part of part of pelvic fin clasper pelvic fin clasper UBERON:0010518 myxopterygium The rod-like extension of the medial portion of the pelvic fin in male Elasmobranchii and Holocephali. Claspers are used as intromittent organs (not in clasping), the grooves on their facing surfaces together forming a tube for the transmission of sperm when the claspers are held together. The anterior proximal opening is called the apopyle, the posterior distal opening the rhipidion. clasper