296 MARINE INVERTEBRATES 
On the cephalothorax are seven pairs of appendages. The first pair are 
small and lie in front of the mouth ; these and the four following pairs have 
chele, or claws. The sixth pair haveno chele, but at the base havea pecu- 
liar process termed the flabellum. These six pairs of appendages surround 
the mouth, and have bristles at the base which serve as jaws. The sev- 
enth pair of thoracic appendages are broad plates called the operculum, 
which meet and cover the abdominal appendages to a certain extent. 
The abdomen has five pairs of appendages, which are plate-like and re- 
semble the operculum in form and have an upper and an under piece. 
On the posterior surfaces of the abdominal feet are large, leaf-like folds, 
which are the gills. In front of the first pair of thoracic legs is a small 
tuberele supposed to have an olfactory function. Limulus has a blood- 
vascular system (the blood being bluish in color), a nervous and a diges- 
tive system. It walks with the thoracic feet and swims with the abdom- 
inal ones. It enters the sand by pushing in the rounded, anterior end. 
In moulting the carapace opens on the front edge. Limulus is edible, its 
meat being, it is said, as good as that of the lobster. (Plate LXIV.) 
CLASS PANTOPODA (Lang) 
ORDER PYCNOGONIDA 
This order of animals, like Limulus, has no definitely deter- 
mined position in the classification of marine organisms. About 
one hundred and fifty species of Pycnogonida have been described, 
of which thirty are found on our coast and are commonly known 
as sea-spiders. They are found crawling slowly over seaweeds, 
hydroids, and sponges, and appear to be all legs, but, like other 
animals, have a digestive, a circulatory, and a nervous system. 
They are devoid of organs of respiration. The body has a 
cephalothorax, which bears a conical suctorial proboscis on the 
anterior end, and on top a prominence containing four eyes. It 
has three pairs of appendages, two pairs of which are sometimes 
lacking ; then come three free segments and a rudimentary abdo- 
men. There is a pair of short appendages bearing claws (chelz) 
and four pairs of long walking-legs. The walking-legs contain 
a tubular outgrowth of the body, into which the stomach extends. 
The egg-sacs are in the legs, and open at the basal joints. The 
male is provided with an extra pair of legs, for the purpose of 
carrying the eggs after they are deposited by the female. The 
