Here is the underside of a female roly poly. Her head is at the top. You can see her marsupial pouch taking up over half the length of her body. The yellow spot in the center is the opening for entering and exiting the pouch. The white rectangles under the pouch are her gills. As you can see, this one has empty places where more gills could be added. The drier the environment that the isopod lives in, the more gills it will have. 

Giant marine isopod

Holy Moly Roly Poly!!

• Roly Polys are also called pillbugs, potato bugs, sow bugs, and their scientific name isopoda, or isopods.
  

• Isopods are crustaceans not insects. They are closer related to shrimp and lobster than insects.

• Terrestrial isopods breathe through gills. They need moisture in the air to breathe but they can not live under water.

• Isopods are found all over the world except Antarctica.

• The largest isopods are found in the Atlantic ocean. The largest found was 30.5 inches long
  

• Isopods have a marsupial pouch like a kangaroo. Depending on the species, the babies can crawl in and out of their moms pouch for several weeks after birth.
  

• Isopods do not urinate.  Most animals need to convert waste material that is high in ammonia into urea before it can be excreted from the body. Isopods can tolerate ammonia  which can pass directly through their exoskeleton.
  

• No daddy's required. If there are no male isopods around, a female can reproduce by parthenogenesis. 

• Isopods blood is blue. Most animals have hemoglobin in their blood that contains iron and turns red when combined with oxygen. Isopods have copper in their blood that turns blue. 

• Most terrestrial isopods can curl into a ball when threatened. HippPolys have outgrown their ability to do this.

• Isopods can drink water through their butt.

• Pocket Pets are relatively independent and self entertaining, therefore don't require the attention that other small pets do.