Open Circulatory System

• Blood is not always inside blood vessels

• Heart pumps blood into a short vessel that opens into the body spaces containing the internal organs

• Blood sloshes over organs and returns eventually to the heart

Open Circulatory System

Mollusks that live in water have gills

• Gills = organs that remove oxygen from the water

• Gills have cilia that move back and forth, making water flow over the gills

Land Snail

Photo credit: NOAA

Aquatic Snails

Photo credits: MSC

Slug

Photo credit: NOAA

Banana Slug

Photo credit: MSC

Nudibranch

Photo credit: MSC

More Nudibranchs

Photo credits: MSC

Bivalves --clams

• http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-clam-vs-world/