evolutionary relationships between different phyla of invertebrates?

Answer 1

The following site:
http://whozoo.org/inverts/animalphylo.htm
has a nice phylogenetic tree of the invertebrates as well as a listing of all the known phyla.

Answer 2

It is unlikely that we will ever know with any high
degree of probability what the evolutionary tree of
the invertebrates is. Some of the recent proposals
that have been made, based on molecular research, are radically different from earlier proposed phylogenies. I rather question whether
even the molecular data will answer this question.
There are about as many problems with interpretation of molecular information as there are
with other kinds of data. Also, what a particular
gene does in one organism may be different
from what it does in another, even though it is
considered to be the "same" gene. This sort of
historical question may be inherently unanswerable.