• Spines cover the majority of the outer margin of the caudal ramus
• Caudal ramus less than five times as long as wide (10)
• 12 segments in the first antennae
• Fifth leg has one distinct segment (10)
• Length width ratio of terminal endopod segment on leg 4 typically (Mean +/- Std. Dev): 3.18 +/- 0.234 (11)
• Last three segments of antenna with a finely serrated hyaline membrane; difficult to view if antenna not at the correct angle

The preferred taxonomic name may now be Eucyclops pectinifer for North American specimens. Eucyclops agilis was determined to be invalid and E. serrulatus (considered by some to be a synonym of E. agilis) was redescribed with its range covering Europe, Russia and North Africa (11).

E. agilis is common across North America and has been found in arctic ponds (2), the Finger Lakes (3) and Minnesota (5).

This species is found in the shallow littoral zone in the summer and the deeper profoundal zone during the fall in Minnesota Lakes (6).

E. agilis consumes mostly diatoms and large filamentous algae (4).
E. agilis may enter the brood pouches of Daphnia and prey upon the eggs, causing increased egg mortality (9).

This species reproduces sexually, allowing for early colonization before parthenogenetic species (8). As with all cyclopoids, E. agilis overwinters as an immature copepodite stage in the water column or sediments; enabling the population to out-compete, Cladocera in the early summer (7).

Macrocyclops albidis, a larger cyclopoid copepod, preys on E. agilis (4).

Daphnia pulex can suppress the population growth of E. agilis due to food competition (1).

E. agilis occurs in oxygenated waters and usually ascends into the thermocline when seasonal stratification causes anoxic conditions in lower waters (5).

E. agilis utilizes the dispersal mechanisms of wind and flooding to rapidly colonize new areas in (8).

(1) PARKER, R.A. 1961. Competition Between Eucyclops agilis and Daphnia pulex . Limnol. Oceanogr.. 6: 299-301.

(2) DODSON, S.L. 1975. Predation Rates of Zooplankton in Arctic Ponds. Limnology and Oceanography. 20: 426-433.

(3) HALL, D.J., AND G.G. WATERMAN,. 1967. Plankton of the Finger Lakes. Limnology and Oceanography. 12: 542-544.

(4) FRYER, G. 1957. The Food of Some Freshwater Cyclopoid Copepods and its Ecological Significance. The Journal of Animal Ecology. 26: 263-286.

(5) TINSON, S., AND J. LAYBOURN-PARRY. 1985. The behavioural responses and tolerance of freshwater benthic cyclopoid copepods to hypoxia and anoxia. Hydrobiologia. 127: 257-263.

(6) COLE, G.A. 1955. An ecological study of the microbenthic fauna of two Minnesota lakes. American Midland Naturalist. 53: 213-230.

(7) HANN, B.J., AND L. ZRUM. 1997. Littoral microcrustaceans (Cladocera, Copepoda) in a prairie coastal wetland: seasonal abundance and community structure. Hydrobiologia. 357: 37 - 52

(8)CÁCERES, C.E.,AND D.A. SOLUK. 2002. Blowing in the wind: a field test of overland dispersal and colonization by aquatic invertebrates. Oecologia. 131: 402 - 408.

(9) HANAZATO, T., AND S.I. DODSON. 1995. Morphological defenses of Daphnia against copepod predation on eggs. Archiv fur Hydrobiologie. 133: 49-59.

(10) HUDSON , P. L., L.T. LESKO, J.W. REID, AND M.A. CHRISCINSKE.  2003.  Cyclopoid copepods of the Laurentian Great Lakes.  Ann Arbor , MI : Great Lakes Science Center Home Page.
  http://www.glsc.usgs.gov/greatlakescopepods/Key.php?GROUP=Cyclopoid

(11) ALEKSEEV, V., H.J. DUMONT, J. PENSAERT, D. BARIBWEGURE, AND J.R. VANFLETEREN. 2006. A redescription of Eucyclops serrulatus (Fischer, 1851) (Crustacea: Copepoda: Cyclopoida) and some related taxa, with a phylogeny of the E. serrulatus-group. Zoologica Scripta 35: 123-147.

 Cyclopoid1.mov - Cyclopoid swimming pattern (682 KB)

• Eucyclops agilis: Information from the Great Lakes Science Center, USGS