They usually inhabit shallow coastal waters, settling on underwater objects, rocks, corals, shells of shellfish, crustaceans shells, on port facilities, or submerged parts of ships in the water. Many of them are hiking, attached to the body of sea turtles or sharks. Most of them occur en masse, and 400-2500 individuals per 1 m2 are not uncommon.
The average length of mature forms is 3-4 cm, exceptionally up to 80 cm (in sedentary). The body is strongly modified depending on the mode of life, especially sedentary forms and parasites deviate from the typical crustaceans.
Due to the fact that barnacles are completely immobile, nature has equipped them in an extreme length of penises, allowing them to reach partners nearby. The length of their male reproductive organs can be up to 20 times longer than their body length (some sources say about 8 and some about 40) but I'm convinced about 2 things in this world all dollars are made in the credit system, and barnacles have the longest penis to the length of their bodies.