Nudibranchs are hermaphrodites, that is they are both male and female at the same time. When a pair of nudbranchs mate each fertilises the other and both lay eggs. They live quite short lives, perhaps from 3 months to a year. They genrally live solitary lives but may spend several hours mating.
Left - Risbeckia tryoni showing "trailing behaviour" before mating. Centre - Hypselodoris Benneti mating. Right - various nudibranch eggs, the pink ones belong to as Spanish Dancer, the others are unidentified.


Flatworms, Pseudobiceros fulgor mating


Wobbegongs give birth to live pups. The one pictures left has a large white mark on the shoulder. The skin in this area has been completely removed exposing the underlying muscle. This is believed to be a wound inflicted during mating where the male would have used his teeth to hang on to the female.


In cephalopods the genders are separate and reproduction is sexual. Males produce sperm in packets known as spermatophores.These pass along a groove in a specialised arm with reduced number of suckers. The arm places the spermatophore into the female mantle cavity where it explodes. The sperm then swim to the ovary. Eggs are laid with a high yolk content, so the young are well formed before hatching.