Chitinozoans are bottle-shaped marine microfossils which thrived during the Ordovician, Silurian, and Devonian periods. They often have root-like structures at the base of the 'flask'. They were first described in 1931 by the German micropaleontologist Alfred Eisenack. Their fossils are found in large numbers (up to 140 per gram of rock) in sedimentary rocks across the globe. They have not yet been scientifically classified, and there still isn't any general agreement about what kind of lifeforms they were, or even if they were a distinct species (as opposed to (e.g.) 'egg sacs' of some other creature.)
Chitinozoa (singular: chitinozoan, plural: chitinozoans) are a taxon of flask-shaped, organic walled marine microfossils produced by an as yet unknown animal. Common from the Ordovician to Devonian periods (i.e. the mid-Paleozoic), the millimetre-scale organisms are abundant in almost all types of marine sediment across the globe. This wide distribution, and their rapid pace of evolution, makes them valuable biostratigraphic markers.
Their bizarre form has made classification and ecological reconstruction difficult. Since their discovery in 1931, suggestions of protist, plant, and fungal affinities have all been entertained. The organisms have been better understood as improvements in microscopy facilitated the study of their fine structure, and there is mounting evidence to suggest that they represent either the eggs or juvenile stage of a marine animal.