Ligia oceanica (Linnaeus 1767)

... I'm a little tired of the rambling pre-amble, so I'm limiting it to one paragraph and the taxonomy. As such, on with the show:

Eukaryota ...has nuclear membrane, various cell organelles...
  Animalia... is an animal...
    Eumetazoa...isn't a sponge... My continuing apologies to poriferophiles...
      Bilateralia... enjoys only one line of symmetry...
        Nephrozoa... depending on phylogeny followed, isn't an acoelomorph flatworm...
          Protostomia... cell fate in embryo is fixed (in most taxa)...
            Ecdysozoa... sheds skin... not unique to the group, but it's in the name...
              Arthropoda...has a jointed exoskeleton, or is descended from something with one...
                Crustacea... is related to crabs, lobsters, etc...
                  Malacostraca... is more closely related to crabs than, say, triops...
                    Eumalacostraca... is more closely related to crabs than mantis shrimp...
                      Peracarida... isn't a crab. Or a lobster. Or a shrimp.
                        Isopoda... is related to woodlice.
                          Oniscidea... is a woodlouse...
                            Diplocheta... isn't a traditional woodlouse...
                              Ligiidae... is a member of one of the various groups occasionally known as 'slaters'

Ligia oceanica

(Linnaeus 1767)

...is a sea-slater. Otherwise known as this: 

  
Widely distributed across the north Atlantic (and attached seas) coasts, this is a semi-marine woodlouse, rarely found any distance from the shore. It munches on various algaes (particularly bladder-wrack, apparently), detritus and microscopic organisms at night, and hides under stones and in crevices during the day.

It's also the UK's largest woodlouse, reaching an inch or so in length.