Colony Growth Pattern in Electra pilosa (Linnaeus) and Comparable Encrusting Cheilostome Bryozoans

Colony growth pattern is described in E. pilosa , an abundant cheilostome bryozoan commonly found as an epiphyte of Laminaria. Each zooid has 4 potential budding loci—one distal, two lateral and one proximal. The ancestrula buds daughter zooids from all of these loci; the two lateral buds appear first, followed by the distal bud and, after a long delay, the proximal bud. The laterally budded zooids curve inwards as they grow to form a triad with their distally budded sibling zooid. ‘Mature’ multiserial colonies growing on flat substrata consist of a series of radially diverging sectors. Each sector has an axis, generally of 3 parallel rows of zooids, flanked by wings consisting of rows of zooids originating as lateral buds from the section axis which infills the area between the axes. Occasional colonies occur with uniserial or semiuniserial growth patterns. These resemble colonies of the obligatory uniserial species Pyripora catenularia and poorly fed colonies of the related Conopeum tenuissimum , which is normally multiserial like E. pilosa. The ‘composite multiserial’ colonies of E. pilosa differ in several respects from ‘unitary multiserial’ colonies characteristic of most sheet‐like cheilostomes, including the well‐known Membranipora membranacea. Composite and unitary multiserial growth patterns may have evolved independently from uniserial ancestors.