Retinal development and ommin pigment in the cranchiid squid Teuthowenia pellucida (Cephalopoda: Oegopsida)
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Evans, AB
Acosta, ML
Bolstad, K
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PLOS One
Abstract
The cranchiid Teuthowenia pellucida, like many deep-sea squid species, possesses large
eyes that maximise light sensitivity in a nearly aphotic environment. To assess ontogenetic
changes in the visual system, we conducted morphometric and histological analyses of the
eyes using specimens from New Zealand collections. While the ratio between eye diameter
and mantle length maintained a linear relationship throughout development, histological sections
of the retina revealed that the outer photoreceptor layer became proportionally longer
as the animal aged, coincident with a habitat shift into deeper, darker ocean strata. Other retinal
layers maintained the same absolute thickness as was observed in paralarvae. Granules
of the pigment ommin, normally located in the screening layer positioned at the base of
the photoreceptors, were also observed at the outer end of the photoreceptor segments
throughout the retina in young and mid-sized specimens. Early developmental stages of this
species, dwelling in shallow waters, may therefore rely on migratory ommin to help shield
photoreceptors from excess light and prevent over-stimulation. The oldest, deeper-dwelling
specimens of T. pellucida examined had longer photoreceptors, and little or no migrated
ommin was observed; we suggest therefore that short-term adaptive mechanisms for bright
light conditions may be used primarily during epipelagic, early life stages in this species.
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PLoS ONE 10(5): e0123453. doi:10.1371/journal.pone.0123453
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© 2015 Evans et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.