This key covers invertebrates that live on or in the rivers and streams of North Dakota. These are the phyla that we have come across in four years of sampling. The clams and snails are in the phylum Mollusca. The insects and crustaceans are in the phylum Arthropoda. There are three phyla that look like worms, the Platyhelimenthes, Nematomorpha, and Annelida. We've also collected a few freshwater sponges which are in the phylum Porifera.
Key to the Phylum
Click on the description that most fits what you are trying to identify. This will take you to a page that has photos of several different groups. If you find what you are looking for, click on the link and/or description accompanying that picture and it will take you to the phylum page for that group. We begin with four choices.
The Arthropods - Most of the larval (Fig. 1-3) and adult (Fig. 4-6) stages of the arthropods have legs (Fig 2, 4, & 5). If legs are not present they exhibit some type of head region (Fig. 1). They have paired mandibles, although may be hidden (Fig. 3). May have a bivalved carapace (Fig.6)
The Worms – The body appears to be elongated, soft, and wormlike (Fig. 7-9). The body of the leeches and flatworms appears to be flat (Fig. 7 & 8). The body of the oligochaetes and nematodes is more of a cylindrical shape (Fig. 9).
Molluscs - Note the appearance of a shell (Fig. 10-13), which covers the body of the mollusk (Fig. 14). The body includes a fleshy mantle (white arrow) and a muscular foot (black arrow) which is used for locomotion.
Porifera - Fresh water sponges have no visible structures other than a mass of cells (Fig. 15).