Euphausiacea
Characters used in identification of larvae

The most important morphological character used to identify larvae in their nauplius-metanauplius to calyptopis phases is the gross lateral profile of the carapace which may be sloping or angled.
Eu table 5
Extended legend table 5[/textfile][/l]
In the metanauplius stage, the armature of the [l][m]Glossary[/m][r]Frontal margin[/r]frontal margin becomes a diagnostic character (Eu table 5). It may be present without spinules (e.g.Euphausia frigida 3), with sparse (e.g.Euphausia crystallorophias 2) or dense spinules (e.g.Euphausia frigida 2), or with long bristles. These spinules and bristles may be equal-subequal or variable in size. In some species the spinules extend over the entire carapace margin (e.g.Euphausia longirostris 1).
Eu table 6
Extended legend table 6[/textfile][/l]

In the metanauplius stage and calyptopis phase, the degree of development of the distinct [l][m]Glossary[/m][r]Lateral lobes[/r]lateral lobes on the carapace is also taxonomically important (Eu table 6). These lobes may be virtually undeveloped with the carapace being constricted in the posterior half (e.g.Euphausia frigida 3), be barely developed or be well developed with the carapace broadened in the posterior half (Euphausia triacantha , Euphausia longirostris 1).

At the furcilia phase a frontal plate, which originates from the metanaupliar frontal lobes, develops into a number of shapes, ranging from quadrate to pointed and triangular (Table 7). Apically, the rostrum may appear as a rostral spine (III:Euphausia triacantha 1) or denticle (III:Euphausia superba 3), or it may be absent altogether (I:Euphausia crystallorophias 4).
Eu table 7
Extended legend table 7[/textfile][/l]
Certain larval stages of several [l][m]Glossary[/m][r]species[/r]species have a dorsal organ which may appear as a low crest (Euphausia crystallorophias 3), or otherwise as an abrupt, conical prominence on the carapace (Euphausia triacantha 1, Euphausia longirostris 1 and Euphausia longirostris 2). In other species or developmental stages, this dorsal organ is not apparent.

The posterior margin of the carapace is also of taxonomic value because there is an acute projection which is present in the larvae of Euphausia longirostris, Euphausia hanseni, Euphausia spinifera and Euphausia triacantha (characterised by their strong posterodorsal spines in adults), but absent from the larvae of Thysanoessa, Nematoscelis and the Euphausia group containing Euphausia crystallorophias, Euphausia frigida, Euphausia superba and Euphausiavallentini. This projection may reach up to or beyond the posterior edge of the first abdominal somite.

Abdominal somites are important in the identification of furciliae. On the first somite, lateral tergal wings may be absent or present (Euphausia longirostris 2) or connected dorsally with a collar (Euphausia vallentini 3).
Eu table 8
Extended legend table 8[/textfile][/l]
Most larval euphausiids do not have posterodorsal [l][m]Glossary[/m][r]Spines[/r]spines on the abdominal somites. However, Euphausia longirostris, Euphausia hanseni, Euphausia triacantha and Euphausia spinifera acquire these spines at the furcilia phase.

When the telson becomes separate in the calyptopis 3 stage, euphausiids inhabiting the southern temperate and the Antarctic waters may be distinguished at the generic level according to the position of lateral telsonic spinules. These appear in the proximal half of the telson in Thysanoessa species, in the middle in Nematoscelis species, and in the distal part of the telson in species of Euphausia.

Larval euphausiid eyes may be either rounded (RND in Eu table 7) or bilobed (2-LBD in Eu table 7), the latter being characteristic for advanced furcilia stages of Thysanoessa and Nematoscelis.

The pattern of thoracopod development, which are characteristic for particular stages, provides additional information useful for identification. When developing, thoracopods undergo the following states (Menshenina, 1990): (1) a protuberance; (2) a bifurcated bud; (3) an elongated, unsegmented endopod and a bud-like exopod; (4) a number of endopod segments lower than the definitive one (5); (5) endopod fully segmented but straight or slightly bent; (6) thoracopod of definitive form with a long bent endopod. Thus, for example, the expression T3-2 means that the third thoracic leg is an unsegmented biramous limb while T4>=2 indicates that the second thoracic leg of the animal is least a bifurcated bud.