Hermit crabs. Male and female hermit crabs (Pagurus pubescens) under water. Hermit crabs (superfamily Paguroidea) do not have their own shell. They have long, soft abdomens which they protected from predators by living inside a salvaged empty seashell. They carry the shell on their back and can retract their whole body into it. Most frequently hermit crabs use the shells of sea snails and the tip of their abdomen is adapted to clasp strongly onto the shell's coiled internal structure (columella).