Sperm characters in the Hemiuridae (Digenea): first data on Aphanurus stossichii (Aphanurinae) and Ectenurus lepidus (Dinurinae).

The present work provides the first ultrastructural analysis of spermatozoa of two digeneans (Aphanurus stossichii (Monticelli, 1891) and Ectenurus lepidus Looss, 1907) belonging to the unexplored subfamilies of the Hemiuridae, namely, the Aphanurinae and the Dinurinae. In March 2019, these hemiurids were collected respectively from the digestive tract of the bogue Boops boops (Teleostei, Sparidae) and the Atlantic horse mackerel Trachurus trachurus (Teleostei, Carangidae) captured in the coastal zone of the Mediterranean Sea, off La Chebba (Tunisia). The ultrastructural study reveals that both spermatozoa exhibit the Bakhoum et al.'s type II of the digenean sperm cells characterized by the presence of two 9+'1' axonemes, an external ornamentation of the plasma membrane not associated with cortical microtubules and located in the anterior part of the spermatozoon, a single bundle of cortical microtubules, the maximum number of cortical microtubules located in a middle part of the sperm cell, and one mitochondrion. Moreover, they share several ultrastructural features with the studied spermatozoa of Hemiuridae such as the presence of two axonemes with the 9+'1' trepaxonematan pattern, a reduced number of parallel cortical microtubules organized into one field with their maximum number located in the median (A. stossichii) or posterior (E. lepidus) part of the spermatozoon, an external ornamentation of the plasma membrane in the anterior part of the spermatozoon, one mitochondrion, a nucleus, and a small amount of glycogen granules. However, the two studied hemiurids could be distinguished by the morphology of the anterior and posterior spermatozoon extremities and the presence of mitochondrial matrix granules in A. stossichii.