Haas' specialty involved the study of land and freshwater snails, as well as research of the family Unionidae (freshwater mussels).
Prominent were freshwater fish (primarily bonytail, Gila elegans, and razorback sucker, Xyrauchen texanus), freshwater mussels (Anodonta dejecta), water birds (particularly American coot, Fulica americana), and marsh plants (cattail, Typha, tule, Scirpus, and reed, Phragmites).
Bitterlings have a remarkable reproduction strategy where parents transfer responsibility for the care of their young to various species of freshwater mussels (Unionidae and Margaritiferidae).
Epioblasma torulosa, species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels