I talk a lot about mimicry on this site, and I’ve explained why: it’s good evidence for natural selection, poses testable hypotheses, and, not least, provides some amazing examples of the power of natural selection—especially because in many cases of mimicry we can identify the “target of selection”: the optimum phenotype that provides the greatest fitness. And these cases often show that the target is pretty well hit: see many examples here.
Here’s a pretty amazing one I didn’t know about, but was spotted by Matthew Cobb on Twi**er. It’s a cuttlefish that mimics a hermit crab. Or at least that’s what it seems to be doing.
— Niki Hubbard 🐙🌊🦀 (@NikiHubbard) June 12, 2017
Here’s a longer video from National Geographic, clearly showing that the cuttlefish mimics the crab’s shell, its antennae, and its claws. The last minute of this 2-minute video offers the hypotheses (camouflage from prey or prdators) and the situations in which the mollusks do this. But is it learned or in the genes? The video doesn’t tell us.
It’s the Pharaoh Cuttlefish, Sepia pharonis. Wikipedia explains how they change color:
Pharaoh cuttlefish often show a solid color when resting on a solid color background, alternating from a pale white to all dark brown. Additionally, they can show a mottled white and brown color, with a center circle of brown. The mechanism for color is the same in the Pharaoh cuttlefish as it is in other cuttlefish. This colour-changing function is produced by groups of red, yellow, brown, and black pigmented chromatophores above a layer of reflective blue and green tinted iridophores and leucophores, with up to 200 of these specialized pigment cells per square millimeter. These sacs of color are controlled by rings of muscle around the sac. The cuttlefish expands and contracts these muscle rings in order to show different colors.