Title: A Comparative Study of the Tracheal Michroanatomy in Harbor Seals (Phocavitulina), COmmon Dolphin (Delphis delphis), and Florida Manatee (trichechus manatus latirostris)

Abstract: The trachea plays an important role in the transportation of gases in and out of the lungs as well as preventing foregoing objects from entering the lungs. Marine mammals have a specialized respiratory system adapted for life in aquatic environments. Previous studies have examined the gross anatomical structure of different marine mammal species and the microanatomy of the harbor seal alone. In this study we describe and compare the tracheal microanatomy for the harbror seal (Phoca vitulina), common dolphin (Delphinus delphis), and Florida manatee (Trichechus manatus latirostris). A gross examination was carried out to measure the thickness of the cartilage rings and the condition of the epithelium. Frozen tissue samples were sectioned using a cryostat and the tissue was stained with H&E, Gomori’s trichrome, and toludine blue. Among the three species, the Florida manatee was found to the thickest cartilage rings, ranging between 8.0-9.0mm while the harbor seal and common dolphin ranged between 0.94 mm and 1.35 mm. Additionally, vasculature was identified within the cartilage rings of the Florida manatee which is unusual for mammals as cartilage is typically avascular. Crypts were identified within the Florida manatee that appear to have similar morphology to crypts found in the intestines. Crypts or undulations in the epithelium were identified within the common dolphin as well. Furthermore, there was abundant vasculature in all species examined with the Florida manatee and common dolphin both having long veins and the Florida manatee having the largest arteries. In recent years, respiratory illnesses in marine mammals have been on the rise across the globe. With this rise, it is important to understand the normal microanatomy for marine mammals before the abnormal in the case of respiratory illness can be identified.