Michael Pitts / Giant clam mantle {Tridacna gigas} and siphon, Palau, Micronesia

Georgette Douwma / Kaleidoscopc Incurrent siphon or inhalant siphon of a clam. North Sulawesi, Indonesia. Indo-West Pacific.

Georgette Douwma / Kaleidoscopic image of a clam's siphon. North Sulawesi, Indonesia. Indo-West Pacific.

Gary Bell/ Oceanwide / Giant Clam (Tridacna sp) siphon, Great Barrier Reef, Australia

Jan Hamrsky / Hoverfly larva (Syrphidae), using its breathing siphon to reach atmospheric oxygen, Europe, November, controlled conditions

Jan Hamrsky / Hoverfly larva (Syrphidae), using its breathing siphon to reach atmospheric oxygen, Europe, November, controlled conditions

Jan Hamrsky / Hoverfly larva (Syrphidae), using its breathing siphon to reach atmospheric oxygen, Europe, November, controlled conditions

David Fleetham / Broadclub cuttlefish (Sepia latimanus) with siphon visible Bali, Indonesia.

Linda Pitkin / Giant Clam, siphon (Tridacna sp.) Sangeang, off Sumbawa, Indonesia.

Claudio Contreras / Common octopus (Octopus vulgaris) showing siphon, Puerto Morelos National Park, Caribbean Sea, Mexico, February

Richard Robinson / Close up of gloomy octopus (Octopus tetricus) eye and siphon, North Island, New Zealand. October. Cropped.

D. Parer & E. Parer-Cook / Paper Nautilus (Argonauta nodosa) mouth, siphon and eye, Port Phillip Bay, Victoria, Australia