Wednesday, June 12, 2013

Isopods (Phylum Arthropoda: Order Isopoda) of Singapore

Isopods (phylum Arthropoda, subphylum Crustacea, class Malacostraca, order Isopoda) probably has the most diverse appearance among the crustaceans, ranging from flattened and bug-like, to longish and worm-like. Most of the ones seen on land and in shallow water have the former appearance though.

They lack an obvious carapace, or have a very reduced one. With regards to their diet, some species are scavengers or detrital feeders, some are known to feed on algae, and some parasitise other animals, but generally, little is known about the diet of most isopods.

Here are some of the isopods that I have photographed in Singapore:

The Woodlouse (Suborder Oniscidea) is commonly seen in damp areas in parks and forests, such as in the leaf litter or under logs. They have the typical flattened appearance and clearly segmented bodies. Like most terrestrial crustaceans, they have brood pouches on the underside of their bodies to keep the fertilised eggs until they hatch. Woodlice seen in Singapore are seldom more than 1cm long, and most are just a few mm long.

Some woodlice may roll into a ball when disturb, and are often called pillbugs. Generally, woodlice play the important role as decomposers in terrestrial ecosystems, though some species may feed on shoots and young fruits and hence are sometimes considered minor pest in gardens.

The Sea Slater (Ligia sp.) is an isopod commonly seen on seashores, especially rocky areas, moving quickly around and scampering away in a split second when disturbed. They are scavengers, and thus help to keep the shoreline clean as they feed on any dead animal materials on the shore. Like the woodlice, female Sea Slaters also have brood pouches to keep the fertilised eggs until they hatch. Sea Slaters in Singapore are mostly less than 2cm long (head to end of abdomen).

Bopyrid Isopods (family Bopyridae) are parasitic isopods which live in the gill chambers of bigger crustaceans, causing a lump-like swelling. The picture above features a shrimp with a parasitic isopod on one side of its gill chamber, resulting in a big, tumour-like lump. These isopods attached themselves to the gills with strong, hook-like appendages, feeding on the blood from the gills.

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  • Burnie, D. 2001. Animal. London: Dorling Kindersley. 624 pp.
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  • Ng, P. K. L., S. S. L. Lim, L. K. Wang & L. W. H. Tan. 2007. Private lives: An exposé of Singapore's shores. The Raffles Museum of Biodiversity Research, Department of Biological Sciences, National University of Singapore. 212 pp.
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  • World Register of Marine Species. 2012. Retrieved Jun 10, 2013, from

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