Alex Mustard / Yellowbelly hamlets (Hypoplectrus aberrans) pair spawning at dusk (artifically backlit). Hamlets are hermaphroditic species. George Town, Grand Cayman, Cayman Islands. Caribbean Sea.

Alex Mustard / Black hamlet (Hypoplectrus nigricans) and Yellowbelly hamlet (Hypoplectrus aberrans) spawning at dusk. As this genus is quite recently evolved hybridization is still possible. Hamlets are one of the...

Hiroya Minakuchi / Nudibranch (Hypselodoris bullockii) pair mating, Borneo, Malaysia

Constantinos Petrinos / Ribbon eel in male blue phase {Rhinomuraena quaesita} Sulawesi, Indonesia - species is hermaphrodite changing sex from male to female; juveniles are black, male is blue underneath , and final female p...

Constantinos Petrinos / Giant clam {Tridacna gigas} biggest bivalve species in world, Sulawesi Indonesia. Hermaphrodite producing both eggs and sperm

Tony Wu / Asian sheepshead wrasse (Semicossyphus reticulatus), two males fighting over territory. Female wrasse in background. Niigata Prefecture, Honshu, Japan. June.

Alex Mustard / Pair of Yellowbelly hamlets (Hypoplectrus aberrans) spawning at dusk. Hamlets are one of the few vertebrate species that are true hermaphrodites, here the fish with the open mouth is acting as a male...

Alex Mustard / Pair of Barred hamlets (Hypoplectrus puella) spawning at dusk . Hamlets are one of the few vertebrate species that are true hermaphrodites, here the fish in the foreground is acting as a male, but thi...

Steve Downer / Pair of Black slugs (Arion ater agg.) mating, showing external sperm transfer, Birmingham, England, UK, October.

Steve Downer / Close up of a pair of Black slugs (Arion ater agg.) mating, showing external sperm transfer, Birmingham, England, UK, October.

Steve Downer / Close up of a pair of Black slugs (Arion ater agg.) mating, showing external sperm transfer, Birmingham, England, UK, October.

Steve Downer / Pair of Black slugs (Arion ater agg.) mating, showing external sperm transfer, Birmingham, England, UK, October.