Functional differences between the extraordinary eyes of deep-sea hyperiid amphipods

The ocean’s midwater is a uniquely challenging yet predictable and simple visual environment. The need to see without being seen in this dim, open habitat, has led to extraordinary visual adaptations. To understand these adaptations, we compared the morphological and functional differences between the eyes of three hyperiid amphipods – Hyperia galba, Streetsia challengeri, and Phronima sedentaria. Combining micro-CT data with computational modelling, we mapped visual field topography and predicted detection distances for visual targets viewed in different directions across mesopelagic depths. Hyperia’s eyes provide a wide visual field optimized for spatial vision over short distances, while Phronima and Streetsia’s eyes have the potential to achieve greater sensitivity and longer detection distances using spatial summation. These improvements come at the cost of smaller visual fields, but this loss is compensated for by a second pair of eyes in Phronima and with behaviour in Streetsia. ..., Specimens were euthanized by being immersed in iced seawater or the addition of a few drops of 95% ethanol to their holding tank. The heads and anterior-most segments of Hyperia and Phronima were dissected from the body, then fixed in 4% seawater buffered formalin (Hyperia) or 2% cacodylate buffered glutaraldehyde (Phronima). Hyperia and Phronima specimens were run through a dehydration series then stained with a 0.5% phosphotungstic acid (PTA) solution in 70% ethanol for 30 days before scanning. Streetsia specimens were fixed in 4% phosphate buffered paraformaldehyde and stained with an aqueous 1% w/v iodine and 2% w/v potassium iodide solution for seven days. Specimens were mounted in 500 µl sealed Eppendorf tubes stabilized with either minute blocks of foam or 1% low temperature gelling agarose. Hyperia and Phronima specimens were scanned using a GE Phoenix v|tome|x M 240/180 kV Dual Tube micro-CT at the Smithsonian National Museum of Natural History at 80 – 90 kV and 2.65 – 4.26 W, ..., , # Functional differences between the extraordinary eyes of deep-sea hyperiid amphipods

[https://doi.org/10.5061/dryad.prr4xgxtd](https://doi.org/10.5061/dryad.prr4xgxtd)

* The .nii files included in this data set were acquired using X-ray tomography. Each file contains a stack of greyscale images that can be imported into 3D image visualization software. X-ray tomography was conducted on two specimens of three iodine-stained hyperiid amphipods.
* The MATLAB files included in this dataset contain the data extracted from the .nii files using our custom-made MATLAB software which has also been uploaded here. These data were also used in our optical models conducted using MATLAB scripts that have also been uploaded here.