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.

a. by using fur or clothes to trap heat energy near the body