Kleptoplasty is the behavior of taking chloroplasts from a food source and incorporating them into the consumer’s cells. The root word klepto- comes from the Greek word for thief. Organisms capable of kleptoplasty typically eat algae or aquatic plants and “steal” the undigested chloroplasts. These chloroplasts can continue to function and provide energy for their new host via photosynthesis.

Some species of single-celled eukaryotes are kleptoplastic. They ingest phytoplankton cells and incorporate their chloroplasts.

The only multicellular animals capable of kleptoplasty are a group of sea slugs called the saccoglossans (SF Fig. 2.3). They eat algae and incorporate the stolen chloroplasts into the tissues of their digestive tract. Sacoglossans have been referred to as “leaves that crawl” and “solar-powered sea slugs.”