Redescription of the Siamese shield leech Placobdelloides siamensis with new host species and geographic range.

The Siamese shield leech Placobdelloides siamensis (Oka, 1917) Sawyer, 1986 (Euhirudinea: Glossiphoniidae) was collected from five new host species, Southeastern Asian Box Turtle (Cuora amboinensis), Yellow-headed Temple Turtle (Heosemys annandalii), Malayan Snail-eating Turtle (Malayemys macrocephala), Mekong Snail-eating Turtle (M. subtrijuga), and Khorat Snail-eating Turtle (M. khoratensis) and was found for the first time in Udon Thani, Thailand. Examination of live leeches provided, for the first time, data on coloration and the combination of parental care behavior, both carrying cocoons and attaching cocoons to the substrate. This species was separated from its congeners based on the following characters: one pair of eyes; spines at proboscis subterminal; mouth terminal on oral sucker; absent plaque in neck region; gonopores located in furrow and separated by two annuli; distinctly triannulated mid-body segments; crop with seven pairs and branched caeca; caudal sucker slightly over half of maximum body width; and strongly dorsal papillae. Phylogenetic relationships based on the COI and ND1 genes were clarified and demonstrated that the species is distinct from others. The original description was amended and the taxonomic history is discussed.