pteropod

Pteropods are a group of small, free-swimming pelagic molluscs that live in the open ocean. Traditionally, pteropods are divided into two lineages: Thecosomata (sea butterflies with aragonite shells) and Gymnosomata (sea angels, shell-less and often predatory). All pteropods are holoplanktonic, spending their entire life cycle in the upper ocean.

Anatomy and form: The name derives from wing and foot. They swim with two wing-like extensions of the foot called parapodia. Thecosomata have transparent aragonite shells; Gymnosomata lack shells.

Distribution and ecology: Pteropods occur worldwide, from polar to tropical regions, mainly in the epipelagic zone. They feed on phytoplankton and microzooplankton and are prey for larger zooplankton, fish, and seabirds. Gymnosomata are active predators of other pteropods and small zooplankton. Through grazing and fecal pellets, they contribute to carbon cycling and can influence nutrient dynamics in surface waters.

Impact and threats: Pteropods play a role in marine food webs as both consumers and prey. Their shells, particularly in Thecosomata, are vulnerable to ocean acidification, making pteropods useful indicators of changing ocean chemistry. Warming and shifts in circulation can alter their distribution and abundance, with potential effects on upper-ocean ecosystems. The fossil record of pteropods extends back to the Cretaceous and provides valuable information for paleoceanography.