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...

Alex Mustard / Butter hamlet (Hypoplectrus unicolor) pair spawning at dusk, George Town, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Stephen Dalton / Edible snails (Helix pomatia) pair prior to mating, UK

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...

Ingo Arndt / Leopard slug (Limax maximus) mating pair following each other shortly before mating. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs, Sw...

Ingo Arndt / Leopard slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs, Switzerland

Ingo Arndt / Leopard slug (Limax maximus) climbing and eating at the same time a rope of mucus after mating. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male...

Ingo Arndt / Leopard slug (Limax maximus) climbing and eating at the same time a rope of mucus after mating. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male...

Ingo Arndt / Leopard slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs.Switzerland. Sequence...

Ingo Arndt / Leopard slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs.Switzerland. Sequence...

Ingo Arndt / Leopard slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs.Switzerland. Sequence...

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.

Ingo Arndt / Leopard slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites and can be seen here transferring sperm to one another through their male organs.Switzerland. Sequence...

Tony Wu / Nudibranchs (Hypselodoris bullocki) mating, Lembeh Strait, North Sulawesi, Indonesia.

Pascal Kobeh / Nudibranchs (Nembrotha lineolata) mating, they are hermaphodites but need another individual for reproduction, Sulu Sea, Philippines

Pascal Kobeh / Nudibranchs (Nembrotha lineolata) mating, they are hermaphodites buty need another individual for reproduction, Sulu Sea, Philippines

Pascal Kobeh / Anna's nudibranchs (Chromodoris annae) two looking about to mate, Sulu Sea, Philippines

Alex Mustard / Pair of Barred hamlets (Hypoplectrus puella) spawning at dusk. This species is hermaphrodite. Wreck of the Oro Verde, Grand Cayman, Cayman Islands. Caribbean Sea.

Alex Mustard / Black hamlets (Hypoplectrus nigricans) spawning, backlit to make the eggs visible. Oro Verde Wreck, Grand Cayman, Cayman Islands. Caribbean Sea, January.

Alex Mustard / High magnification of reproductive apparatus of pair of Lined nembrotha nudibranchs (Nembrotha lineolata) mating. Anilao, Batangas, Luzon, Philippines. Verde Island Passages, Tropical West Pacific Oce...

Alex Hyde / Great Grey / Leopard Slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites, and can be seen here transferring sperm to one another through their male organs. Derby...

Alex Hyde / Great Grey / Leopard Slug (Limax maximus) mating, hanging from a rope of mucus. These slugs are hermaphrodites, and can be seen here transferring sperm to one another through their male organs. Photo...

Alex Mustard / Yellowbelly hamlet (Hypoplectrus aberrans) pair spawning at dusk with the fish in the foreground acting as male which may be a Shy/yellowbelly hamlet hybrid, George Town, Grand Cayman, Cayman Islands,...

Alex Mustard / Butter hamlet (Hypoplectrus unicolor) pair spawning at dusk, George Town, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Alex Mustard / Butter hamlet (Hypoplectrus unicolor) pair spawning at dusk, George Town, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Alex Mustard / Indigo hamlets (Hypoplectrus indigo) pair spawning at dusk, George Town, Grand Cayman, Cayman Islands, British West Indies, Caribbean Sea.

Alex Mustard / Shy hamlet (Hypoplectrus guttavarius) pair 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 this p...

Sue Daly / Nudibranchs (Polycera faeroensis) mating. Channel Islands, UK, June.

Juergen Freund / Nudibranchs (Nembrotha kubaryana) mating. Lembeh Strait, North Sulawesi, Indonesia

Juergen Freund / Nudibranchs (Risbecia Tryoni) mating. Lembeh Strait, North Sulawesi, Indonesia.

Juergen Freund / Nembrotha nudibranch (Nembrotha yonowae) pair mating. Misool, Raja Ampat, West Papua, Indonesia.

Dave Bevan / Keeled slug {Limax sp} pair mating, Wales, UK

Robin Chittenden / Earthworm (Lumbricus terrestris) pair mating in grass, Norfolk, UK

PREMAPHOTOS / Slugs caressing each other in courtship {Trichotoxon sp} Kenya

Robin Chittenden / Earthworm pair (Lumbricus terrestris) mating. England, UK, Europe Hermaphrodites

David Fleetham / Redlip parrotfish (Scarus rubroviolaceus) in initial female phase, defacating sand after grinding up coral polyps and digesting the algae within them, Hawaii, Pacific Ocean.

David Fleetham / Ember parrotfish (Scarus rubroviolaceus) in terminal supermale phase, feeding on algae from coral, Hawaii, Pacific Ocean.

David Hall / Two Indigo hamlets (Hypoplectrus indigo) mating, they are simultaneous hermaphrodites, the individual acting as a male is wrapping around his partner, inducing her to release her eggs, Belize, Caribbe...

David Hall / Two Indigo hamlets (Hypoplectrus indigo) mating, they are simultaneous hermaphrodites, the individual acting as a male is wrapping around his partner, inducing her to release her eggs, Belize, Caribbe...

Tony Wu / Two mature male Asian sheepshead wrasses (Semicossyphus reticulatus) fighting over territory during breeding season. Mature males take on a whitish coloration, when approaching females and during terr...