I crocheted two mermaid tails for my granddaughter. One is an open concept with one flap over the other and the second tail is a closed, wherein you slide yourself inside.

Specialized Ruby/Selle Italia Flow
1991 Specialized Sirrus, steel frame
Dahon Eco C7
Surly Long Haul Trucker/Terry Fly RS
Trident TWIG Recumbent