National Geographic on Instagram: "Video by @joelsartore I A lesser blue crab waves his antenna around not to say hello but to sense the world around him @gulfspecimenaquarium. Those little arms do a lot of work: first, they’re often covered in chemoreceptors, allowing the crab to "sniff" the water. The antenna also have a variety of rheoreceptors, which detect movement of surrounding waters, while the base of antennae in some crabs has a sac-like structure that may be involved in detecting soun