Freshwater Crustaceans

This is just a quick overview of the extreme basics of collecting freshwater crustaceans. I do not consider myself an expert, and will likely update this as I learn more. For now I just want to gather some information in one place.

Basics

Western Canada's freshwater crustaceans include the following groups: Podocopida (freshwater ostracods), Copepoda (copepods), Cladocera (water fleas), Anostraca (fairy shrimp, ~20 sp.), Notostraca (tadpole shrimp, ~5 sp.), Laevicaudata/Spinicaudata (clam shrimp, 3 sp.), Amphipoda (amphipods, ~10 sp.), Asellidae (freshwater isopods, ~3 sp.), Bathynellacea (bathynellans, ? sp.), Mysida (opossum shrimp, 2 sp.), and Astacoidea (crayfish, 2-4 sp.).

Hand collection of most specimens can be done by scooping them directly into a watertight vial (be sure to label, and take note of habitat), or carefully pipetting them into a vial of water using an eyedropper (the standard 3mL disposable kind found at drugstores works well). Fragile specimens may be damaged by pipetting. Fully grown adults are usually required for identification (but sometimes smaller individuals at a site may be a different species), and often one sex (usually male) is required.

Planktonic groups of crustaceans can easily be collected via nets. Benthic groups such as many ostracods and harpacticoid copepods require other techniques, for example collecting sediment that can then be washed through a sieve.

Many species can be kept in refrigerated water for up to a week; however, to preserve them they should be transferred to ethanol while still alive. 95% ethanol is ideal for DNA work, but makes specimens brittle and difficult to dissect during identification. For this purpose, 70% should be used instead. Alcohol from freshly collected specimens should be discarded and replaced after about 24 hours; this ensures that the tissues reach a sufficient (non-diluted) concentration. Unfortunately, ethanol typically requires a work permit to obtain; isopropanol isn't as good, but can be used as an alternative and is obtainable at most drugstores.

Once specimens are obtained, most must be identified under the microscope, often requiring dissection. Ideally, one should have access to both high-quality dissecting and compound microscopes. Specimens can be deposited on a depression slide. Measurements are often useful and should be taken. Then, while keeping the specimen submerged in alcohol (or ideally glycerin), entomological pins held in a pin vice (or an alternative setup) may be used to coax appendages into view (at the risk of damaging the specimen). Back and top lighting can both be useful for viewing structures.

Ostracods

Ostracod preservation is a special case; for dissection, ideally they should first be killed in 30% alcohol. This relaxes their shells, making them easier to open. Moreover, due to having calcified shells which dissolve over time in alcohol, long-term voucher specimens are usually dried. Many species can be recognized by the shape of their shell; however, for confident identification a shell usually needs to be dissected to observe the appendages hidden inside.

Copepods

There are three groups of freshwater copepods in our area: Calanoida (antennae long, typically reaching body length, body narrows substantially at about halfway), Cyclopoida (antennae short, body narrows), Harpacticoida (antennae very short, body remains about the same width, mostly benthic).

For most copepods, the antennae and dorsal views of abdominal shape, caudal filaments (at the abdomen tip), and caudal rami (the structures to which the filaments are attached) are useful for identification to genus. For reliable identification of calanoid copepods, most require dissection of the 5th leg from an adult male. Males can be recognized by their elbowed right antennae. For cyclopoid copepods, females (having both antennae unbent) are more helpful, and the 4th leg also becomes useful. The freshwater Harpacticoids are poorly studied and only a few species in Canthocamptidae are recorded; in addition, the marine Tigriopus californicus (Harpacticidae) is often found in abundance in splash pools just above the intertidal.

Resources

Ecology and classification of North American freshwater invertebrates, 2e. Thorp & Covich, 2001.
Diversity and distributions of circumpolar fresh- and brackish-water Mysis. Audzijonyte & Väinölä, 2005.

Ostracods

Soft body morphology, dissection and slide-preparation of Ostracoda: a primer. Namiotko et al., 2011.
Field key and methods of collecting freshwater ostracodes in Canada. Delorme, 1967.

Copepods

An introduction and key to the freshwater Calanoid copepods (Crustacea) of British Columbia. Sandercock & Scudder, 1994.
Species identification of the fresh-water Cyclopoid Copepoda of the United States. Pennak, 1963.
An annotated checklist and keys to the species of Copepoda Harpacticoida (Crustacea). Wells, 2007.

Fairy Shrimp

Key to the Anostraca (Fairy Shrimps) of North America. Belk, 1975.
Key to the Anostraca of British Columbia. Grant, n.d.

Publicado el diciembre 29, 2023 08:04 TARDE por shawnb2