Morphology and Host-Parasite Relationships of Crithidia flexonema (Trypanosomatidae) in the Hindgut and Malpighian Tubules of Gerris odontogaster (Hemiptera: Gerridae)

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Abstract
Crithidia flexonema was found in the hindgut and Malpighian tubules of Gerris odontogaster, often in mixed infections with the flagellate Blastocrithidia gerridis. The flagellates were of the choanomastigote configuration typical of the genus Crithidia. Ultrastructurally, the flagellates were typical of Trypanosomatidae with a mitochondria with well developed cristae but also with a prominent contractile vacuole and associated spongiome. In the hindgut, the flagellates attached to the whole surface area of the cuticular intima of the rectum and anal tube, though attachment was more intense around the rectal gland cells than to the rest of the rectal wall. Attachment occurred by flagellar hemidesmosomes to the cuticle and by macular desmosomes between adjacent flagella. In the Malpighian tubules, flagellates were found in the lumen either attached to microvilli or free, and intracellularly either within membrane-bound vacuoles or within the cytoplasm of the host epithelium. Attachment to the brush border in the tubules occurred by interdigitation of flagella between microvilli. In addition, there was evidence that a junctional complex might be involved in the attachment to microvilli in the Malpighian tubules.