What is Sea slug, the first animal that can photosynthesise?

Elysia chlorotica is a rare sea slug that blurs the line between plant and animal. Leaf-like and green, it drifts slowly underwater but behaves like a typical animal. Feeding on algae early in life, the slug preserves chloroplasts obtained from it instead of digesting them. Chloroplasts continue functioning independently in the slug, allowing energy production using sunlight through kleptoplasty.