126 Wisconsin Academy of Sciences, Arts, and Letters. 
as well as the bryozoan Plumatella polymorpha. Elodea is used 
by Physa sayii, Bythinia tentaculata and Planorbis parvus among 
snails, and by Anax junius, Enallagma, and other insects. The 
Potamogeton leaves serve as a resting place or foraging ground 
for many mollusks and associated animals. Vallisneria, with its 
long, narrow leaves, is a favorite resort of Amnicola and young 
Lymnaea and Planorbis. 
But over and above all the filamentous algae are the great forag¬ 
ing grounds of both mollusks and associated animals. Algae, in 
many places, cover all upright plants like a huge blanket (hence 
often called blanket algae) and among them many animals occur 
in great abundance. No less than 19 higher groups of animals 
have representatives that live among the tangled masses of Clado- 
phora. Planaria maculata, leaches of several species, Glossiphonia 
fusca, stagnalis, complanata, nepheloidea, Dina fervida, and Oli- 
gochaete worms, Stylaria, are at times very abundant; minute 
Cladocera of several species are common; the Amphipod, Hyalella 
knickerhockeri, is the most abundant animal and with this is asso¬ 
ciated the Isopod, Asellus intermedins; among Ephemerids, Caenis 
is common; the nymphs of Corixa, Belostoma, Notonecta, and Plea 
striola are more or less abundant, with adults of Plea and Ranatra 
fusca; Trichoptera larvae, including Agraylea, Hydropsyche, 
Oecetis, Leptocella, Phryganea, Polycentropidae, and a few Helico- 
psyche, are common or abundant; Chironomids, next to Hyalella, 
are the most abundant, their larvae and pupae occurring in count¬ 
less numbers in the mass of algae; Coleoptera include Bidessus 
affinis and B. flavicollis, as well as the larvae of Dytiscids and 
Dascyllidae; the mites (Acarina) are the best represented as re¬ 
gards genera, of which eleven have been identified, including 
Limnesia, Hydrachna (common), Tayas, Piona (not common), 
Hygrobates, Lehertia porosa, Torrenticola, Limnesiopsis, Eylais, 
Unionicola, and Arrhenurus (rare). 
Nearly all aquatic mollusks frequent algal communities. By¬ 
thinia, young Amnicola, Valvata, and Planorbis, especially the 
smaller species, browse among the stringy filaments. As already 
noted in Oneida Lake (Baker 1918, p. 158) some species live in a 
plant habitat when young and later migrate to a different kind of 
a habitat. Pleurocera acuta when young is found in algae but 
later migrates to the boulder or gravel shores, where algal food 
may be gleaned from rocks. Lymnaea winnehagoensis also lives 
in algae when young and later occupies a sand, gravel or boulder 
