Sidegill Slugs (Phylum Mollusca: Family Pleurobranchidae) of Singapore

Sidegill slugs or pleurobranchs (family Pleurobranchidae) are marine slugs with a feather-like gill on the right side of the slug's body between the prominent mantle and foot, and hence the common name. They have a pair of rolled rhinophores on the head, acting as scent receptors to seek out their prey. Some species feed on sessile organisms like sponges and tunicates, while others feed on motile ones like other slugs. Most species have a small and greatly reduced internal shell, though some may lack one as they mature. While they have a soft body, many species can secrete chemicals to protect themselves from predators.


The Forskal's Sidegill Slug (Pleurobranchus forskalii) is sometimes seen on our southern shores. It is thought slugs of this genus feed on ascidians. This slug has been observed to exude an acidic secretion when disturbed.


The Moon-faced Sidegill Slug (Euselenops luniceps) can swim by flapping its mantle. This species lacks an internal shell as it matures. The wide oral veil apparently has lots of tiny hair-like structures which allow the slug to sense its prey. This species can also burrow into the sand to seek food or avoid predation.

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References

• Gosliner, T. M., D. W. Behrens & Á. Valdés 2008. Indo-Pacific nudibranchs and sea slugs: a field guide to the World’s most diverse fauna. Sea Challengers/California Academy of Sciences: Gig Harbor/San Francisco, 426 pp.
• Rudman, W. B. 2012. Sea Slug Forum.  Retrieved May 10, 2012, from http://www.seaslugforum.net.
• Tan, S. K. & H. P. M. Woo, 2010. A preliminary checklist of the molluscs of Singapore. Raffles Museum of Biodiversity Research, National University of Singapore, Singapore. 78 pp. Uploaded 02 June 2010.
• Tan, S. K. & R. K. H. Yeo, 2010. The intertidal molluscs of Pulau Semakau: preliminary results of “Project Semakau”. Nature in Singapore, 3: 287–296.