Euphausiacea
Dana 1852
Taxonomy
| Phylum | Arthropoda |
| Subphylum | Crustacea |
| Class | Malacostraca |
| Superorder | Eucarida |
| Order | Euphausiacea (krill) |
Distinguishing characteristics
- Euphausiids (krill) are holoplanktonic, relatively large crustaceans.
- Most 1 to 2 cm long as adults, but some can reach 6 to 12 cm long.
- Chitinous exoskeleton made up of 3 parts: cephalon (head), thorax and abdomen.
- The first 2 parts are fused into 1 section.
- The head and thoracic body segments often covered by a carapace dorsally and laterally.
- Transparent outer shell.
- Intricate compound eyes.
- 2 antennae.
- Several pairs of thoracic legs, called pereiopods (number varies among genera and species).
- 5 swimming legs, called pleopods.
- Distinguishable by externally visible gills
Distribution
- Occur in all oceans worldwide.
- Most are epipelagic or, pertaining to, or living in the ocean at a depth of between 180 m (600 ft) and 900 m (3000 ft)', and gregarious, forming large social groupings: swarms or schools.
- Size and density of swarms depends on species and region.
- They often dominate the zooplankton over the continental shelf and in regions of high productivity.
- Only one species is abundant in coastal waters of south-east Australia (Nyctiphanes australis), although many other species can be found in oceanic waters and will be occasionally taken over the shelf.
Ecology
- Worldwide this superorder provides food for baleen whales, manta rays, whale sharks, seals and some seabirds.
- Considered keystone species near the bottom of the foodchain as they feed on phytoplankton and zooplankton, and convert these into a form suitable for larger animals.
- Display large daily vertical migrations, therefore providing food for surface predators at night and in deeper waters during the day.
- Filter feeders; front most thoracopods form fine combs that filter water for food particles.
- Mostly omnivorous. Some species are carnivorous, feeding only on small zooplankton and fish larvae.
- Bioluminescent; possess organs (photophores) that emit light. Precise function unknown; potentially for mating, social interaction or orientation.
Additional information
- Commercially fished in southern waters around Japan, in the Southern Ocean and off parts of the Canadian coast.