376 
PHYLUM ARTHROPODA. 
body consists of a vaulted cephalothorax shaped like a 
horseshoe, and an almost hexagonal abdomen ending in a 
long spine. 
Burrowing in the sand, Zému/us arches its 
body at the joint between cephalothorax and abdomen, and 
pushes forward with legs and spine. 
It may also walk 
about under water, and even rise a little from the bottom. 
Fic. 199.—Lémudlus or King-crab. 
ch., Chelicerz ; of., operculum ; 
@., anus. 
It is a hardy animal, able to 
survive exposure on the shore, 
or even some freshening of 
the water. Its food consists 
chiefly of worms. 
The King-crab is interesting in 
its structure and habits and also 
because it is the only living repre- 
sentative of an old race, 
The hard, horseshoe - shaped, 
chitinous cephalothoracic shield is 
vaulted, but the internal cavity is 
much smaller than one would at 
first sight suppose ; the well-defined 
abdomen shows some hint of being _ 
divisible into meso-and meta-soma; 
the long sharp spine is (like the 
scorpion’s sting) a post-anal telson. 
On the concave under-surface of 
the cephalothorax there are six 
(or seven) pairs of limbs, as in 
spiders and scorpions— 
(t) A little pair of  three- 
jointed chelicerze in front 
of and bent towards the 
mouth. 
(2) A pair of pedipalps lateral 
to the mouth. 
(3-6) Four pairs of walking 
legs, the bases of which 
surround the mouth, and 
help in mastication. Be- 
hind these, still on the cephalothorax, there is a pair of small 
appendages called chilaria, 
Then follows on the abdomen a double ‘‘ operculum” with the 
genital apertures on its posterior surface, 
Under the operculum lie five pairs of flat plates bearing remark- 
able respiratory organs (‘‘gill-books”). 
These appendages 
show hints of the exopodite and endopodite structure character- 
istic of Crustaceans. 
Each ‘‘ gill-book” looks like a much-plaited gill, or like a book with 
