DiagnosisThese beasts are also known as the spiny lobsters and it's obvious why! Identified by their very spinose ornament, the carapace lacks a rostrum, but is fused to the epistome laterally. The pleon is well developed and they have exteremely powerful mandibles.
OriginThe origin of this group lies a little later than the Astacidea or Dendrobranchiata and is thought to be between 250- 240 million years ago.
Images are found at http://www.unc.edu/depts/oceanweb/lobsters/index.html