Bumblebees are important pollinators of wild plants and crops, and their population declines in the recent years can have detrimental effects on both. One of the causes of bumblebee declines is the harmful effects of parasitic organisms such as Crithidia and Lotmaria (Kinetoplastida). We present here data on choanomastigote features of Crithidia bombi Gorbunov, 1987 from the intestine of bumblebees Bombus pascuorum. The ultrastructure of C. bombi choanomastigotes is similar to that of the other insect-infecting trypanosomatids. The features of choanomastigotes of C. bombi are a comparatively thick glycocalyx layer and a slit-like lateral channel of the flagellar pocket. We paid special attention to the cytoskeletal elements of flagellar pocket and its lateral slit, and revealed their connection to the cryptocytostome, found two sets of microtubules homologous to cytopharyngeal bands of bodonids and three microtubular singlets supporting a slit. Expanded TEM observations add new data to the understanding of transformation of a free choanomastigote to the haptomorph.