Order EUPHAUSIACEA Dana, 1850

Museums

Museum list

Regional Maps

Order EUPHAUSIACEA Dana, 1850

Introduction

The order takes its name from the genus Euphausia and is derived from the Greek eu meaning `good' or `true', and phausia for `shining' or `light emitting'. This refers to the bright photophores typically present on the eyestalk, thoracic appendages and between the pleopods under the abdomen. The common name for the group, `Krill', was first used by Norwegian whalers who applied it to the swarming little fish (krill) which signalled whale feeding grounds.

Euphausiids are exclusively marine, and occur in all the world's oceans, ranging in depth from the surface to 4000 metres. There are 86 known species in 11 genera and two families, the Euphausiidae and the Bentheuphausiidae, although the latter comprises only a single genus and species. Distributions are often wide-ranging—many of the deeper-living species occur circumglobally, whereas the distibutions of those living in waters shallower than 300 metres tend to be more influenced by factors such as current patterns, water temperatures, and salinity.

Euphausiids spend their entire lives in the water column. They are primarily omnivorous filter-feeders with their diet consisting principally of zooplankton, phytoplankton, and suspended detritus they generate by disturbing bottom sediments. They generally disperse for feeding at night, but in the pre-dawn often form dense aggregations which can undergo deep vertical migrations. During the day these aggregations may form narrow or deep layers at varying depths in response to environmental factors such as thermoclines or oxyclines, but like Nyctiphanes australis, they can also form tight balls (Mauchline & Fisher 1969).

Besides being a crucial food source for whales, their high protein content has led to them being harvested commercially as food for aquarium and farm animals. There is also an increasing interest in fishing Euphausia species for direct human consumption, and small fisheries already exist in waters off Japan, Canada, and the Antarctic.

Other important general references on biology and taxonomy of relevance to the Australian fauna include: Tattersall (1936a, 1936b); Boden et al. (1955); Brinton (1975); Mauchline (1980); Baker et al. (1990); and Brinton et al. (1999).

Diagnosis

Carapace covering entire thorax, fused to underlying thoracic segments; single series of prominent exposed feathery gills in form of podobranches attached to exopodites of thoracic limbs; in some genera thoracic limbs all similar in structure with none obviously modified into maxillipeds, but in others (Nematoscelis, Nematobrachion, Stylocheiron, Tessarabrachion, and some Thysanoessa spp.) second and third thoracic endopods (corresponding to maxillipeds) are extremely elongate, and sometimes raptorial, while fourth to eighth endopods are reduced; first maxilla with pseudexopod in most genera (true larval exopod persists only in Pseudeuphausia sinica), second maxilla with relatively small exopod; complex movable photophores typically present at least on abdomen (except in certain bathypelagic species); statocysts absent; no special brooding structures, eggs generally shed free, young hatch as nauplii in the first of a long series of larval stages. (After Schram 1986; Brinton et al. 1999).