While no animal is completely invulnerable, many species on Earth possess tough, rigid shells that provide significant protection against unexpected threats. Several armoured animals can withstand ...

Argonauts are distantly related to a hard-shelled cephalopod called nautiluses, leading scientists to question whether shared genetic information may lead to similar shell formation.

Sometimes when a new shell turns up, hermit crabs will form a line, biggest to smallest, to see which animal fits the new shell. The next smallest will take that crab’s hand-me-down home, and so on.

Octopus tetricus turns a darker shade when it needs to intimidate competitors. Peter Godfrey-Smith/PLOS One "It is very hard to know about the intentions of an animal like this," Godfrey-Smith said.

As hard parts, such as bones or shells, are more likely to preserve than soft-bodied organisms, the snapshot of prehistoric life that we get from fossils can be quite biased. It’s also not usually ...