Copyright © 1997 Province of British Columbia
Published by the Resources Inventory Committee
Introduction
Calanoid copepods are small crustaceans, 1-5 mm in length, commonly found as part of the free-living zooplankton in freshwater lakes and ponds (Williamson 1991). The monitoring of species change in calanoids can detect environmental changes, such as that resulting from acidification or toxification (Marmorek & Korman 1993). Calanoids are an essential part of the aquatic food chain, and important as both predators and prey (Pennak 1989).
Calanoids are recognized by the position of the body articulation, which is after the last metasomal (or thoracic) segment, and before the urosome (Fig. 1). They usually have an elongated body, long 1st antennae, and well-developed 5th legs, which are used in copulation. These and other characteristics separate them from the other fresh-water copepod groups, the cyclopoids and harpacticoids (Wilson 1959, Williamson 1991). The many variations in the appearance of the calanoid body are illustrated in Huys and Boxshall (1991).
This key was prepared to simplify the process of identification of the thirty species of calanoids we have found in British Columbia, as opposed to the 100 or more species covered in other North American keys (Wilson 1959, Pennak 1989). This key is a part of a larger work on "The Freshwater Calanoid Copepods of British Columbia" (Unpub. MS, by G.A. Sandercock and G.G.E. Scudder).
The species included in the checklist (p. 4) and key (p. 6) of B.C. freshwater calanoids are based on previously published data, and our unpublished records. The latter includes the B.C. records of the late Mildred S. Wilson (MSW, in litt.). The nomenclature used follows Dussart and Defaye (1983). Table 1 (p. 4) lists the B.C. freshwater calanoid species under their usual habitat type, based on our unpublished records. Habitat notes for these species are also found in Wilson (1959), based on their North American distributions.
The major features of the morphology of the male calanoid copepod are given (Figs. 1a, 1b, 2a, 2b), and the female is illustrated for comparison (Figs. 1c, 1d, 2c, 2d). Male calanoids are recognized by having a geniculate right 1st antenna and a non-geniculate left 1st antenna (Fig. 1a), relatively large asymmetric 5th legs (Fig. 2c), and a 5-segmented urosome (Fig. 1b). Females are recognized by having both 1st antennae non-geniculate (Fig. 1c), the 5th legs are relatively small and symmetric (Fig. 2e). The female urosome has 2 or 4 segments, with the enlarged genital segment formed from the fusion of two segments (Figs. 1c, 1d). A female may be ovigerous, carrying eggs in two egg sacs (Fig. 1c) (Wilson 1959, Williamson 1991).
In the lateral view of the whole animal (Figs. 1b, 1d, 7b), the mouthparts and swimming legs 1-4 are represented diagramatically (mouthparts redrawn after Vanderploeg & Paffenhöffer 1985; legs 1-4 redrawn after Sars 1903, and Einsele 1989).
The key provided is for male calanoids only. Wilson (1959) included a key to North American female calanoids, but the taxonomic characteristics are less definitive for females than for males. Pennak (1989) suggested that calanoid females can only be identified to species tentatively, when associated with a known male.
Most of the male key characters are located on the 1st antennae (Table 2, Figs. 3a, 3c) and the 5th legs (Figs. 2a, 2b). Users should be aware that accurate species identification in most cases will involve dissection of parts, slide making and viewing with a compound microscope.