Euphausia eximia Hansen, 1911
Etymology: Euphausia - brightly shining; eximia - ornate
Eye: The eye is round and large (E. eximia eye & rostrum). The eye diameter : carapace length is about 0.21.
Peduncle of 1st Antenna: The 1st segment has a large, dorsal, forward-directed, comb-like leaflet. The 2nd segment is slightly longer than the 3rd. The dorsal side of the 2nd segment has two prominent, somewhat curved, forward-projected spines, one on the outer edge and one on the inner edge. The 3rd segment has a keel which is acute anteriorly (E. eximia,).
Rostrum: It is long, sharply pointed, reaching the anterior limit of the eyes (E. eximia eye & rostrum). The gastric region is domed, with a small keel at its apex.
Carapace: There are two pairs of lateral carapace denticles (E. eximia carapace denticle).
Abdomen: There are no dorsal spines or specific features (E. eximia).
Length: Adults are large, 15-30 mm.
Petasma: The terminal process is long and almost straight. The distal part is slightly and evenly curved. At the beginning of the curvature is a slender, straight spine, the tip of which does not quite reach the end of the process. The proximal process is bent at the base and the remainder is slender, ending in a flattened plate. Near its distal part the median lobe expands laterally as a broad triangle. The curved lateral process is inserted near this expansion. The setiferous lobe is of regular width but is partly truncate at the end, which carries six or seven setae (E. eximia petasma).
Thelycum: Described by Guglielmo and Costanzo, 1978.
Comments: The large and graceful form and the ornate comblike lappet suggest an eximious or ornate appearance.
ECOLOGY
E. eximia appears to be reproductive in productive northern and southern upwelling zones which are marginal to the anoxic basin (5-20°N) of the eastern tropical Pacific. It is of the same large size and gross appearance as frequently cooccuring E. gibboides . However, E. eximia is not trans-oceanic in its range, being more nearly restricted to low latitude habitats served by coastal and equatorial upwelling.
HORIZONTAL DISTRIBUTION
E. eximia is restricted to the Pacific. The range is in the warmer equatorward parts of the California and Peru Current systems, including the Gulf of California, and extends westward along the equatorial divergence, sometimes to near mid-ocean (E. eximia distribution).
VERTICAL DISTRIBUTION
E. eximia is a vertical migrator between the surface layer and about 300 m.
LARVAE
See the development summary (E. eximia Table) for the stage descriptors and length in stage.
Metanauplius - (1 stage) (E. eximia A)
Carapace:
Shape - The frontal hood is rounded and moderately wide.
Marginal spines - The frontal hood is fringed with small spines. There are three pairs of longer spines interspersed along the anterior margin and there are 3 smaller spines between the inner pair of the long spines.
Dorsal crest - There is a high crest with a pair of relatively short dorsal spines.
Calyptopis - (3 stages) (E. eximia B), (E. eximia C)
Carapace:
Shape - The frontal hood curves in medially. It has oblique lateral margins in C1, in dorsal view, and is curved in around the eyes in C2-C3.
Marginal spines - The frontal hood is fringed with spines.
Postero-dorsal spine - A postero-dorsal spine is present.
Lateral denticles - A pair of denticles is present.
Leg 1 (maxilliped): In C1, as in E. diomedeae , the stout seta on the first segment of the endopod is smaller than the stout seta on the basis. (Euphausia larval maxilliped), (larval maxilliped basis)
Telson:
Shape - The telson is broad. There is less incurve below the lateral spines than in related species, and the lateral spines are a little more distally situated.
Postero-lateral spines - PL2 is longer than PL3.
Furcilia - (6 stages) (E. eximia D), (E. eximia E), (E. eximia F)
A1: The lappet on the first segment of the peduncle may have a small marginal knob or spine in F5 and more than 1, often 3, processes in F6.
Eye: The eyestalk photophore is less high than in related species. The faceted area is somewhat rounded and the pigment develops in 3 zones. (Euphausia larval eye)
Carapace:
Frontal plate / rostrum - It is rectangular in F1 and becomes broadly triangular in late furcilia, a rostral spine is present from F2, it is small in young furcilia.
Marginal spines - The frontal plate is fringed with small spines through F3, they are reduced in number in F4, and there may be a few small spines in F5.
Postero-dorsal spines - A spine is present in F1 only.
Lateral denticles - A pair of denticles is present.
Thoracic legs: There is sequential development without elongate leg (s).
Abdomen:
Mid-dorsal spines - absent
Pleopods: The common developmental pathway is 1' - 1"4' - 5".
Telson:
Postero-lateral spines - PL2 is longer than, or equal to, PL3 in F1-F3.
Lateral spines - There is 1 pair through F3, there may be 2 pairs in F4, and there are almost always 2 pairs in F5-F6.
Comments: Larvae of Euphausia species group 1A (Brinton, 1975), E. brevis, E. diomedeae, E. mutica, E. recurva, E. eximia and E. krohni are very similar. E. americana is undescribed.
The calyptopis stages of E. eximia may be distinguished by fairly large body size, and proportions of the telson. The lateral spines are relatively distal, there is only a moderate incurve below the lateral spines, and the postero-lateral margins are moderately rounded.
In the furcilia stages the shape and proportions of the eye are the most helpful feature in recognizing the species. The faceted area is less high and more rounded with a slightly larger lower portion than in related species. The eyestalk photophore is smaller also, reaching only to about the mid-point of the eye.
Development
(E. eximia Table), development summary for the stage descriptors and length in stage.
Pictures
E. eximia, selected stages
E. eximia A [metanauplius]
E. eximia B [calyptopis 1-2]
E. eximia C [calyptopis 3]
E. eximia D [furcilia 1-2]
E. eximia E [furcilia 3-4]
E. eximia F [furcilia 5-6]
E. eximia G [juvenile]
Euphausia larval eye
Euphausia larval maxilliped [species characters]
larval maxilliped basis [species characters]
key to larval illustrations |
