Summary DescriptionAPI English: A photograph of the sea slug Siphopteron quadrispinosum engaged in reciprocal copulation. Caption from source: "The bipartite penises, which are everted as largely translucent structures at the right front of the head (h), are reciprocally inserted into the partner. While the actual penis (p) is inserted into the gonopore (located behind the right parapod), the penile stylets (s) are hypodermically inserted into the foot of the partner. Markings are only shown for the lower animal." Date 26 August 2012 Source Lange R, Gerlach T, Beninde J, Werminghausen J, Reichel V, et al. (2012) Female Fitness Optimum at Intermediate Mating Rates under Traumatic Mating. PLoS ONE 7(8): e43234. doi:10.1371/journal.pone.0043234 Author Lange R, Gerlach T, Beninde J, Werminghausen J, Reichel V, et al.