<b>Comparative Genomics Unveils Unique Antithrombotic Gene Expansion in </b><b><i>Haemadipsa yanyuanensis</i></b>

Terrestrial leeches of the family Haemadipsidae are obligate blood-feeding annelids that primarily parasitize vertebrates, including mammals, in tropical and subtropical forests. Although they hold ecological significance and potential biomedical value, the molecular mechanisms underlying their blood-feeding adaptations, especially their anticoagulant and thrombolytic systems, remain poorly characterized. In this study, we present the first chromosome-level genome assembly of the terrestrial leech <i>Haemadipsa yanyuanensis</i>, generated using Nanopore sequencing, Illumina Hi-C, and transcriptomic data. The <i>H. yanyuanensis</i> genome assembly (165.32 Mb, 9 chromosomes) exhibits high completeness (BUSCO score: 97.6%) and encodes 193 antithrombotic genes spanning 15 families. Compared to medicinal leeches, this represents a 2.2- to 2.7-fold increase in gene count but a reduction in family diversity. Notably, H. yanyuanensis displays at least 8-fold expansions in key anticoagulant families (bdellin, LDTI, and LCI) and harbors lineage-specific innovations, including a progranulin gene containing 122 cysteine residues and extended tandem repeats. Our study provides the first genomic blueprint of a terrestrial leech and the most comprehensive catalog of Haemadipsa-derived antithrombotic molecules to date. The identified genes, particularly those with exceptional copy numbers and novel domains, offer valuable templates for developing next-generation anticoagulant and thrombolytic drugs, addressing unmet needs in cardiovascular therapy.