section_path: Biodiversity/Invertebrates/Arthropods
section_name: Arthropods
paragraph_text: Arthropods
  
  Five species of krill, small free-swimming crustaceans, have been found in the Southern Ocean. The Antarctic krill (Euphausia superba) is one of the most abundant animal species on earth, with a biomass of around 500 million tonnes. Each individual is 6 centimetres (2.4 in) long and weighs over 1 gram (0.035 oz). The swarms that form can stretch for kilometres, with up to 30,000 individuals per 1 cubic metre (35 cu ft), turning the water red. Swarms usually remain in deep water during the day, ascending during the night to feed on plankton. Many larger animals depend on krill for their own survival. During the winter when food is scarce, adult Antarctic krill can revert to a smaller juvenile stage, using their own body as nutrition.
  
  Many benthic crustaceans have a non-seasonal breeding cycle, and some raise their young in a brood pouch. Glyptonotus antarcticus is an unusually large benthic isopod, reaching 20 centimetres (8 in) in length weighing 70 grams (2.47 oz). Amphipods are abundant in soft sediments, eating a range of items, from algae to other animals. The amphipods are highly diverse with more than 600 recognized species found south of the Antarctic Convergence and there are indications that many undescribed species remain. Among these are several "giants", such as the iconic epimeriids that are up to 8 cm (3.1 in) long.
  
  Slow moving sea spiders are common, sometimes growing as large as a human hand. They feed on the corals, sponges, and bryozoans that litter the seabed.