They may be called known as acanthocephales , thorny-headed worms , or spiny-headed worms . They have an evertable proboscis , armed with spines , which they use to pierce and hold the gut wall of the host . Acanthocephala ( Greek , ' , thorn + , ' , head ) is a phylum of parasitic worms known as acanthocephales , thorny-headed worms , or spiny-headed worms , characterized by the presence of an evertable proboscis , armed with spines , which it uses to pierce and hold the gut wall of its host .