At the moment, I only have only provided a very brief introduction to the Chitinozoa, but as time permits, I will update the information to build a comprehensive resource, with links to other sites of relevance.
 

Group: Chitinozoa
Chitinozoans are organic-walled microfossils of uncertain origin. They are composed of 'pseudochitin', a very resistant organic compound that allows for excellent preservation, and recovery using the strongest acid digestion techniques.

The group is entirely Palaeozoic, with a span of some 120 million years, from the earliest Ordovician to the latest Devonian.  They are found only in marine sediments, and are especially abundant in black shales, although excellent 3-D preservation has been found in carbonates.

Chitinozoans themselves are of uncertain origin: the most accepted hypothesis is that they are the eggs of soft-bodied metazoans, but more than that is not known at present.

Due to their abundance and diversity in Palaeozoic strata, chitinozoans make an excellent biostratigraphical fossil.  Detailed biozonal schemes have been erected for many parts of the Palaeozoic, with current research (such as my own!) constantly expanding and integrating the available data.  Due to their recognition as a valuable biostratigraphical tool, chitinozoans have become of interest to the hydrocarbon exploration industry, and Palaeozoic source rocks account for a large proportion of the world's oil and gas reserves.

Chitinozoan taxa are differentiated upon their morphological characteristics, such as shape, ornamentation, and appendages/processes, and there are over 1,000 species in 56 genera to date: they have also been found on every continent.  An excellent review of chitinozoan classification was published by Paris et al. (1999), and is well worth obtaining for anyone interested in the group.

Professors Florentin Paris and Jacques Verniers (both world-renowned chitinozoan experts) provide another excellent, well-illustrated introduction to chitinozoans in the microfossils section of the new 'Encyclopaedia of Geology' published by Elsevier (reference below).

The CIMP (Commission Internationale de Microflore du Paléozoïque) Subcommission on Chitinozoans has an established website with many links and resources, and are the main international forum for chitinozoan research.  The next meeting of the CIMP is in September 2006, in the Czech Republic: details can be found here.
 

Further reading:

PARIS, F., GRAHN, Y., NESTOR, V. and LAKOVA, I. 1999.  A revised chitinozoan classification.  Journal of Paleontology, 73, 549–570.

PARIS, F. and VERNIERS, J.  2005.  Chitinozoa.  In SELLEY, R.C., COCKS, L. R. M. and PLIMER, I. R. (eds).  Encylcopedia of Geology: Volume Three.  Elsevier Academic Press, 428–440.