One characteristic of many lamprey but not of hagfishes is

Today, hagfishes and lampreys are recognized as separate clades, primarily because lampreys are true vertebrates, whereas hagfishes are not. A defining feature is the lack of paired lateral appendages (fins). Some of the earliest jawless fishes were the ostracoderms (which translates to “shell-skin”).

Explanation:

Hope this helps. :-) I explained it in the answer.

answer///multiple alleles;

you know they are heterozygous for a trait because they have it as jj or jj.