Mating. The male octopus (foreground) sees the female and pounces on her. He mounts her and inserts his ligula into her mantle cavity. The male stretches his mantle dramatically, presumably to help pump the spermatophore to his ligula. The male removes his ligula and departs.
From: Wood, J.B., E. Kenchington, and R.K. O'Dor. 1998. Reproduction and embryonic development time of Bathypolypus arcticus
, a deep-sea octopod (Cephalopoda
). Malacologia, 39(1-2): 11-19.
Online abstract: http://invertebrates.si.edu/cephs/wko98/wko98.html
To see other cephalopod videos: http://collections.si.edu/search/results.htm?fq=online_media_type%3A%22Video+recordings%22&q=&fq=tax_class:%22Cephalopoda%22