Paramoera walkeri

Like all amphipods, P. walkeri are sexually dimorphic:[3] the males may grow up to 21.7 millimetres (0.85 in); females, 22.8 millimetres (0.90 in). Newborns are approximately 2.5 millimetres (0.098 in). Males mature after 14–15 months, at about 50% their final size.[4] Juvenile P. walkeri are more sensitive to hydrocarbons, such as from oil spills, than older specimens.[5]

P. walkeri live in the benthic zone of the Southern Ocean, all around Antarctica, down to a depth of 310 metres (1,020 ft).[2] During the early winter, P. walkeri migrate upward to the ice, and many congregate around patches of algae,[6] in such abundance that they nearly cover the underside of the sea ice sheets.[7] They are also found in the sublittoral zone, and the bottom level of other shallow locations around the Antarctic coast.[8]

As omnivores, they eat phytoplankton, cryophilic flora, and Diphyllobothrium tapeworms, among other organisms, under the top level of ice. During the summer, their metabolism increases by 80% compared to winter levels.[9] Predators include Trematomus borchgrevinki, T. newnesii, T. bernacchii, Notothenia corriiceps neglecta, and Adélie penguins.[4]

During a female's second (occasionally third) winter, she releases pheromones, picked up by a male's antennae, signaling that readiness to mate.[4] The male then clings on to the female until she molts. The male releases its sperm into the female's marsupium, and the female releases up to 200 eggs.[3][7] When the sea water becomes diluted, the eggs may swell up, to keep the total salinity around the embryos constant. They develop for four-and-a-half months, then hatch in the marsupium. The brooding young remain there for up to a month.[7][2][3]

This species was discovered by Thomas Roscoe Rede Stebbing in 1878, named Atylus antarcticus in 1903, and described as Atylus walkeri in 1906.[10][1][11] It was named after Alfred O. Walker, a fellow of the Linnean Society.[10]