Introduction and environmental considerations
Invertebrate classification and relationships
The protists
The poriferans and placozoans
Introduction to the hydrostatic skeleton
The cnidarians
The ctenophores
The platyhelminthes
The mesozoans : possible flatworm relatives
The gnathifera : rotifers, acanthocephalans, and two smaller groups
The nemerteans
The molluscs
The annelids
The arthropods
Two phyla of likely arthropod relatives : tardigrada and onychophora
The nematodes
Four phyla of likely nematode relatives : nematomorpha, priapulida, kinorhyncha, and
loricifera
Three phyla of uncertain affiliation : gastrotricha, chaetognatha, and cyliophora
The โlophophoratesโ (phoronids, brachiopods, bryozoans) and entoprocts
The echinoderms
The hemichordates
The xenoturbellids : deuterostomes at last?
The nonvertebrate chordates
Invertebrate reproduction and development : an overview