Euphaciaceos

C O N S E I L INTERNATIONAL P O U R L'EXPLORATION DE L A M E R

Zooplankton
Sheet 134

EUPHAUSIACEA
Adults
(By J. MAUCHLINE)

1971

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Order Euphausiacea

There are only 6 species of euphausiids that reside permanently and breed in the North Atlantic, north of 40" N. These are: Thysanopoda & LL, Meganyctiphanes norvegua (M. SARS), Thysanoessa inermis (KR~YER), longicaudata T.acutifrons HOLT T A ~ R S A Nyctiphanes couchii (BELL), (KR~YER) T. raschii (M. SARS). A further 8 species occur fairly commonly in southern regions of the North Atlantic and are occasionally and caught in more northern areas; these are Bentheuphausia amblyops G. 0 .SARS,lhysanopoda microphthalma G. 0 .SARS, Euphausia krohnii (BRANDT), Thysanozssa gregaria G. 0 .SARS, Nematoscelis megalops G. 0.SARS,Nematobrachion boopis (CALMAN), Stylocheiron elongatum G. 0 .SARS, .longicorne S G. 0 .SARS, .maximum HANSEN, S abbrevMtum G. 0.SARS. These species are all included in the key presented here. S and . Occasional individuals of other species have been recorded in the sea area lying between southern Ireland and 4 N (see MAUCHLINEFISHER, 0 ' & 1969) but these species have not been included in the key.If a species is not identified by the key given here then recourse should be made to the fuller key and to the sources of original descriptions of species given in MAUCHLINEFISHER & (1969). There are two families of the Order Euphausiacea, the first, the Bentheuphausiidae, consisting of only one genus with one species, Bentheuphausia (Fig. 1). amblyops G. 0.SARS 1. The endopodites of the firstand second pairs of pleopods of the male are not modified as copulatory organs and the basipodite of the first pair of pleopods carries 1-6 spines. The endopodite of the maxillule has two joints and the endopodite of the maxilla has three joints. The outer plates of the uropods have a transverse suture. There are no photophores. The eyes are reduced in size and all eight pairs of thoracic legs arewell developed ..................................................................... Family Bentheuphausiidae COLOSI 2. The endopodites of the first and second pairs of pleopods of the male are modified as copulatory organs and the basipodite of the first pair of pleopods has no spines. The endopodites of the maxillule and maxilla have a single joint. The outer plates of the uropods have notransverse suture. Photophores are present. The eyes are well developed and the last or the penultimate and last pair of thoracic legs are rudimentary ...................................................................... Family Euphausiidae HOLT& TATTERSA

KEY TO GENERA OF EUPHAUSIIDAE
1 a. 1 b. 2 a. 2 b. 3 a. 3 b. 4 a.
Thoracic legs nearly uniform in structure................................................................................ 2 5 Thoracic legs unequally developed, one or two of the anterior pairs being elongated .......................................... 3 Eighth pair of thoracic legs rudimentary ................................................................................ Seventh and eighth pairs of thoracic legs rudimentary. Sixth pair similar in appearance to fifth................. Euphausia DANA Seventh pair of thoracic legs of same appearance as sixth, but shorter in length.. ................ Thysanopoda MILNE-EDWARDS 4 Seventh pair of thoracic legs has endopodite of not more than two elongate segments.. ........................................ Sixth and seventh pairs of thoracic legs have exopodites in both sexes. There is a reflected leaflet on the firstsegment of the antennule. One pair of lateral denticles on carapace. ............................................. M8.~anyctiphancsHOLT& TA~TERSALL 4 b. Sixth and seventh pairs of thoracic legs have no exopodites in female. There is a reflected leaflet on the first segment of the antennule. No lateral denticles on the carapace ..................................................................