Eye morphology and optics of the double‐eyed mysid Euchaetomera typica

Abstract

 AbstractGaten, E., Herring, P. J. and Shelton, P. M. J. 2002. Eye morphology and optics of the double-eyed mysid Euchaetomera typica . -Acta Zoologica (Stockholm) 83 : 221-230The structure and optics of the mesopelagic double-eyed mysid crustacean Euchaetomera typica Sars, 1884 are described for the first time. The lateral eye is a typical refracting superposition eye with a wide field of view (172 ° ) and low resolution (interommatidial angle of 7.3 ° ). The antero-dorsal part of the eye is elongated due to the extension of the clear zone. This dorsal eye has a restricted field of view (33 ° ) but much higher resolution (1.5 ° ). The dorsal eye also uses refracting superposition optics, although the optical array is unusual as many of the peripheral ommatidia lack crystalline cones. The centre of curvature of the cornea is in front of the flattened rhabdom layer whereas the axes of the crystalline cones are centred on a point about twice as deep as the rhabdom layer. This results in a well-focused eye, free of spherical aberration. There is a remarkable similarity in eye structure between this species and some mesopelagic double-eyed euphausiid crustaceans.

Contrast enhancement through structural variations in the rhabdoms of oplophorid shrimps

“…The attenuation of light with depth, resulting in the absence of usable daylight below 1000 m, means that sensitivity must be maximized. The asymmetrical distribution of light in the deep seas, with the downwelling irradiance up to 1000 times brighter than the upwelling irradiance, is often correlated with structural modifications along the dorso-ventral plane of the eye (Lythgoe, 1979;Land et al, 1979;Land, 1989;Gaten et al, 2002). In addition, scattering of light results in a low contrast visual scene in which any target is obscured by veiling light.…”

Exceptional Variation on a Common Theme: The Evolution of Crustacean Compound Eyes

“…4c) and the double-eyed euphausiids (Fig. 6) and mysids (Gaten et al 2002)-which occupy similar ecological environments in the deep sea-illustrate a functional convergence imposed by similar evolutionary pressures on the visual system to sample in different directions in space for different purposes.…”

Laboratory-Based Observations of Behaviour in Northern Krill (Meganyctiphanes norvegica Sars)

“…This gives a value of around 2.9° which is much lower than is usually found in the upper eyes of euphausiids (1. 2° -Land et al, 1979) or mysids (1.5° - Gaten et al, 2002) from deeper water. This is assuming ideal optics and adequate lighting -in reality the resolution would be much poorer due to imperfections in the optics.…”