Ultrastructure of Male Sexual Apparatus of Scutellonema brachyurum.

Electron micrographs of serial sections show that the male sexual apparatus of Scutellonema brachyurum includes two morphologically identical spicules. Each is composed of a swollen tubular head, crescentic shaft, and leaf-like blade with membranous velum expanded from the central trunk. The spicules are concave and grooved on the ventral side and convex on the dorsal side near the trunk. The trunk is continuous with the shaft and head. Nerve tissue occupies the core of the spicule and includes a dendritic process which gains access to the exterior via a small pore on the lateral side of the spicule tip. Three protractor and two retractor muscles are associated with each spicule. A sensory accessory piece connects with the tip of the gubernaculum and protrudes from the lower side of the opening of the spicular pouch; it protracts and retracts with the muscularized gubernaculum. The gubernaculum varies from bow-shaped in the distal part to boat-shaped in the mid region. A sac exits beneath the accessory piece as a buffer for its movement. A cuticular guiding bar originating from the dorsal wall of the spicular pouch has a tongue. The ventral surface of the tongue is sclerotized to separate the two spicules. It is mobile by muscles of the protractor gubernaculi, retractor gubernaculi, and seductor gubernaculi.