A male Giraffe has the longest tail because it is 8 feet long and the female Giraffe tail is 7 feet long. The males tail touches the ground almost probably about by 3 feet.
There are many folkloristic legends about it; however the longest animal, living and ever lived, is said to be the ribbon worm Lineus longissimus, reaching more than 60 metres of lenght.
It's called...
It is a ribbon worm and it can grow up to (0.20 in) to over 30 metres (98 ft) long but there are reports that these worms grew over 50 m or 60 m long which is way longer than a basket ball court.