Cirripedia. A Strange Story: from Ducks to Barnacles

Abstract

The name of this subclass of Phylum Arthropoda, from the Latin Cirrus, comes from the particular conformation of the multiarticulated bifid appendages, present in number of six pairs on the thorax of the individuals, which, when projected externally to the carapace, resemble to a lock of curls. These marine invertebrates have a deeply modified morphology if compared to the typical scheme of the crustaceans and of the arthropods in general, for instance, the characteristic segmentation of the body does not appear. Many of them have an exoskeleton formed by calcareous plates, easily fossilizable. The paleontological classification is based on internal and external structures. The ancestral barnacles have appeared from the lower Paleozoic. The balanomorph barnacles were called with the popular name of Acorns of the sea, following strange translations in which our invertebrates were associated with buds or fruits similar to palm dates or acorns of various plants and colors. The first printed illustration of living specimens is due to Rondelet (1555), while what is generally considered the oldest figure of a fossil barnacle with a complete crown is that expressed by Baier (1708). Within the Cirripedia, in the Family Lepadidae, the species have the body formed by plates supported by a peduncle through which they attach themselves to the substrate, usually floating objects, for example, tree trunks or keels of ships. During the Middle Ages, due to this characteristic, they gave credence to the theory that the Lepadidae underwent a singular metamorphosis, starting from their initial status of arboreal fruit up to the status of flying aerial vertebrates, originating sea ducks or geese.