You learn the Find Familiar spell and can cast it without material components. The ability to use and cast this spell replaces your Wild Shape feature. When summoned this way, your familiar is a fey instead of a celestial or fiend. Your familiar stays in the form in which you originally summoned it. You can expend one use of your Wild Shape feature to recast Find Familiar  on your familiar, changing it's form for a number of hours equal to half your druid level (min 1).