76 CRUSTACEA—COPEPODA CHAP. 
are prehensile, but are not so fused. Besides Achtheres there are 
other fresh-water forms, eg. Lernaeopoda salmonea on Salmon, 
and a number of marine genera. It appears that the larvae fix 
themselves to their hosts by means of a long glandular thread, 
which proceeds from the middle of the forehead.’ 
Fam. 13. Choniostomatidae.’—The members of this family 
are all parasitic on other Crustacea. The majority live parasiti- 
cally in the marsupial pouches of female Amphipods, Isopods, 
Mysidae, and Cumacea, e.g. Sphaeronella and Stenochotheres in the 
marsupiaof Gammarids; but Chonio- 
stoma occurs in the branchial cavity 
of Hippolyte, Homocoscelis is common 
in the branchial cavity of Diastylis 
\ and Jphinoe, and Aspidoecia on the 
outside of the body of the Mysid 
Erythrops. The males and females 
live together in the same marsupium, 
but the adult males retain the power 
of roving about, and do not feed so 
much as the females, though their 
mouth -parts are similarly  con- 
structed (Fig. 47). Representatives 
occur all over the world, but the 
majority of species known at pre- 
Fic. 47.—Ventral view of Stenocho- sent are from the North Sea, the 
se Ce aa ge eae most abundant being Stenochotheres 
bet tial nee eqregius, parasitic on the Gammarid 
sen) Metopa bruzelir, Goes. 
The male bears a median glandu- 
lar thread on the forehead by which it attaches itself to the 
females or to the host. Hansen considers that the family is 
most closely allied to the Lernaeopodidae. 
BRANCH II. BRANCHIURA. 
Fam. Argulidae..—We have yet to mention this group of 
fish-parasites, related to the Copepoda, but occupying an isolated 
1 Claus, Zeitschr. wiss. Zool. xi., 1861, p. 287. 
* Hansen, ‘‘ The Choniostomatidae,’’ Copenhagen. 
° Claus, Zeitschr. wiss. Zool. xxv., 1875, p. 217. 
