Euphausiids of the World Ocean, v. 1.1 (August 2015)

Authors:

Edward Brinton, Mark D. Ohman, Annie W. Townsend, Margaret D. Knight and Amy L. Bridgeman

Welcome to the world of euphausiids. Here we summarize information concerning euphausiid taxonomy, morphology, biogeographic distributions, and larval development. We also include some information on euphausiid behavior, mostly in the form of brief movies of swimming, bioluminescence, and schooling. Information is provided for adults of each of the 86 recognized species. Information on larval development is furnished for 70 of these species, although the amount of data available and level of detail differ considerably from one species to the next. For both Adults and Larvae, the sequences in which genera and species are listed are strictly alphabetical. For an explanation of the probable evolutionary progression of euphausiid genera, please see the discussion in Higher Taxa, Order Euphausiacea, Arrangement of Genera concerning patterns of modifications of the thoracic legs from the presumed most primitive (Bentheuphausia ) to the most specialized (Stylocheiron ) genus (sequence of genera).

Beginners may have trouble differentiating euphausiids from other shrimp-like crustaceans, including mysids and pelagic decapods. The Introduction section provides a brief account of distinguishing characters. The Matrix key module will also help here. Launch Matrix key to select the characters and appropriate character states that match the animals that you have. Then click on search to find those taxa that match your selected character states. The % column indicates the percentage agreement with the selected states.

The module Higher Taxa provides diagnoses of the 2 families and 11 genera of euphausiids. Proceed to another taxon using the "next" arrow or, as in all modules, select from the "contents" button at the upper right of the screen.

There are 2 pathways that will permit you to identify adult euphausiids to the species level: Dichotomous key or Matrix key. Explore them both. Dichotomous key presents the user with a sequence of choices. Matrix key does not follow a linear progression, but permits the user to find which taxa match any set of character states that is discernable on the organism. As an alternative to either of these, information on biogeographic distributions can be a useful starting point. To learn which species have been found previously in a particular sector of the ocean, launch Distribution module. Select the "Search" option, then select appropriate map scale from the "map" menu bar above the map, click on the square defining the geographic area of interest, and select "Search >>". To see the geographic distribution of any of the species whose names are listed from your selected region, just click on that name. To compare the distributions of any 2 species, select the "Compare" tab, select the two of interest from the drop-down list to the right, then select "Compare". Note that each of the modules in this expert system has many options and merits the time spent experimenting to learn your way around. You will find context-sensitive help buttons throughout the system.

In addition to the digital Distribution module, each Species card includes a distributional map. Display these maps (and any other illustrations of interest) by selecting the "Media" tab at the top of the species card and clicking on the "distribution" illustration. While these maps lack the versatility of the digital maps found within Distribution module, they provide more detail.

The Species cards are the primary sites of information about each species and contain information on both adults and larvae. The Adults species section includes a morphological description of each species, including comments on distinctive characteristics and notes on horizontal and vertical distributions. The small overview illustration found to the right of the description is only the beginning. Be sure to select the "media" tab at top and examine the numerous line drawings, photomicrographs, and video clips available. A few key references are listed with each species in the "literature" tab, along with other tabs for synonomies and taxonomy. Note that where available, information on juveniles is generally included with the Adults species section.

The Larvae species section can be found below the adult information on the species card and contain Margaret Knight's synthesis of information on the morphology of euphausiid larvae, both published and from her unpublished files. The "development summary" table includes information, where available, on the eggs, nauplii, metanauplius, calyptopis, and furcilia phases of the life history. These tables are also accessible from the "development" tab, as are a few examples of the variations in frequency of different length classes or in frequency of different stages. As authors differ as to the assignment of furcilia in different states of development to discrete "stages," these tables present information on the forms that have been reported previously as well as the correspondence between forms and stages. Note that some species of euphausiids have flexible development pathways; in some environments, they may have a lengthy sequence of furcilia forms, while in others development may proceed through fewer forms. In the furcilia phase, the number of pairs of setose pleopods is designated (") and of non-setose pleopods is designated ('). For example, 3"2' denotes a furcilia with 3 pairs of setose and 2 pairs of non-setose pleopods. Other important characters for staging furcilia include the number of telson spines, with "t" denoting terminal and "pl" denoting posterolateral telson spines (e.g., 5t + 3pl) and the state of the second antenna, whether natatory (endopod unsegmented) or juvenile (endopod segmented).

The Larvae species section includes illustrations of selected stages with some of their distinctive characteristics highlighted with red arrows. For a complete explanation of these characteristics, be sure to read the description of each phase on the together with the detailed illustrations in the "media" tab.

The Glossary module defines and illustrates most of the specialized terminology used in this euphausiid expert system. Use it liberally, as we think it will help you to understand and visualize the morphology and behavior of euphausiids. Glossary entries are hot key-linked to most parts of the system. You can also find uses of terms anywhere in the system with the "Search" command at the upper left of your screen. Select the module in which you wish to search (or "anywhere") at the "search in" prompt. "Advanced search" will report all occurrences of the search term simultaneously, while "Search" will step through the occurrences one at a time.

The Index module lets you display the names of all taxa included in this system, listed aphabetically or in a taxonomic hierarchy.

We hope you will find this system useful and illuminating. Please convey your comments to us (the authors' addresses are in the Contributors section).


Edward Brinton
Mark D. Ohman
Annie W. Townsend
Margaret D. Knight
Amy L. Bridgeman