that feels acidic and is hard to rub off your hand.

Tanah Merah, Jun 09

Pair of tubular rhinophores.

GIlls on the side.
Cyrene Reef, Jul 11
What does it eat? Although it is not known what this species eats, other species of Pleurobranchus are reported to feed on ascidians. Indeed, on our shores large numbers are sometimes seen among dense beds of Green gum drop ascidians.

What eats it? According to Dr Rudman, chitinous plates identified as the jaw plates of this sea slug had been found in the stomach of a turtle.

Baby slugs: They have been seen laying egg masses in white or pink frilly ribbons.

Many were seen in areas thick with Green gum drop ascidians.
Cyrene Reef, Jul 11

Laying egg ribbons.
Cyrene Reef, Jul 11
Forskal's sidegill slug (Pleurobranchus forskalii)
Forskal's sidegill slug (Pleurobranchus forskalii)

Forskal's sidegill slugs on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores


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

Cyrene Reef, Nov 07
Photo shared by Loh Kok Sheng on his blog.

Cyrene Reef, Oct 08
Photo shared by Tan Sijie on his blog.


Pulau Semakau, Aug 11
Photo shared by Lok Kok Sheng on his blog.

Pulau Semakau East, Jan 16
Photo shared by Loh Kok Sheng on facebook.

Pulau Semakau South, Apr 18
Photo shared by Loh Kok Sheng on facebook.


Pulau Semakau North, Jul 20
Photo shared by Loh Kok Sheng on facebook.

Beting Bemban Besar, Mar 17
Photo shared by Richard Kuah on facebook.

Terumbu Berkas Besar, Jan 10
Photo shared by Loh Kok Sheng on his flickr.

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 Colemanis 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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