Why do desert insects have long legs?
To keep them away from the hot sand. Most desert animals have long legs, mammals and birds too. Think ostrich ^^
There are several insects referred to as "daddy long legs", but all of them are insects, which are arthropods, which is a group of Ecdysozoa, which are creatures which shed exoskeletons. The star fish is an echinoderm, which is a group of Deuterostomia, which are creatures whose first holes during development are their anuses. So starfish are more closely related to human beings than they are to daddy long legs.