Figure 1. A cyprid of Semibalanus balanoides.

A) A low power light micrograph of a cyprid with frontal antennules and thoracic swimming appendages visible; arrows point to the third segments bearing the antennular discs. B) Detail of antennular discs used for adhesion. C) SEM; near medial view of the third antennular segment; narrow velar flaps encircle the third segment reaching to the periphery of the antennular disc. D) Face-on-view of the villus-covered antennular disc. E) Detail from the rim of the attachment disc where velar flaps were missing, allowing estimation of length of the villi.