Figure 23.29: Crustacean Diversity (A) This decapod crustacean is a “Sally Lightfoot” crab from the Galápagos. (B) This pillbug, a terrestrial isopod, can roll into a tight ball when threatened. (C) Minute copepods such as this one are an important link in aquatic food chains. (D) Tadpole shrimp are branchiopods, not to be confused with the decapod crustaceans commonly called shrimp, or with the brachiopods seen in Figure 23.15. (E) Barnacles are sessile, attaching to a substrate by their muscular stalks and feeding with retractable feeding appendages (the delicate, tentacle-like structures seen here).