Facts on Thatched Barnacles

Classification

• Thatched barnacles belong to the same subphylum, Crustacea, as lobsters, crabs and prawns. Crustaceans in turn are members of the diverse Arthropod phylum. Barnacles are in fact more closely related to insects than the mollusks they superficially resemble.

Physical Characteristics

• Thatched barnacle shells have subdued colors, coming in shades of white, gray and occasionally brown. Older individuals are often darker than younger ones. The shells consist of six plates. The species' common name derives from the prominent ribs on the plates, which give the shells the look of a thatched roof. This is a relatively large species, growing to a little more than 2 inches in diameter. If the barnacles are crowded, their shells extend vertically and develop a tower-like appearance.

Feeding

• Barnacles filter tiny microorganisms out of the water. When underwater, they open their shells and extend cirri, appendages that trap passing food items and transfer them to the barnacle's mouth. When the tide retreats barnacles close their shells to prevent dehydration.

Life Cycle

• The familiar shelled adult form is just one stage in the barnacle life cycle. After mating with nearby barnacles, made possible through their very long genitals, the hermaphrodite thatched barnacles retain the eggs in their shells until hatching. After hatching, the free-swimming barnacle larvae are released into the water. The larvae join the zooplankton and undergo several transformations before the final larval stage. At this stage, the juvenile barnacle settles on a rock, where it transforms into the sessile adult form. Barnacles continue to grow in the adult form, molting periodically.

Relationship with Humans

• Thatched barnacles do not appear to be under serious threat from human activities. Barnacles are not harvested as a food source, although it appears that they featured in the diets of native peoples in the past. Other activities, however, might have a negative impact on the barnacles. Like all shelled sea creatures, barnacles are vulnerable to the effects of ocean acidification, as the seas absorb increasing amounts of carbon, and to water pollution.