DISTRIBUTION AND INNERVATION OF FACIAL BRISTLES AND HAIRS IN THE FLORIDA MANATEE (TRICHECHUS MANATUS LATIROSTRIS)

Abstract

The distribution and anatomy of sirenian perioral bristles (modified vibrissae) and facial hairs are of interest because of their use during feeding and tactile exploration. In the present study we have identified six fields of perioral bristles on the face of the Florida manatee (T. manatus latirostris), four (U1‐U4) on each side of the upper lips and oral cavity, and two (L1‐L2) on each side of the lower lip pad, inside the oral cavity and rostral to the horny mandibular pad. Each field has a characteristic location, number of bristles, and range of bristle length and diameter. There is a mean of 110 (± 19) bristles per side, with no left‐right differences. Branches of the infraorbital nerve innervate the bases of the largest bristles (U2 group) on the upper bristle pad, and the inferior alveolar nerve supplies the bristles of the lower bristle pad. The dorsal and ventral buccal branches of the facial nerve innervate the superficial facial musculature, which is likely to be involved in bristle eversion and other movements which constitute feeding behavior. Hair is denser in the facial region than on the remainder of the body. Within the face, hair is denser on the oral disk than on the supradisk. The oral disk contains bristle‐like hair, whereas the supradisk region possesses hair that is similar in length and diameter to that on the postcranial body. The mean total of bristles and hairs per face was 1,942. Means for the subregions were 220 (± 39) bristles on the perioral bristle pads, 601 (± 115) bristlelike hairs in the oral disk region, 710 (± 229) typical hairs in the supradisk region, and 411 (± 108) typical hairs on the chin. There were no significant differences between left and right side counts. Facial hair density was inversely correlated with facial area and body size. These data provide new information on the anatomical basis of the exceptional orofacial activities characteristic of manatees during feeding and tactile exploration.

Microstructure and innervation of the mystacial vibrissal follicle‐sinus complex in bearded seals, Erignathus barbatus (Pinnipedia: Phocidae)

“…The total number of bearded seal mystacial F-SCs is similar to the number of perioral bristles in Florida manatees (Reep et al, 1998). However, all hairs on manatees are vibrissal F-SCs and the facial region possesses approximately 2,000 F-SCs (Reep et al, 1998).…”

“…However, all hairs on manatees are vibrissal F-SCs and the facial region possesses approximately 2,000 F-SCs (Reep et al, 1998). In spite of the large number of manatee F-SCs, the mean number of myelinated axons innervating just the mystacial vibrissal array of bearded seals is 2.9 times greater than in the entire facial region of Florida manatees (Reep et al, 2001).…”

Somatosensation, Echolocation, and Underwater Sniffing: Adaptations Allow Mammals Without Traditional Olfactory Capabilities to Forage for Food Underwater

“…As with pinnipeds, sirenians have sensitive vibrissae that help these animals navigate the environment, with the aid of color vision (Griebel and Schmidt, 1996;Newman and Robinson, 2006). The West Indian manatee has over 5300 vibrissae covering its entire body; about 2000 of these vibrissae are located in the facial region (Reep et al, 1998). Manatees use their facial hairs for different functions (Bachteler and Dehnhardt, 1999) and both facial and postfacial vibrissae help the manatee detect hydrodynamic stimuli and navigate its environment (Reep et al, 2011).…”

Tactile Hairs on the Postcranial Body in Florida Manatees: A Mammalian Lateral Line?

“…The facial bristles and hairs are used not only for tactile exploration and discrimination Bachteler and Dehnhardt, 1999] but also for oripulatory grasping of plants during feeding 2000]. Recently, we reported that all the hairs and bristles in the facial region of the Florida manatee are modified vibrissae associated with F-SCs having substantial innervation [Reep et al, 2001]. Dosch [1915] reported that all hairs on the bodies of sirenians were sinus hairs.…”