Balanus amphitrite (Darwin, 1854)

Striped barnacle

Phylum Arthropoda
Subphylum Crustacea
Class Maxillopoda
Subclass Cirripedia
Order Thoracica
Family Balanidae

Description
Balanus amphitrite is a small, conical, sessile barnacle (to about 1.5 cm diameter). Color is whitish with purple or brown longitudinal stripes. Surface of test plates are longitudinally ribbed. The interlocking tergum and scutum, the paired structures which cover the animal inside are as pictured below.
A similar species, Balanus reticulatus Utinomi, is also an introduced species and commonly occurs with B. amphitrite. It also has longitudinal purple or brown stripes, but these stripes are intersected by horizontal grooves, giving the surface of the test plates a rough reticulated striation, unlike B. amphitrite. It can also be distinguished by examination of the tergum and scutum pictured below. Note the more sharply pointed apex of the tergum and the elongated and narrower tergum spur of B. reticulatus.
Habitat
Very common in the intertidal fouling communities of harbors and protected embayments. The live attached to any available hard surface, including rocks, pier pilings, ship hull, oyster shells, and mangrove roots.
Distribution
Hawaiian Islands
Throughout the main Hawaiian Islands
Native Range
Southwestern Pacific and Indian Ocean
Present Distribution
World-wide in warm and temperate seas
Mechanism of Introduction
Unintentional, as fouling on ships hulls
Impact
Barnacles are a serious fouling problem on ship bottoms, buoys,
and pilings. The ecological impact of this barnacle in Hawaii is unstudied.
Ecology
Feeding
Barnacles have specialized paired appendages, called cirri, that they use as a scoop net, reaching out into the water and extracting food particles. When they cirri are drawn back, food is scraped off into the mouth.
Reproduction
These barnacles are hermaphrodites, but cross-fertilization occurs in dense populations. In such cases, males deposit sperm directly into the mantle cavity of adjacent functional females via a long tube. Fertilized eggs are brooded in the mantle cavity, and it may be several months before the free-swimming planktonic larvae are released.
Remarks
This now widespread barnacle of southern hemisphere origins was first collected in 1902 in Honolulu Harbor. Edmondson (1933, as Balanus amphitrite hawaiiensis) noted that it was very common in Pearl Harbor on piling and shore rocks. Both B. amphitrite and B. reticulatus are well established in Hawaii and have been widely reported by many authors throughout the main Islands.
References
Edmondson, C.H. 1933. Reef and Shore Fauna of Hawaii. B.P. Bishop Mus. Spec. Pub. 22.