Acorn barnacle

Acorn barnacle and acorn shell are vernacular names for certain types of stalkless barnacles, 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.

[1][2] In addition, several species of barnacles are specifically called by the common name "acorn barnacle", including:[3][4][5]