Date of Award

Spring 2022

Document Type

Open Access Dissertation


Biological Sciences

First Advisor

Daniel I. Speiser


Vision is usually thought to be inextricably linked to cephalization; however, certain species of invertebrates deviate from this canonical association by having noncephalized visual systems that are composed of numerous photoreceptive organs distributed across their body paired with centralized, decentralized, or distributed neural architectures. In contrast to cephalized visual systems, we know comparatively little about the visual processing and visually-mediated behaviors of animals with distributed visual systems which are crucial towards understanding how and why these animals see with so many eyes. In this dissertation, we investigate the visual neuroanatomy and visually-mediated behaviors of two different marine molluscs with distributed visual systems - the West Indian fuzzy chiton Acanthopleura granulata and the Atlantic bay scallop Argopecten irradians.

The chiton A. granulata has a distributed visual system composed of hundreds of small imaging forming eyes embedded within their eight dorsal shell-plates. Using behavioral trials, we found that A. granulata demonstrates a visual acuity of 6° and responds to looming stimuli which are defined by contrasting angles of polarization. Using neural tracing and immunohistochemistry, we found that the optic nerves form a distributed visuotopic map along the lateral neuropil, which is a tissue layer which circumnavigates the body, and that this structure has an additional tissue layer that is absent in other species of chiton.

The bay scallop A. irradians has a distributed visual system composed of dozens of complex, reflecting camera-type eyes arrayed along its mantle tissues. Using neural tracing techniques, we found that the optic nerves innervate the cortical surface of the lateral lobes of the visceral ganglion to form a discrete somatotopic map. By using behavioral trials, we found that A. irradians demonstrate spatial vision (i.e. the ability to locate visual cues) by extending their sensory tentacles towards and tracking visual stimuli as small as 5°.

These two animals with different types of distributed visual systems present two novel approaches towards visual integration and processing. A. granulata appears to construct a decentralized visuotopic map to support decentralized visual-motor circuits, whereas A. irradians appears to construct a centralized spatiotopic map which it uses to guide complex decentralized visually-mediated behaviors.

Available for download on Friday, May 31, 2024

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