show Abstracthide AbstractBlastocladiomycota, early diverging zoosporic (flagellated) lineages of fungi, are vastly understudied. This phylum includes the genus Coelomomyces which consists of more than eighty fungal species that are obligate parasites of arthropods. Coelomomyces lack a complete asexual life cycle, instead surviving through an obligate heteroecious alternation of generations life cycle. Despite their global distribution and interesting life cycle, little is known about Coelomomyces species. To begin to address this, we analyzed transcriptomes from across host-associated life stages including infection of larva and excised mature sporangia from the mosquito, Anopheles quadrimaculatus. We identified differentially expressed genes and over-enriched GO terms both across and within life stages and used these to make hypotheses about C. lativittatus biology. Generally, we found the C. lativittatus transcriptome to be a complex and dynamic expression landscape; GO terms related to metabolism and transport processes were over-enriched during infection and terms related to dispersal were over-enriched during sporulation. The C. lativittatus transcriptomes reported here are a valuable resource and may be leveraged toward furthering understanding of the biology of these and other early diverging fungal lineages. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Coelomomyces lativittatus developmental stages