Below I have provided images of Cercopagis pengoi from the Baltic Sea, adjacent to the city of St. Petersburg, and from Lake Ontario. Samples from the Baltic Sea were collected during 1997. The species was first found in the Baltic Sea in 1992 and now appears in the open Sea in addition to the Gulf of Riga and Neva Estuary. A male is shown in image 9. Females usually have a distinctive 'tip' at the apex of the brood chamber.
Males lack a brood chamber, and, in Lake Ontario, are much smaller than females.
Lake Ontario females are also smaller than those from the Caspian Lake and the Baltic Sea. The picture below includes all three types of animals present in the Lake Ontario population. Body lengths of these individuals are 1.77, 1.48 and 1.12 mm, respectively. Caudal appendage lengths are 8.93, 7.71 and 3.80 mm, respectively. A report on the Cercopagis invasion of Lake Ontario was presented in the January 1999 issue of the Canadian Journal of Fisheries and Aquatic Sciences .