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Pleopis (formerly Podon) polyphemoides

A marine cladoceran, collected in a 20u net tow sample from Eastern Bay. They feed on dinoflagellates, such as Gymnodinium sanguineum, and on soft-bodied protozoans, invertebrate larvae, and occasionally suck blood out of small copepods and rotifers. They are also reported to graze on diatoms. Their single large eye is capable of forming an image. The animals apparently see their prey and grab it with their claw-like legs

This animal hatches from resting eggs, and can reach high densities when conditions are suitable in the spring and fall. The population consists largely of females for most of the season. They reproduce parthenogenetically, without fertilization, and give birth to small females who are themselves pregnant.  At 20-25C water temperatures, a generation (birth to first birth) lasts 2-3 days. Consequently, populations can increase at rates greater than 10-fold per week when conditions permit, enabling these animals to exploit blooms of their prey organisms.

When conditions are less favorable, a large proportion of males appear in the population. When females mate with males, rather than giving birth to live young, they produce large spherical resting eggs, which fall to sediment as the animal dies. These eggs hatch again when conditions are favorable, starting the population cycle over again.

They frequent the mainstem of the Chesapeake Bay and can reach high densities if conditions are suitable. 

For more information about this species contact Dr. Paul Fofonoff here at SERC, fofonoffp@si.edu.

  Reference: Egloff, David W., Fofonoff, Paul W., and Onbe, Takashi 1997. Reproductive biology of marine cladocerans. Advances in Marine Biology 31: 79-167

Microzooplankton