The markopolio split from its ancestor, the blue buckler. It has developed into a fatal disease among "roaches". While it can infect gilltails and gillfins it mainly infects "roaches". It is spread via feces and is consumed orally in the water. Once inside it infects motor neurons which in "roaches" means that their legs become paralyzed and thus cannot walk anymore. Over time the populations of roaches were infected not only by their own kind but their "beakworm" relatives. Over and over the disease wiped out a little more and a little more until the roach population could no longer compete with other creatures. The species that become extinct are; the east mekoroach, mekoroach, tikoroach, gilllegs, jawbreaker roach, dredger.
Note that the jawbreaker roach got infected when the beach population entered the waters of Huggs Coast at Vivus Island Beach. It quickly spread within the small island population causing all of them to die a horrible death paralyzed on the ground. The gilltails and gillfins that get infected gain semi-paralysis but since their motor neurons are different than the "roaches" they can recover quickly. All other species are unaffected by this.