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usp.br Ethanol-preserved specimens represent one of the most common resources for biological research. However, little is known of how ethanol preservation may change tissue morphology and impact the interpretation of trait quantification in structures, such as eyes. While scallop eyes are an interesting system for investigating eye evolution and visual adaptations, cross-species comparisons mainly depend on museum specimens. Therefore, to test whether ethanol-preserved specimens serve as accurate indicators of natural eye morphology, we investigated the effects of preservation on selected traits, such as eye and pupil diameter, in the scallop Argopecten irradians . We also compared ethanol-preserved eyes to paraformaldehyde (PFA)-fixed eyes to investigate possible impacts on retinal morphology. Our results demonstrate that eye size does not change with short-term preservation, whereas pupil size becomes significantly larger, likely due to the contraction of actin fibers during dehydration. When comparing measurements among eyes and treatments, eye size correlates to pupil size, but is not correlated to body size. We found that ethanol-preserved eyes provide close estimates of retinal traits, with similar photoreceptor spacing distance and number of photoreceptor cells, compared to samples fixed in PFA. These findings might also be applicable in the context of other mollusks, especially bivalves and gastropods, with delicate visual systems. Our study provides evidence that ethanol- preserved eyes exhibit tissue-specific differences that should be acknowledged in morphological studies. For example, pupil size should be investigated while accounting for post-preservation effects. Other traits, such as lens shape, are inconsistent and severely impacted by preservation. Finally, eye size and some photoreceptor cell measurements can be helpful to describe natural morphology.