Crustacea and Arthropod Relationships

Compared to other arthropods, crustaceans are characterized by an unparalleled disparity of body plans. Traditionally, the specialization of arthropod segments and appendages into distinct body regions has served as a convenient basis for higher classification; however, many relationships within the phylum Arthropoda still remain controversial.

Can Crustacea even be considered a monophyletic group?
If so, then which are their closest relatives within the Arthropoda?

The answers to questions...