 The diet of the porcupine ray consists mainly of benthic invertebrates and bony fishes , which it digs up from the sea floor . It is aplacental viviparous , in which the developing embryos are nourished by histotroph ( " uterine milk " ) produced by the mother . The porcupine ray has long been valued for its rough and durable skin , which was made into a shagreen leather once used for various utilitarian and ornamental purposes , such as to cover sword hilts and shields . It is caught incidentally by coastal fisheries . Because it must be handled carefully due to its thorns , its commercial significance is limited . Unregulated fishing has led to this species declining in many parts of its range , and thus has been listed as Vulnerable by the International Union for Conservation of Nature ( IUCN ) . 
