Erythropoiesis and granulopoiesis in the West Indian manatee, Trichechus manatus (Mammalia: Sirenia).
The West Indian manatee, Trichechus manatus, has amedullary, pachyostotic long bones. Since marrow cavities of the long bones typically are the locations of hemopoiesis in adult mammals, the manatee has evolved an alternative primary site of hemopoiesis. Histological examinations of spleens, livers, kidneys, and vertebral bodies indicate that the last-named location is the main site of erythropoiesis and granulopoiesis in T. manatus. This conclusion is based on the presence in the vertebrae of bone-marrow-containing diagnostic cell types including erythroblasts, megakaryocytes, and myelocytes, which are the precursor cells of erythrocytes, platelets, and granular leukocytes, respectively. No developing lymphocytes were found, so that the location of lymphopoiesis remains unknown.
D000818:Animals; D004900:Erythroblasts / Q000648:ultrastructure; D004920:Erythropoiesis; D006098:Granulocytes / Q000502:physiology*; D008322:Mammals / Q000502:physiology*; D008533:Megakaryocytes / Q000648:ultrastructure; D013131:Spine / Q000166:cytology / Q000502:physiology