Morphology of the eyeball from the humpback whale (Megaptera novaeangliae)

Abstract

Aquatic mammals underwent morphological and physiological adaptations due to the transition from terrestrial to aquatic environment. One of the morphological changes regards their vision since cetaceans' eyes are able to withstand mechanical, chemical, osmotic, and optical water conditions. Due to insufficient information about these animals, especially regarding their sense organs, this study aimed to describe the morphology of the Humpback whale (Megaptera novaeangliae) eyeball. Three newborn females, stranded dead on the coast of Sergipe and Bahia, Brazil, were used. Samples were fixed in a 10% formalin solution, dissected, photographed, collected, and evaluated through light and electron microscopy techniques. The Humpback whale sclera was thick and had an irregular surface with mechanoreceptors in its lamina propria. Lens was dense, transparent, and ellipsoidal, consisting of three layers, and the vascularized choroid contains melanocytes, mechanoreceptors, and a fibrous tapetum lucidum. The Humpback whale eyeball is similar to other cetaceans and suggests an adaptation to diving and migration, contributing to the perception of differences in temperature, pressure, and lighting.

Retinal Topography in Two Species of Baleen Whale (Cetacea: Mysticeti)

“…Our description of the eye in the humpback whale is also in accordance with the results of Rodrigues et al [2014] for the same species. Some of the characteristic features of cetacean eyes, especially those of the larger species, are a flattened, thickened cornea, heavily thickened sclera, spherical or near-spherical lens, highly vascularised fibro-adipose bundle surrounding the optic nerve at the back of the eye, and the reflective choroidal tapetum lucidum Supin, 2007, 2009].…”

“…In this study, we found the Bryde's whale and the humpback whale lenses to be non-spherical, with the axial diameter of the lens being approximately 30% shorter than the naso-temporal and dorso-ventral diameters. Similarly, Rodrigues et al [2014] also found that the axial diameter of the lens in the humpback whale was closer to 40% shorter than the naso-temporal and dorso-ventral diameters. Moreover, Zhu et al [2001] and Buono et al [2012] found that the lens axial diameter was substantially shorter than the naso-temporal and dorsoventral diameters in two other mysticete species, the bowhead whale and the southern right whale, respectively.…”

“…Like other mysticetes, Bryde's whales and humpback whales have laterally positioned eyes, located just dorsal to the oral commissure [Zhu et al, 2001;Buono et al, 2012;Rodrigues et al, 2014;Berta et al, 2015]. Of the eyes we examined, the Bryde's whale eye was approximately 1.4 times larger than either of the two humpback whale eyes, with, for example, a naso-caudal transverse diameter of ; c) density are illustrated.…”

Eye, Nose, Hair, and Throat: External Anatomy of the Head of a Neonate Gray Whale (Cetacea, Mysticeti, Eschrichtiidae)

“…For example, the eyeballs of the gray whale are situated lateral and external to the bony orbit, which has been observed in another mysticete ( Eubalaena glacialis (Buono et al, ). However, in a humpback ( Megaptera novaeangliae ) the eyeball is reportedly located within the orbit (Rodrigues et al, ). Compared to a similar sized right whale calf, the gray whale eyeball is nearly twice as long (Table ).…”

“…Similar to studies of the eye morphology of the southern right whale (Buono et al, ). The bowhead (Zhu et al, ) and the humpback (Rodrigues et al, ) and irrespective of ontogenetic age, the gray whale eyeball is shorter mediolaterally (width) than in either dorsoventral (height) or rostro‐caudal (length) directions (Table ). Unfortunately, anatomy of internal ocular structures and histological samples of the retina were unavailable for comparative purposes and determination of visual acuity of Eschrichtius .…”