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Phylum Arthropoda > Subphylum Crustacea > Class Cirripedia
Parasitic barnacle
Thompsonia sp.
Family Thompsoniidae
updated Feb 13

Where seen? These gruesome animals are often seen growing in flower crabs (Portunus pelagicus). Infected crabs are usually encrusted with non-parasitic barnacles and other animals and seaweeds. They usually move weakly and are generally in poor shape.

Features: This barnacle grows through the body of the host crab like a root system. The parasite does not kill the crab but it does affect the crab's reproductive system such that the crab becomes infertile.


The parasitic barnacle eventually produces tiny egg sacs (0.5cm or less) that emerge through the crab's joints.

Changi, Apr 05

Chek Jawa, Oct 08

Tiny egg sacs emerging through the joints.

*Species are difficult to positively identify without examination of internal parts.
On this website, they are grouped by external features for convenience of display.

Parasitic barnacles on Singapore shores

Photos of Parasitic barnacles for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

Links References
  • Lim, S., P. Ng, L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times of Labrador Beach. Division of Biology, School of Science, Nanyang Technological University & Department of Zoology, the National University of Singapore. 160 pp.
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