Idon't have much time! answer quickly! 2 questions:
1. which system of grouping is in figure 18-2, a or b provides information about the evolution of the three animals
2. according to the cladogram in figure 18-2, what two characteristics do crabs and barnacles share that limpets do not?
you in advance

The correct answer is-

1) Cladogram

2) Molted external skeleton and segmentation.

A cladogram can be described as a diagrammatic representation in a  branching treelike form, which is used to depict phylogenetic relationships among different species.

For every divergence point in a cladogram, the two branching lines show descendance, which indicates divergence of species from a common ancestor. Thus, it is a system of grouping of various organisms.

In the given cladogram, the two characteristics that are shared by crabs and barnacles but not by limpets are Molted external skeleton and segmentation.