Ultrastructure of mature spermatozoa of a minute featherwing beetle from Sri Lanka (Coleoptera, Ptiliidae: Bambara).

The fine structure of the mature spermatozoa of the feather-wing beetle (Coleoptera: Bambara new species no. 2) is described. Mature spermatozoa are extremely large in proportion to the size of the beetle. Under a light microscope a distinct head, midbody, and tail region can be seen with external coils in both the head and tail regions. Although the beetles were collected and preserved for skeletal anatomical study and not for histological preservation, the substructure comprising the spermatozoa was sufficiently well-preserved for their uniqueness to be appreciated. Observations with an electron microscope show that the axoneme is not contained in the tail region but is threaded through the head coils and then tightly wrapped around the midbody, terminating at the end of the midbody region. Sections through the midbody reveal three distinct layers: an inner electron dense core, a middle very elaborate crystalline Jattice-like matrix, and an outer axonemal wrapping. The structures observed in the head and tail regions appear to be modifications of those present in the midbody region. The possible functional significance of these unusual structures is discussed.