Comparative anatomy of the ciliary body of the West Indian manatee (<i>Trichechus manatus</i>) and selected species

Natiello, Michelle; Lewis, Patricia; Samuelson, Don

doi:10.1111/j.1463-5224.2005.00408.x

Cited by 6 publications

(8 citation statements)

References 8 publications

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“…Contrary to the majority of mammals that have avascular corneae, blood vessels have been reported throughout the manatee cornea (Harper et al, 2005). Another unusual feature of the manatee's visual system is that the ciliary body contains no muscle fibers (West et al, 1991;Samuelson et al, 1994;Natiello et al, 2005). Further, the angioarchitecture of the ciliary body of the manatee is unique compared to those examined in terrestrial mammals.…”

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confidence: 99%

Ganglion Cell Distribution and Retinal Resolution in the Florida Manatee, Trichechus Manatus Latirostris

Mass

Ketten

Odell

et al. 2011

The Anatomical Record

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The topographic organization of retinal ganglion cells was examined in the Florida manatee (Trichechus manatus latirostris) to assess ganglion cell size and distribution and to estimate retinal resolution. The ganglion cell layer of the manatee's retina was comprised primarily of large neurons with broad intercellular spaces. Cell sizes varied from 10 to 60 lm in diameter (mean 24.3 lm). The retinal wholemounts from adult animals measured 446-501 mm 2 in area with total ganglion cell counts of 62,000-81,800 (mean 70,200). The cell density changed across the retina, with the maximum in the area below the optic disc and decreasing toward the retinal edges and in the immediate vicinity of the optic disc. The maximum cell density ranged from 235 to 337 cells per millimeter square in the adult retinae. Two wholemounts obtained from juvenile animals were 271 and 282 mm 2 in area with total cell numbers of 70,900 and 68,700, respectively (mean 69,800), that is, nearly equivalent to those of adults, but juvenile retinae consequently had maximum cell densities that were higher than those of adults: 478 and 491 cells per millimeter square. Calculations indicate a retinal resolution of $19 0 (1.6 cycles per degree) in both adult and juvenile retinae. Anat Rec, 295:177-186, 2012. V V C 2011 Wiley Periodicals, Inc.Key words: manatee; Trichechus manatus; eye; retina; ganglion cells; cell topography; cell size; retinal resolution; visual acuityThe Sirenia order includes the manatee, dugong, and the extinct Steller cow. Sirenians are adapted to salt and fresh water habitats and, unlike other marine mammals, are exclusively herbivorous. Consequently, they have a range of unique anatomical, physiological, and behavioral adaptations. Further, all species of the order are endangered. The West Indian manatee is a slow grazer that inhabits the coastal areas and rivers of the Caribbean basin (Bertram and Bertram, 1962;Hartman, 1979; Nowak, 1991). The Florida manatee, Trichechus manatus latirostris, is a subspecies of the West Indian manatee, T. manatus. Knowing more about their sensory abilities, including their visual abilities, is of interest not only for basic evolutionary research but also for planning strategies for conserving this highly endangered species.

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confidence: 99%

Ganglion Cell Distribution and Retinal Resolution in the Florida Manatee, Trichechus Manatus Latirostris

Mass

Ketten

Odell

et al. 2011

The Anatomical Record

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“…As noted previously, the aquatic pilot whale, like the manatee, also has a great deal of vasculature in its ciliary processes 5 . However, some variations from the manatee exist.…”

Section: Discussionmentioning

confidence: 83%

“…It has been thought that the encapsulated corpuscles are a type of mechanoreceptor. Because of the lack of ciliary muscle in the dolphins and whales it has been thought that these structures function in place of the muscle to regulate aqueous outflow 5,24 . These encapsulated corpuscles have been observed to lie near large vessels, particularly those involved in posterior collateralization 5 .…”

Section: Discussionmentioning

confidence: 99%

“…Because of the lack of ciliary muscle in the dolphins and whales it has been thought that these structures function in place of the muscle to regulate aqueous outflow 5,24 . These encapsulated corpuscles have been observed to lie near large vessels, particularly those involved in posterior collateralization 5 . Perhaps these structures further allow for varying levels of accommodation by controlling the pressure exerted on the vessels involved in aqueous humor dynamics.…”

Section: Discussionmentioning

confidence: 99%

“…The present study examines the angioarchitecture of the ciliary body of the West Indian manatee by three‐dimensional reconstruction. This study compares this angioarchitecture to that of the ciliary bodies previously described in mammals, being mostly terrestrial, but including our recent descriptions of the amphibious hippopotamus, and aquatic bottle‐nosed dolphin 3–5 . Through this further exploration of the eye, trends that may exist due to evolutionary factors can be examined.…”

Section: Introductionmentioning

confidence: 98%

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Three‐dimensional reconstruction of the angioarchitecture of the ciliary body of the West Indian manatee (Trichechus manatus)

Natiello

Samuelson

2005

Veterinary Ophthalmology

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Review of sensory modalities of sirenians and the other extant Paenungulata clade

Moore

Hartstone‐Rose

Gonzalez‐Socoloske

2021

The Anatomical Record

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Extant members of Paenungulata (sirenians, proboscideans, and hyracoideans) form a monophyletic clade which originated in Africa. While paenungulates are all herbivorous, they differ greatly in size, life history, and habitat. Therefore, we would expect both phylogenetically related similarities and ecologically driven differences in their use and specializations of sensory systems, especially in adaptations in sirenians related to their fully aquatic habitat. Here we review what is known about the sensory modalities of this clade in an attempt to better elucidate their sensory adaptations. Manatees have a higher frequency range for hearing than elephants, who have the best low‐frequency hearing range known to mammals, while the hearing range of hyraxes is unknown. All paenungulates have vibrissae assisting in tactile abilities such as feeding and navigating the environment and share relatively small eyes and dichromatic vision. Taste buds are present in varying quantities in all three orders. While the olfactory abilities of manatees and hyraxes are unknown, elephants have an excellent sense of smell which is reflected by having the relatively largest cranial nerve related to olfaction among the three lineages. Manatees have the relatively largest trigeminal nerve—the nerve responsible for, among other things, mystacial vibrissae—while hyraxes have the relatively largest optic nerve (and therefore, presumably, the best vision) among the Paenungulata. All three orders have diverged significantly; however, they still retain some anatomical and physiological adaptations in common with regard to sensory abilities.

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Comparative anatomy of the ciliary body of the West Indian manatee (Trichechus manatus) and selected species

Cited by 6 publications

References 8 publications

Ganglion Cell Distribution and Retinal Resolution in the Florida Manatee, Trichechus Manatus Latirostris

Ganglion Cell Distribution and Retinal Resolution in the Florida Manatee, Trichechus Manatus Latirostris

Three‐dimensional reconstruction of the angioarchitecture of the ciliary body of the West Indian manatee (Trichechus manatus)

Review of sensory modalities of sirenians and the other extant Paenungulata clade

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