Animals - Freshwater Ecology: Concepts and Environmental Applications - page 153

9 Animals
Invertebrates
Phylum Porifera
Phylum Cnidaria
Phyla Platyhelminthes and Nemertea
Phylum Gastrotricha
Phylum Rotifera
Phylum Nematode
Phylum Nematomorpha
Phylum Mollusca
Phylum Annelida
Phylum Bryozoa
Phylum Tardigrada
Phylum Arthropoda
Phylum Chordata, Subphylum Vertebrata
Fishes
Tetrapods
Summary
Questions for Thought
This chapter discusses animals, some of the most fascinating organisms
found in aquatic habitats because of their diversity and behavior. Animals
provide an important indication of the health of freshwater ecosystems be-
cause they integrate stresses and sensitive species are generally not found
in polluted habitats (Palmer et al., 1997; Covich et al., 1999). Food webs
are a major pathway of energy flow through ecosystems and generally are
dominated by animals. I have already discussed the economic importance
of commercial and sports fisheries (Chapter 1). This chapter considers each
group of organisms approximately in order of evolutionary origins.
INVERTEBRATES
Phylum Porifera
Sponges often are thought of as marine animals but can be abundant
in freshwaters. There are about 25 species of freshwater sponges in North
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