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Cephalopod NeurobiologyNeuroscience Studies in Squid, Octopus and Cuttlefish$
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N. Joan Abbott, Roddy Williamson, and Linda Maddock

Print publication date: 1995

Print ISBN-13: 9780198547907

Published to Oxford Scholarship Online: March 2012

DOI: 10.1093/acprof:oso/9780198547907.001.0001

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The firefly squid, Watasenia scintillans, has three visual pigments

The firefly squid, Watasenia scintillans, has three visual pigments

Chapter:
(p.491) 30 The firefly squid, Watasenia scintillans, has three visual pigments
Source:
Cephalopod Neurobiology
Author(s):

Masatsugu Seidou

Kinya Narita

Masanao Michinomae

Yuji Kito

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780198547907.003.0336

This chapter describes the three visual pigments and their distribution in the retina of Watasenia scintillans. These have absorbance maxima at 471 nm, 484 nm, and 501 nm. The 484 nm pigment is based on retinal, the 501 nm pigment on 3-dehydroretinal, and the 471 nm pigment on the novel chromophore 4-hydroxyretinal. In the dorsal retina, the rhabdomes are 200 μm thick and consist of photoreceptor outer segments containing the visual pigment with retinal (A1 pigment). In the specific region of the ventral retina receiving downwelling light, the rhabdomes, the photoreceptor outer segments are 600 μm thick. The distal outer segment layer, 400 μm thick from the retinal surface, contains the yellowish visual pigment based on 4-hydroxyretinal (A4 pigment) and the proximal outer segment layer contains the pinkish visual pigment based on 3-dehydroretinal (A2 pigment). It was observed that while one type of photoreceptor had rhabdomes only in the proximal outer segment layer, the other types had rhabdomes only in the distal outer segment layer. From these results, it was concluded that these visual pigments seem to be contained in separate photoreceptor cells. Due to the structure of the stratified outer segment layer, the A4 pigment layer acts as a yellowish filter on the photoreceptor cells containing A2 pigment, and this filtering effect shifts the wavelength of maximal photosensitivity of the photoreceptors to 550 nm. The A2 pigment photoreceptor cell with photosensitivity shifts towards longer wavelength, and is useful for detecting this green light. The existence of the three visual pigments suggests that the squid may have the ability of colour discrimination.

Keywords:   Watasenia scintillans, Colour wavelength, photoreceptor cell, photosensitivity, rhabdomes, chromophore

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