Table 1.

Variations in the trophoblast comprising the interhemal area of the chorioallantoic placenta.

Placental Type	Trophoblast Component	Examples
Hemomonochorial	Syncytial trophoblast, villous	Armadillo; higher primates
	Syncytial trophoblast, labyrinthine	Most hystricomorph rodents (e.g. guinea pig, capybara); sciuromorph rodents (squirrels)
	Cellular trophoblast	Hyraxes; spiny tenrecs (e.g Echinops); mollosid bats (late gestation); some myomorph rodents (Zapus, Jaculus)
Hemodichorial	Syncytial (maternal facing) and cellular trophoblast	Lagomorphs; vespertilionid bats
Hemotrichorial	Cellular trophoblast (maternal facing) and two layers of syncytial trophoblast	Most myomorph rodents (e.g. rat, mouse)
Endotheliochorial	Syncytial trophoblast (fenestrated)	Sloths; shrews (insectivores)
	Syncytial trophoblast (nonfenestrated)	Carnivores and pinnipeds
	Cellular trophoblast	Elephants; some sciuromorph rodents (Dipodomys, Microdipodops); some bats (Natalus, Saccopteryx)
Epitheliochorial	Cellular trophoblast only	Lower primates; pangolin; some artiodactyls (e.g. pig)
	Cellular trophoblast with trophoblastic girdle cells	Equids (perissodactyls, e.g. horse)
Synepitheliochorial	Cellular trophoblast; fusion of binucleate trophoblastic cells with uterine epithelium	Ruminants (artiodactyls, e.g. sheep, cow)