LIMULOIDEA
Lim`u*loi"de*a, n. pl. Etym: [NL. See Limulus, and -oid.] (Zoöl.)
Definition: An order of Merostomata, including among living animals the
genus Limulus, with various allied fossil genera, mostly of the
Carboniferous period. Called also Xiphosura.
Note: There are six pairs of leglike organs, surrounding the mouth,
most of which terminate in claws; those of the first pair (probably
mandibles) are the smallest; the others have the basal joints
thickened and spinose, to serve as jaws, while the terminal joints
serve as legs. This group is intermediate, in some characteristics,
between crustaceans and certain arachnids (scorpions), but the
respiration is by means of lamellate gills borne upon the five
posterior abdominal appendages, which are flat and united in pairs by
their inner edges, and are protected by the lidlike anterior pair,
which also bear the genital orifices.
Source: Webster’s Unabridged Dictionary 1913 Edition