Abnormalities in the development of monograptid colonies

Abstract

Examples of abnormalities and regeneration in Wenlock Monograptidae are described and illustrated. The sicula displays deformations of the dorsal processes, swellings of virgula or extremely numerous internal rings. Some thecae reveal deformed apertures various excrescences and shortenings. Excessive growth and reduction of lateral apertures are very common. Specimens with split of virgulae have also been found. These phenomena seem to be common among graptolites but their origin is not very clear, each case requiring a separate interpretation. The only exception is regeneration whose mechanism is the best studied so far.