Acorn barnacle and acorn shell are

vernacular names In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...

for certain types of stalkless

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

s, generally excluding stalked or gooseneck barnacles. As adults they are typically cone-shaped, symmetrical, and attached to rocks or other fixed objects in the ocean. Members of the barnacle order Balanomorpha are often called acorn barnacles. Acorn Barnacles - Flickr - brewbooks

In addition, several species of barnacles are specifically called by the common name "acorn barnacle", including: * ''

Balanus glandula ''Balanus glandula'' (North American Acorn Barnacle, Common Acorn Barnacle) is one of the most common barnacle species on the Pacific coast of North America, distributed from the U.S. state of Alaska to Bahía de San Quintín near San Quintín, ...

'', Common Acorn Barnacle * '' Balanus nubilus'', Giant Acorn Barnacle * '' Chthamalus antennatus'', Acorn Barnacle * '' Megabalanus coccopoma'', Titan Acorn Barnacle * '' Megabalanus tintinnabulum'', Titan Acorn Barnacle * '' Paraconcavus pacificus'', Red-striped Acorn Barnacle * '' Semibalanus balanoides'', Northern Acorn Barnacle

References

{{Animal common name Animal common names