Cercopagis pengoi, or the fishhook waterflea, is a species of planktonic cladoceran crustaceans that is native in the brackish fringes of the Black Sea and the Caspian Sea. In recent decades it has spread as an invasive species to some freshwater waterways and reservoirs of Eastern Europe and to the brackish Baltic Sea. Further it was introduced in ballast water to the Great Lakes of North America and a number of adjacent lakes, and has become a pest classified among the 100 worst invasive species of the world.
Cercopagis pengoi
The Diplostraca or Cladocera, commonly known as water fleas, is a superorder of small, mostly freshwater crustaceans, most of which feed on microscopic chunks of organic matter, though some forms are predatory.
Diplostraca
A cladocera giving birth (100x magnification)
Evadne spinifera, one of very few marine diplostracan species
Ephippia (singular: ephippium) are winter or dry-season eggs of the various species of small crustacean in the order Cladocera (within the Branchiopoda); they are provided with an extra shell layer, which preserves and protects the resting stages inside from harsh environmental conditions until the more favorable times, such as spring, when the reproductive cycle is able to take place once again. Ephippia are part of the back of a mother carrying them until they are fully developed. After molting, the ephippium stays in the water, or in the soil of dried puddles, small ponds, and vernal pools. The resting stages are often called eggs, but are in fact embryos with arrested development. Ephippia can rest for many years before the embryo resumes development upon an appropriate hatching stimulus.
