This is an entirely arbitrary grouping on my part. There are a number of phyla that are not considered as complex as the arthropods, for example, and I will deal with them here.

Really, when talking about invertebrates in Iowa and the study of them, we need to mention the work of Charles Drewes. He was a professor at Iowa State University who did a lot with invertebrates. Unfortunately, he died suddenly a few years ago, but not before leaving a great web site dealing with Iowa's invertebrates. That web site can be found here:

Dr. Drewes website

By looking at the Illinois list (see the introduction to the biological diversity section), we might get some ideas about the number of species we have here.

Phylum Porifera: We do have freshwater sponges in Iowa. Illinois has 14 species. We probably have a few less. Dr. Drewes had photos on his web site.

Phylum Cnidaria: This group includes the salt water jellyfish and corals. The Illinois list has 10 species of hydra and one species of jellyfish. We do have freshwater jellyfish in Iowa according to Dr. Drewes' web site, and we probably have a smaller number of hydra than does Illinois.

Flatworms, Phylum Platyhelminthes: Illinois lists 400 species. I don't know of an Iowa list.

Phylum Nemertina, Ribbon worms: Illinois lists one species. I do not know if it is found in Iowa as well.

Phylum Nematoda, Round worms: The Illinois list does not give an estimate. I don't know of an Iowa list. There is a huge number of species, and they can be both important pests of crops and important predators of crop pests.

Phylum Nematomorpha, Horsehair worms: The Illinois list has two species. Iowa has at least one. These worms are internal parasites of grasshoppers and crickets which emerge from the insect near water. They look like a hair that can swim.

Phylum Acanthocephala, Spiny-headed worms: The Illinois list has 27 species. I am not aware of any information for Iowa.

Phylum Gastrotricha: The Illinois list has 60 species. I am not aware of any information for Iowa.

Phylum Rotifera: The Illinois list for this group of microscopic animals has an estimate of 150-175 species. I am not aware of any information for Iowa.

Phylum Entoprocta: The Illinois list has one species. I am not aware of any information for Iowa.

Phylum Annelida: The Illinois list has 170 species. The list includes earthworms, leeches, "suction feeding worms", and crayfish worms. I am not aware of any Iowa specific information.

Phylum Tartigrada, Water bears: 13 species for Illinois, I have no information for Iowa.

Phylum Mollusca: The Illinois list has 170 species of snails and 104 species of bivalves--mussels and clams. I have included a treatment of the Iowa snails--50 aquatic species and 134 species of terrestrial snails in subsequent pages. (There is some overlap of aquatic and terrestrial snails). There is a list of mussels of Iowa, and it has 48 species.

Phylum Ecotprocta: Bryozoans: The Illinois list has 9 species. Dr. Drewes has photos of some on his web site. I don't know of any Iowa specific information.

I am not aware of any list of Iowa's crustaceans. However, there is one for Illinois. The list for Illinois includes 207 species, including an estimation of 43 species of water fleas.

Illinois extends much further south than does Iowa, and although much of Illinois is similar to Iowa in habitat, there are areas that are much different. As a result, Illinois probably has more biological diversity than does Iowa. Comparing groups that are known, I would estimate Iowa's numbers of species to be approximately 3/4 to 4/5 the size of those of Illinois. Therefore, Iowa probably has about 150 species of crustaceans.

There are a number of other arthropod groups that I have not really covered yet at all. Some are well known but most are not.

This would include spiders, mites, pseudoscorpions, opiliones (also known as Daddy long-legs), mites, millipedes, and centipedes.

In general, there is not an Iowa list for any of these groups, and there are no good field guides for any of them. The mites are so unknown that there are probably a number of undescribed species in Iowa.

There are 530 species of spiders on the Illinois list.  Iowa probably has between 400 and 500 species of spiders.

There is a group of very small creatures that have three pairs of legs and an organ under their bodies that releases suddenly like a spring, allowing them to jump huge distances on a relative scale. This group is the springtails or collembola.  Historically they have been grouped with the insects although generally they are now not considered to be insects, and are sometimes grouped in their own separate class. The largest of these in Iowa may get to be about 1/8 of an inch long, but most are much smaller. They can be seen with the naked eye but a small hand lens makes it easier.

If you look under the bark on a damp fallen log, or under the log itself you will see them. If you look at the edge of water where duckweed forms thick mats you might see them as well. They will be small black dots that occasionally jump out of view.

Harlow B. Mills was a student at Iowa State in the 1930's and he wrote a master's thesis that latter became a book. The book (from the thesis) was:

Mills, Harlow B., M.S. 1934. The Collembola of Iowa: Collegiate Press, Inc

Mr. Mills listed 132 species from the state of Iowa.

Dr. Kenneth Christiansen from Grinnell College is a world recognized expert on the group.