Ocellulimbus

An ocellulimbus is a type of porefield found on a valve apex. Externally, the ocellulimbus appears to be set into the apex of the valve. Like other porefields, the ocellulimbus likely secretes mucopolysaccharides which are used to attach the diatom to a substrate or to sibling cells. From Latin for little eye (ocellus) and border (limbus). The plural is ocellulimbi.

Ocellulimbi are found in several araphid genera such as Catabombas, Ctenophora, Pseudostaurosira, Synedra, and Tabularia.

Williams (1986) defined ocellulimbus as a "plate set into the polar valve mantle".

Porefield Types

apical porefield - separated from valve striae by a narrow hyaline area; occurs at valve apex of some araphid (e.g. Diatoma) and some raphid genera (e.g. Cymbella)

ocellulimbus - porefield set into the apex of a valve (e.g. Pseudostaurosira)

ocellus - porefield with a distinct hyaline rim (e.g. Pleurosira)

pseudocellus - porefield lacking demarcation and with pores decreasing in size (e.g. Terpsinoë)

See ocellus, porefield, and pseudocellus for more detail.

Citations

Ocellulimbus — Scanning electron micrographs of two valves of *Pseudostaurosira parasitica*. An ocellulimbus is present at each pole.

Ocellulimbus External — External view of the ocellulimbus of *Stauroforma inermis*. Material from the Thames River estuary, Connecticut.

Ocellulimbus Internal — Internal view of the ocellulimbus of *Pseudostaurosira parasitica*.