apical ridge
A B C D E F G H I L M N O P R S T U V X Z

A topographic feature of some prorocentroids (desmokonts); it a raised thecal region or thickened margin (an extension of the intercalary band) on the anterior margin of the cell that surrounds or borders the periflagellar area (e.g. P. caribbaeum, P. tropicalis). Oftentimes, this feature can only be viewed via SEM.

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Prorocentrum caribbaeum: thickened apical ridge (arrows) surrounds periflagellar area.

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Prorocentrum tropicalis: thickened apical ridge on left valve borders periflagellar area.