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Aquatic Invertebrates

 

Amphipods

An amphipod, Hyalella azteca.
Hyalella azteca.

Class: Crustacea - Crustaceans
Order: Amphipoda - Amphipods
Family: Hyalellidae - Hyalellids

Species found in the Rideau River:
Hyalella azteca

Characteristics of the family:
Members of the Hyalellidae family are small amphipods with relatively short antennas and large eyes. The last segment of the abdomen is entire, which means it is not split or cleft. Most live in marine environments but some of the members live only in freshwater.


Representative species: Hyalella azteca
Description Small bodied, commonly with 2 to 3 teeth (like on a saw rather than in a mouth) on the back at the hind end of the body. Colour is variable with white, green and brown being common, but they can be reddish, bluish or purple. The 2nd leg of the male is much larger and broader than that of the female.
Size 3 to 8 mm (Males are larger than females).
Distribution Found in permanent freshwaters of North and Central America, north to the treeline. Common in the Rideau River.
Habitat Among vegetation in lakes or rivers.
Food Mostly filamentous algae and diatoms, but may eat decaying organic material as well.
Life cycle For up to a week before mating, males carry females by grasping the 2nd segment of the female's body. This is known as precopula. In this way, males assure themselves a female to mate with when she moults and the eggs are laid. The female has large plates on the underneath of her body in which she keeps the eggs. When the young hatch they look like tiny adults. Breeding takes place when water temperatures reach 10°C (about April to October near the Rideau River), with many broods per year.
Interesting facts These amphipods are quite common along the shoreline, but because of their small size they are not usually noticed. They are good swimmers and dart about in the algae.

 

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A Project of the Canadian Museum of Nature
 Images: Ed Hendrycks