Cumaceans are small crustaceans that are related to crabs and shrimp.  However their anatomy differs enough from crabs and shrimp that experts in crustacean biology have put them in a separate category that also contains isopods (marine pill bugs) and amphipods (beach fleas).  The body consists of a head shield or carapace on which the eye (red in the photograph) is located, a thorax and finally a long narrow abdomen which ends in the forked telson.  Cumaceans range in size from about 1/16th to 1/2 of an inch long.  The individual in the photograph is enlarged around 50X from its original size of 1/16th of an inch.

They are bottom feeders living on or near the surface of a variety of sediments from sand to mud where they feed on suspended detritus or organic films.  They have been found from the intertidal zone to deep ocean where water currents are not strong and in a wide range of salinities, .  They are attracted to the night lights and at certain times of the year are present in large numbers if not eaten by Shinner Perch or Threespine Sticklebacks.