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Vertebrate reproductive science and technology

Placentation in the Amazonian manatee (Trichechus inunguis)

A. M. Carter A , M. A. Miglino B F , C. E. Ambrosio B , T. C. Santos B , F. C. W. Rosas C , J. A. d’Affonseca Neto C , S. M. Lazzarini D , A. F. Carvalho E and V. M. F. da Silva C
+ Author Affiliations
- Author Affiliations

A University of Southern Denmark, J. B. Winsloewsvej 21, DK 5000 Odense, Denmark.

B University of Sao Paulo, Faculty of Veterinary Medicine and Animal Science, Av. Prof. Dr. Orlando Marques de Paiva 87, Cidade Universitária, 05580-270 Sao Paulo, SP, Brazil.

C National Institute of Amazonian Research, Av. André Araújo, 2936, 69083-000 Manaus, AM, Brazil.

D Centre of Protection and Research of Aquatic Mammals, Rodovia Manaus-Caracarai Km 122, Balbina, 69736-000 Presindente Figueiredo, AM, Brazil.

E School of Veterinary Medicine, Av. Octávio Bastos, Nova São João, 13870-040 Sao João da Boa Vista, SP, Brazil.

F Corresponding author. Email:

Reproduction, Fertility and Development 20(4) 537-545
Submitted: 18 January 2008  Accepted: 4 March 2008   Published: 11 April 2008


Evidence from several sources supports a close phylogenetic relationship between elephants and sirenians. To explore whether this was reflected in similar placentation, we examined eight delivered placentae from the Amazonian manatee using light microscopy and immunohistochemistry. In addition, the fetal placental circulation was described by scanning electron microscopy of vessel casts. The manatee placenta was zonary and endotheliochorial, like that of the elephant. The interhaemal barrier comprised maternal endothelium, cytotrophoblasts and fetal endothelium. We found columnar trophoblast beneath the chorionic plate and lining lacunae in this region, but there was no trace in the term placenta of haemophagous activity. The gross anatomy of the cord and fetal membranes was consistent with previous descriptions and included a four-chambered allantoic sac, as also found in the elephant and other afrotherians. Connective tissue septae descended from the chorionic plate and carried blood vessels to the labyrinth, where they gave rise to a dense capillary network. This appeared to drain into shorter vessels near the chorionic plate. The maternal vasculature could not be examined in the same detail, but maternal capillaries ran rather straight and roughly parallel to the fetal ones. Overall, there is a close resemblance in placentation between the manatee and the elephant.

Additional keywords: Afrotheria, haemophagous organ, phylogeny, Sirenia.


These studies were supported by The Carlsberg Foundation, Denmark (A.M.C.), Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP; M.A.M.) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq; M.A.M. and V.M.F.S.). The authors are very grateful to Dr Allen C. Enders for his valuable input on the interpretation of the fine structure of the placenta. The authors thank the team of INPA and CPPMA for their dedicated work with the captive manatees.


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