ERGA-BGE reference genome of Placobdella costata: an ectoparasitic glossiphoniid leech of freshwater turtles with a Palearctic distribution

Placobdella costata , commonly known as the European pond turtle leech, is one of two Palearctic representatives of its genus, with most recognised diversity being North American. Current molecular evidence supports the hypothesis of a single dispersal event from North America to Europe. Placobdella costata is primarily a blood-feeding ectoparasite of freshwater turtles and has been identified as a vector of the apicomplexan Haemogregarina stepanowi. Like other blood-feeding glossiphoniids, it hosts a nutritional symbiont in specialised organs called bacteriomes. We expect the genome of P. costata to not only contribute to the hitherto poor genomic resources available for this leech family, but to also serve as a starting point to explore the evolution of new organs (such as the bacteriome), body parts (such as a proboscis), and biological traits (such as parental care), as well as to disentangle the host-microbe interactions between this leech and its nutritional symbiont. The genome of P. costata was assembled into two haplotypes. Results are reported for the primary haplotype, here used as reference. A total of 18 contiguous chromosomal pseudomolecules were assembled from the genome sequence along with the mitochondrial genome. This chromosome-level assembly encompasses 0.48 Gb, composed of 688 contigs and 29 scaffolds, with contig and scaffold N50 values of 1.76 Mb and 31.5 Mb, respectively.