I'm trying to create a cladogram, and I'm not sure if I have it correct. I was given the Taxa Hydrozoa, Bivalvia, Nematoda, Mandibulata, Echinoidea, Squamata and Mammalia and organize them with six branches. I know that Squamata and Mammalia are a sister group. They are also deuterostomes along with Echinoidea. Nematoda and Mandibulata are a sister group, and they are protostomes. But do Hydrozoa and Bivalvia go together? Even though Bivalvia is a protostome and Hydrozoa isn't? I can't find common characteristics between them.

I figured it out... Hydrozoa should be an outgroup, and the protostomes and deuterostomes should be grouped on separate branches.