Ocelloid

An ocelloid is a subcellular structure found in the family Warnowiaceae (warnowiids), which are members of a group of unicellular organisms known as dinoflagellates.

The ocelloid is analogous in structure and function to the eyes of multicellular organisms, which focus, process and detect light.

[5] Ocelloids contain subcomponents analogous to eye structures including the lens, cornea, iris, and retina.

[6][7][8] Due to the strong structural resemblance between the ocelloid and metazoan eyes, it has long been speculated that the ocelloid functions as a photoreceptor; however, this is difficult to determine experimentally because warnowiids cannot be cultured in the laboratory, and isolates from natural habitats degrade quickly.

[1][4] The molecular evidence is compelling that ocelloids are composed of multiple endosymbionts: mitochondria and at least one type of plastid.

An image of a single cell featuring a large nucleus and an ocelloid, which is composed of a roundish "lens" and a darkly pigmented disc-shaped retinal body.
A light micrograph of an ocelloid-containing dinoflagellate. The nucleus is marked n , the ocelloid is indicated with a double arrowhead, and a posterior cell extension is indicated with an arrow; scale bar = 10 μm. [ 1 ]
A close-up image of an ocelloid.
A micrograph of a single ocelloid; scale bar = 5 μm. [ 1 ]
Grayscale electron micrograph of an ocelloid in its cellular context. Due to the microscopy technique used, the normally translucent hyalosome appears almost as darkly stained as the retinal body.
A negative staining transmission electron micrograph of an ocelloid (white box), indicating the hyalosome (H) and retinal body (R), as well as a portion of the piston (Ps). Scale bar = 10 μm. [ 5 ]
Grayscale diagrams of the structures of the ocelloid and vertebrate eye, showing analogous positional relationships between the hyalosome/lens and retinal body/retina.
Comparison between the structures of the ocelloid (1) and the vertebrate eye (2). Components are indicated as the hyalosome (H), retinal body/retina (R), and crystallin lens (C). [ 5 ]