I would like to draw your attention to the review on the evolution of “nuclear hormone receptors in parasitic helminths” by Wenjie Wu and Philip LoVerde published in the Journal for Molecular Cell Endocrinology in 2011.
It gives an overview on how nuclear receptors (NR) evolved in platyhelminths and nematodes. By searching for a cited accession number (a.e. AY395038 , which is the Schistosoma mansoni SmTRα receptor) on ParaSite you can easily find the respective gene and visualise the evolutionary relationships in the Ortholog/GeneTree section.
(SmTRα – the red rectangle marks the duplication event, the red highlighting the queried gene)