Animals with long, skinny bodies are often called “worms,” but there many kinds of worms—even in the ocean. Annelids (segmented worms) include garden earthworms, their ocean relatives come colors, shapes, and sizes. Some so small that they live between grains sand, while others can be longer than a human eat fish! Marine worms essential to food web, as both predators prey. They help create home...

We show that the proof of Luna’s conjecture about the classification of general wonderful G-varieties can be reduced to the analysis of finitely many families of primitive cases. We work out all primitive cases arising with any classical group G. Luna’s conjecture states that, for any semisimple complex algebraic group G, wonderful G-varieties are classified by spherical systems of G ([12]). Th...

Let G be a connected semisimple group over C, whose simple components have type A or D. We prove that wonderful G-varieties are classified by means of combinatorial objects called spherical systems. This is a generalization of a known result of Luna for groups of type A; thanks to another result of Luna, this implies also the classification of all spherical G-varieties for the groups G we are c...