Spider crabs are a group of marine crustaceans known for their long, spindly legs and rounded bodies ~ often covered in algae and debris for camouflage. Found in oceans around the world ~ including Australian waters ~ they are slow moving scavengers that play an important role in the ecosystem by cleaning up the seafloor. One of the most spectacular natural events involving spider crabs is their mass migration and aggregation for moulting, where thousands gather in shallow waters ~ a rare and mesmerising sight. Despite their somewhat alien appearance, spider crabs are gentle and ecologically important creatures of the sea.