Whale barnacles passively filter food, using tentacle-like cirri, as the host swims through the water.

The barnacle creates a crown-shaped shell, and in most instances, deeply embeds itself into the skin for stability while riding a fast-moving host.

Chelonibia testudinaria turtle barnacle remains from the Pliocene of Italy seemed to have been associated with right whales (Balaena spp.

), and could represent a transitional phase; the lack of competing barnacle species and the softer skin compared to the turtle carapace may have led to a divergence and a dispersal.

Since whale barnacles are monophyletic (the family contains a common ancestor and all its descendants), this dispersal only successfully occurred once.

[7] In 1825, English zoologist John Edward Gray divided Coronulidae into four subfamilies: Tubicinella, Polylepas, Platylepas, and Astrolepas.

[9] In 1916, biologist Henry Augustus Pilsbry differentiated turtle barnacles from whale barnacles and assigned them to Chelonibiinae and Coronulinae, respectively; he also recognized two forms of Coronulinae, coronulid and platylepadi, based on anatomical differences and host preferences.

C. diadema is typically barrel-shaped, has most of the shell emergent from the skin, and has been measured in the North Pacific to reach 39–50 millimetres (1.5–2.0 in) in height.

[14] Tubicinella is tall and tube-shaped with ridges that may serve to prevent the skin from rejecting the barnacle; it typically exceeds 50 millimetres (2.0 in) in height.

[10] The cirri, tentacle-like feeding structures that extend out of the aperture, are short and thick, probably enabling them to remain more stable while riding a fast-moving host.

After settling, the juvenile barnacles form a ring-shaped structure that firmly grips onto the skin, growing upwards as a cylinder.

In Cryptolepas, this process was observed as taking 1.2 to 1.9 seconds, however the forward and backward strokes can be skipped entirely, and the cirri can simply be extended and quickly coil back up.

Having encountered another barnacle, the pair begin a series of intense cirral movements which was observed in Cryptolepas as lasting around 32 seconds.

[21] On right whales (Eubalaena spp) an endemic species of barnacle, Tubicinella is embedded in patches of roughened, calcified skin called callosities.

[23] However, Xenobalanus exclusively inhabits the most turbulent environments for barnacles on flippers, flukes, and dorsal fins.

Barnacle larvae may reach these sites passively, being deposited naturally by vortexes created by the animal, or may crawl to more suitable locations.

[23] Xenobalanus can more easily grow on sick skin with a weakened immune system, and younger individuals tend to have larger infestations presumably because they are less resistant;[16] further, given it has a stalk, it increases the drag felt by the host and may be considered parasitic in that sense.

[17] A Cryptolepas infection on captive beluga whales (Delphinapterus leucas) elicited an immune response by the skin, and the barnacles were ejected after a few weeks.

Others, the Balaenoptera, are adapted for a flight response, probably evolving an antifouling mechanism in their skin to deter infestations, avoiding unnecessary weight which would hinder speed.