Weird phylogenetic tree I am required to create a phylogenetic tree(s) of my genes of interest and am currently blasting (tblastn) my genes of interest from S. mediterranea against model systems before expanding my search.
Problem I get something like the attached which does not look like right. What am I doing wrong? I'm aligning via MUSCLE, and running Maximum Likliehood Protein models and consequentially, using the correct model (JTT, for instance). 
Greatly appreciate any help in advance.
Anyway the chances are this is gene duplication. It will be a housekeeping type gene or else histone that sort of thing. You simply map the different genes onto the various metazoan classes. In your case nematodes and arthropods are basal metazoan, so their is correct given the clade they form part of all all representatives is that gene.

There is nothing weird you just need to read the deep phylogeneticists work like Tom Caveliar-Smith and Sandy Balfour, possibly Blair-Hedges

There are alot of eukaryotes prior to the invertebrates, just look at the Cambrian explosion