For the sea slug Chromodoris reticulata the penis is a disposable and replaceable instrument
Like almost all nudibranchs, Chromodoris reticulata (Chromodorididae), is a non-selfing, simultaneously hermaphroditic sea slug. In this species partners perform both the ‘male role’ of donating sperm to a mating partner and the ‘female role’ of receiving sperm from the partner simultaneously during copulation.
What’s unique about this species native to the Indo- Pacific, at least while the reproductive biology of other nudibranchs is studied, is the fact that Chromodoris reticulata is able to autotomize its penis after copulation and regrow another penis to copulate again within a day.
Once copulation has ended, both individuals crawl with their elongated penises remaining outside the body, and then they autotomize and discard them. Behavioral observations revealed that approximately 24 h after the previous copulation C. reticulata is able to copulate reciprocally for at least three more times. This is due to that penis has a spiral structure that is believed plays an important role in the autotomy and replenishment. So, a ‘next penis’ is available after 24 h for a new copulation.
Cool, don’t you think?
Photo credit: ©Benjamin Naden | [Top: Manadao, North Sulawesi, Indonesia, 2011] - [Bottom: Seraya Barat, Bali, Indonesia, 2012]
Edit: sorry, I forgot to upload the second photo.