Scientists find seven new leech species that live inside freshwater mussels

Nov. 11 (UPI) -- If you eat freshwater mussels, you might open a shell to find one of seven newly named leech species. Yummy.

Between 2002 and 2018, Arthur Bogan, research curator of mollusks at the North Carolina Museum of Natural Sciences, recruited collaborators from all over the globe to collect freshwater mussels, sample DNA and document what they found inside.

The project revealed seven new species of leeches. According to Ivan N. Bolotov, scientist of the Federal Center for Integrated Arctic Research of the Russian Academy of Sciences and one of Bogan's collaborators, at least two of the species should be classified as obligate inhabitants of the freshwater mussel's mantle cavity. These species cannot complete their life cycle without their bivalve host.

"It has been suggested that the primary selective pressure driving the evolution of parental care in leeches may have been predation on leech eggs and juvenile stages," Bolotov said in a news release. "From this point of view, [this lifestyle] could be considered a progressive evolutionary trait in brooding behavior helping to protect juvenile stages from predators."

Scientists compared the modern leech species to a leech fossil from the mid-Triassic to better understand how the animal has evolved. Their analysis, detailed Monday in the journal Scientific Reports, suggests leeches are slow-evolving creatures.

"The reliable mutation rates obtained by us are of great importance to future evolutionary studies of these worms," Bolotov said.

Though all of the species were found inside freshwater mussels, analysis of the stomach contents of each leech suggests the worms periodically leave their hosts to collect the blood of freshwater fish species.

Along with amphibians, like newts and salamanders, mussels are one of the most imperiled groups of freshwater animals. The latest findings suggest their decline could have greater ecological implications than previously realized.