The shell is flexible and covered in a black leathery skin - hence the name leatherback.

BBC: New law to protect Puerto Rico leatherback turtles

While it does sell travel services under the traditional price-disclosed model, the Name Your Own Price service allows customers (that are flexible on the date and time of travel and the choice of supplier) the option to bid for hotel stays and air tickets.

FORBES: How About A New Business Model for Priceline?