Marine Animal Encyclopedia
Forming single filaments or small bundles, bacteria of the genus Calothrix are widespread in oceans everywhere. Unlike those of Oscillatoria and Trichodesmium, the filaments of Calothrix crustacea have a broad base and a pointed tip that ends in a transparent hair. The filament has a firm or jellylike coating, which is often made up of concentric layers that may be colorless or yellow-brown. Unusually, the filament grows in much the same way as a plant root, its growth being confined to a special region just behind the tip, called a meristem. Sometimes, the filament sheds the tapering tip above the growth region, enabling Calothrix crustacea to reproduce asexually by casting off fragments called hormogonia from the meristem. These fragments are able to form new filaments far away from the parent. These kinds of cyanobacteria often form slimy coatings on coastal rocks and seaweeds. At least one species of Calothrix is known to make up the photosynthetic part of some rocky shore lichens, such as Lichina pygmaea (see Black Tufted Lichen).