Reciprocal copulation of <i>Siphopteron quadrispinosum</i>.
2013-02-20T00:27:26Z (GMT) by
<p>The bipartite penises, which are everted as largely translucent structures at the right front of the head (<b>h</b>), are reciprocally inserted into the partner. While the actual penis (<b>p</b>) is inserted into the gonopore (located behind the right parapod), the penile stylets (<b>s</b>) are hypodermically inserted into the foot of the partner. Markings are only shown for the lower animal.</p>