III PODOPLEA——-AMPHARTHRANDRIA 63 
Fam. 3. Peltiidae.'— This is an interesting family, allied to 
the Harpacticidae, and includes species with flattened bodies 
somewhat resembling Isopods, and a similar habit of rolling 
themselves up into balls. No parasitic forms are known, though 
Sunaristes paguri on the French and Scottish coasts is said to 
live commensally with hermit-crabs. 
We have now enumerated the chief families of free-living 
Copepods; the rest are either true parasites or else spend a part 
of their lives as such. A number of the semiparasitic and 
parasitic Copepods can be placed in the tribe Ampharthrandria 
owing to the characters of their antennae; but it must be 
remembered that many parasitic forms have given up using 
the antennae as clasping organs; however, the sexual differences 
in the antennae, and the fact that many of the. species which 
have lost the prehensile antennae in the male have near relations 
which preserve it, enable us to proceed with some certainty. 
The adoption of this classification necessitates our separating 
many families which superficially may seem to resemble one 
another, e.g. the semiparasitic families Lichomolgidae and Ascidi- 
colidae, and the Dichelestiidae from the other fish-parasites; it 
also necessitates our treating the presence of a sucking mouth as 
of secondary importance. This characteristic must certainly, how- 
ever, have been acquired more than once in the history of the 
Copepods, for instance in the Asterocheridae and in the fish- 
parasites, while it sometimes happens that genera belonging to 
a typically Siphonostomatous group possess a gnathostome, or 
biting mouth, ey. Ratania among the Asterocheridae. Again, it 
is impossible even if we use the character of the mouth as a 
criterion to place together all the true parasites on fishes in one 
natural group, because the Bomolochidae and Chondracanthidae, 
which are otherwise closely similar to the rest of the fish-para- 
sites, possess no siphon. It seems plain, therefore, that the 
parasitic habit has been acquired several times separately by 
diverging stocks of free-swimming Copepods, and that it has 
resulted in the formation of convergent structures. 
Fam. 4. Monstrillidae.—These are closely related to the 
Harpacticidae. The members of this curious family are parasitic 
during larval life and actively free-swimming when adult. There 
1 Claus, Copepodenstudien, 1. Heft, Vienna, 1889. 
2 Malaquin, Arch. Zool. Exp. (8), ix., 1901, p. 81. 
