arthrostracous

adjective1

1. •
   (rare) Pertaining to the Arthrostraca, an obsolete grouping of crustaceans with segmented thoraxes and abdomens, bearing seven pairs of thoracic legs; included in this group are the isopods and amphipods.

   • [...] and have considered the possibility of their derivation from either the Arthrostracous Crustacea or the tracheate Arachnida. — 1886