Physical Description
Introduction
The
euphausiacea is best characterised by its shrimp like appearance with a highly developed
carapace fused with all thoracic segments. To differentiate the euphausiacea
from the decapods (prawns, lobsters, crabs etc.) it can be noted that the carapace
does not extend to the ventral side of the thoracic segments as it does in
decapods. Another difference to be noted is the exposed gills present in
euphausiacea unlike the brachial chamber present in other crustaceans.
Most
of the euphausiacea display some form of bioluminescence to assist in schooling
and mating displays. E.recurva did
display this trait particularly under the microscope otherwise appeared a
transparent yellow/brown colour with females often expressing darker
colouration when holding eggs.
E.recurva is
a smaller member of the euphausiacea with most adults only reaching lengths of
10mm. Individuals reached sexual maturity at approximately 7mm as observed by
individuals carrying eggs at this size.
Methods
Due to the large diversity of these shrimp like
creatures between the true shrimp (decapods), mysid shrimp and krill
(Euphausiacea) identification is often difficult. Due to size and limited
studies on many of these taxa care must be taken in their identification. For
the identification of this species two keys were used to improve accuracy and
attempt to better understand the classification of these animals. The two
classification keys used were Marine Species Identification Portal and Intkey
on crustacean identification. I focused more on the Marine Species Identification Portal
due to a number of technical errors occurring in Intkey.
To
first separate the krill from the decapods, the physical characteristics listed
above were used. At this stage the key required the physical appearance of the
eye, was it darkly pigmented or weakly pigmented followed by the shape, round
or oddly shaped. Following these prompts with a darkly pigmented round eye the
next distinguishing feature involves the shape of the frontal plate which is
the most oral end of the carapace on the dorsal side. The frontal plate of this
species is not truncated and its margins converged to form an acute angled
pointed rostrum. The presence of spines behind the eyes (post ocular) was also
a distinguishing characteristic that was absent in E.recurva.
At this point observations of the abdominal segments were made, to further divide the various taxa the presence or absence of mid dorsal spines was taken into account and the length ratios of the abdominal segments. E.recurva displayed no dorsal spines and a proportionally larger sixth abdominal segment to those surrounding it.
To
identify the remaining species from one another it was required to compare the
lappets. The Lappets are a small process extending dorsally from the first
segment of the antennae.
Results
In the case of this species the lappet was unforked
and displayed a unique recurving leaflet only found of E.recurva.
The marine species identification portal assisted in identifying this species through a thorough identification process. Although this process covered various features there is always the potential for error based on the perception of identifier and diagrams on the identification portal. There is a high diversity of shrimp like crustaceans in the worlds oceans and many that are yet to be discovered, despite their high ecological importance there is still many avenues to be explored in their identification.
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