Egg Hatching, Miracidial Morphology, and Pathology of Chimaerohemecidae sp. (Digenea) Infecting Gill of Smooth Butterfly Rays, Gymnura micrura, from Mobile Bay, Gulf of America

While searching for monocotylid (Monogenoidea) and blood fluke infections in smooth butterfly rays captured in Mobile Bay (north-central Gulf of America), we observed hatching blood fluke eggs (Chimaerohemecidae sp.) embedded in the gill epithelium. Eggs presented as large, nearly grossly visible, opaque white or slightly tan, and irregularly shaped oblong masses ∼3 mm in maximum length and having ∼172 eggs per mass. Wet-mounting allowed excision of live eggs, and examination with a compound microscope revealed that each egg had an actively gyrating and ciliated miracidium. Unhatched miracidia began rapidly extending and contracting their bodies, stretching the pliable (non-operculate) eggshell immediately before emerging from the egg, darting away, and swimming rapidly in a seemingly haphazard manner. The resulting 28S sequence (1,537 bp; OQ709103) of Chimaerohemecidae sp. claded with that of other chimaerohemecids and was most similar (87%) to that of another Gulf of America chimaerohemecid, Myliobaticola richardheardi Bullard and Jensen, 2008. The miracidium of Chimaerohemecidae sp. is morphologically unique among fish blood flukes by lacking eyespots and a stylet as well as by having only a single miracidium in each egg. Our pathology results revealed that infection (probably egg hatching) disrupted the overlying gill epithelium and contributed to crater-like lesions but that an inflammatory response and gill epithelial hyperplasia were lacking. This is the first published description of a chimaerohemecid egg and miracidium, the first elasmobranch gill pathology study involving a blood fluke, and the first observation of chimaerohemecid eggs hatching while embedded in the gill epithelium. The present study also contributes some egg and miracidial features that could eventually further diagnose and differentiate the accepted genera and families of fish blood flukes.