Adaptations in the Structure and Innervation of Follicle-Sinus Complexes to an Aquatic Environment as Seen in the Florida Manatee (Trichechus Manatus Latirostris)

The study examined the structure and innervation of follicle-sinus complexes (FSCs) in the Florida manatee, revealing adaptations for their aquatic environment. Manatee FSCs, which are larger in proportion to their vibrissae, have a variety of innervation types, including C, Adelta, and Abeta fibers with Merkel, club, and longitudinal lanceolate endings, but lack reticular and spiny endings. Unique to manatees are two types of Abeta-fiber endings: large-caliber axons with spindle-like endings and smaller caliber fibers resembling Golgi tendon organs. The largest perioral vibrissae, used for grasping, have a well-developed medullary core with dense small-fiber innervation similar to tooth pulp. These findings suggest that manatee vibrissae are highly specialized for tactile sensation in an aquatic environment.