Triangle Barnacle

Triangle barnacles are originally native to the Indian and Pacific oceans, but now have a cosmopolitan distribution. Darwin, in his original description, said the species was "widely distributed and where found seems to be common". He gave the species' range as including New Zealand, Sydney, the island of Java, the East Indian Archipelago, Peru, California, and what he called "West Columbia". Triangle barnacles are also native to the waters around Korea and the south of Japan but its presence in the north Sea of Japan is likely due to human activity. Triangle barnacles are also known from the Persian Gulf and the adjacent Gulf of Oman, around the Indian subcontinent, and along the east coast of Africa. However, all triangle barnacle presence in the Atlantic Ocean is introduced, which was once not believed to be true.

Presence in the Atlantic. Today, triangle barnacles are found in the Atlantic in an area drawn from False Bay, northwest to Rio Grande do Sul, north to North Carolina, and east to the Azores. The species is also abundant in the Mediterranean Sea. The triangle barnacle's invasion started in 1867 in southern Brazil when a species since synonymized with B. trigonus was reported from Florianópolis. In the subsequent decades, triangle barnacles were reported from elsewhere in Brazil and in Madeira, the Azores, Guinea, and the Congolese coast.By 1877, B. …

Barnacles are sessile as adults but have motile larval stages, first the nauplii, and then the cyprids, which do not eat but attach themselves to a substrate and metamorphosed into adults. The adults reproduce year-round, and individuals only a month old may do so as well. A given barnacle may also produce multiple broods each year.

Larvae and metamorphosis. The front half of the nauplii is relatively wide and circular, giving the nauplii a "teardrop"-like appearance. Nauplii have six stages, with distinctive characteristics in each, and their size grows from stage to stage. In the first stage, laboratory-raised specimens measured no more than 240 micrometres (9.4 mils), with some variation; by the third stage they measured 480 micrometres (19 mils), give or take 18 μm (0.71 mils). In the sixth stage the nauplius larvae measured 880 μm (35 mils). The nauplii have spines, horns, and maxillules which help identify them; in the final stage of their development, the nauplii have a pair of compound eyes and the primordia of some cyprid appendages. The subsequent cyprid larvae also have compound eyes. A 1990 study revealed that on average, in 20 °C conditions, it took an average of eleven days for the barnacles to grow from a newborn nauplius to the cyprid stage. …