Spirhapalum siamensis n. sp. obtained from the heart of the Malayan box turtle, Cuora amboinensis, from western Thailand is described. This blood fluke differs from the 2 previously known species of Spirhapalum in its larger overall body size, constricted mid-body, greater number of pre-ovarian testes, ceca that loop anteriorly from the cecal bifurcation before turning to the posterior, and the relatively smaller size of its ventral sucker. A phylogenetic analysis using molecular characters places the new species in the basal clade of tetrapod blood flukes, more derived than Spirhapalum polesianum, but less derived than Spirorchis spp.