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Phylum Arthropoda > Subphylum Crustacea > Class Cirripedia
Acorn barnacle
Balanus sp.*
Family Balanidae
updated Oct 2016

Where seen? This small rather pointy barnacle is commonly seen on many of our rocky shores and other hard surfaces in the sea such as jetty pilings, sea walls. Usually, many are crowded together in lower portions and shaded crevices where it is wetter. Unlike the hardier star barnacles (Euraphia sp.) which are found higher up where it is drier.

Features: To about 1 cm across, conical outer shell made up of several wall plates.
While many settle on walls and hard surfaces, some species of acorn barnacles settle on living crabs. Some may also settle on living snails such as the Olive whelk (Nassarius olivaceus). One snail may have more than one of these barnacles on its shell, which are quite large compared to the shell!

On a rock.
Chek Jawa, Jan 05

Tuas, May 05

Acorn barnacles on a wall.

Changi, Jul 09
On a living flower crab.

East Coast, Aug 09
On a living Purple climber crab.

Acorn barnacles on a living snail.

Changi, Aug 05

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

Acorn barnacles on Singapore shores

Photos of Acorn barnacles for free download from wildsingapore flickr

Distribution in Singapore on this wildsingapore flickr map

Sentosa, Jun 15
Photo shared by Marcus Ng on flickr.

East Coast Park, Jul 16 on a sea fan.
Photo shared by Loh Kok Sheng on his blog.

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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