Visual eyes: a quantitative analysis of the photoreceptor layer in deep-sea sharks.

The marine environment presents unique visual challenges for a range of organisms, particularly those dwelling at great depths, where sunlight may either be absent or drop to very low levels. Under these environmental conditions, the visual system must maximise light absorption in order to enhance the detection of prey, predators and potential mates. Using stereological analysis of retinal wholemounts, the distribution and number of photoreceptors (rods) was determined for 5 deep-sea shark species from a range of depths (46-1,500 m).

The retinal topography of three species of coleoid cephalopod: significance for perception of polarized light.

The retinal topography of three species of coleoid cephalopod (one cuttlefish, one squid and one octopus) was investigated to examine and compare the structure, density and organization of the photoreceptors. The aim was to determine if there were areas of increased cell density and/or cell specialization that might be related to lifestyle or phylogeny. The orientation of photoreceptors around the curved surface of the retina was also mapped to reveal how the overall arrangement of cell microvilli might enable the perception of polarized light stimuli.

Visual pigment in the lens eyes of the box jellyfish Chiropsella bronzie.

Box jellyfish (Cubomedusae) possess a unique visual system comprising 24 eyes of four morphological types. Moreover, box jellyfish display several visually guided behaviours, including obstacle avoidance and light-shaft attractance. It is largely unknown what kind of visual information box jellyfish use for carrying out these behaviours.

Spectral sensitivity in a sponge larva.

Cilia at the posterior pole of demosponge larvae are known to cause directional swimming, sometimes in response to light gradients, but so far neither the spectral sensitivity of, nor the molecular basis for, this response has been investigated. We exploited the fact that the larval cilia respond to sudden changes in light intensity, a shadow response, in order to determine the action spectrum of photosensitivity. Our results show that larvae of the haplosclerid sponge Reniera sp.