Chestnut Lamprey

Family: 
Petromyzontidae (lampreys) in the class Agnatha (jawless vertebrates)
Description: 

Chestnut colored eel-like fish that have a cartilaginous, boneless skeleton. Adults have well-developed, rasplike oral disc, seven porelike gill openings, no paired fins and a single nostril. The ammocoetes (the juvenile forms) are eyeless and have a horseshoe-shaped hood as a mouth.

Size: 
Adult length: 10-12 inches; larvae can be 6 inches or more.
Habitat and conservation: 
Large streams and small rivers of the Mississippi River system, and large reservoirs. Ammocoetes (their larvae) are found buried in stable, soft silt and muck of clear flowing streams.
Foods: 
Ammocoetes filter tiny algae and protozoa from the soft sediments and water just above them. Adults attach to sides of a variety of fish including carp, catfishes, sturgeons, paddlefish and sunfishes, where they consume the body fluids of host fish. Several days are required for the lamprey to complete its meal, after which it drops off. The host fish usually does not die as a direct result of the attack but may die of a secondary infection of the wound.
Distribution in Missouri: 
Large streams and small rivers of the Mississippi River system, including the lower Missouri River (below St. Joseph) and the larger streams and reservoirs of the Ozarks.
Status: 
This is the most abundant and widely distributed lamprey in Missouri. Any lamprey found attached to a fish anywhere except the Mississippi River will almost surely be this species.
Life cycle: 
Thought to live for a period of 3 to 6 years in Missouri as ammocoetes (larvae). May live for another 2 years as a mature adult. Adults migrate upstream into small spawning streams. Spawning occurs in shallow pits, which the adults excavate by carrying stones away using their suction-disk mouths. Adults do not feed during or after spawning; once spawning activities are completed, the adults die.
Human connections: 
Lampreys are living remnants of a group of primitive, jawless vertebrates that lived over 350 million years ago. You could argue they are not even really fish: Lampreys are no more closely related to other living fishes than those fishes are to amphibians and other higher vertebrates.
Ecosystem connections: 
Often when we think about "food webs," we picture only those species that completely devour one another. But there is something to be said for parasites, which harm but might not outright kill the organisms that give them sustenance: Their "prey" have a chance to survive after the attack.