Introduction

Red coralline algae (Corallinales) are characterized by a slow morphogenetical growth and by the deposition of calcium carbonate within the cell walls. The anatomical and cytological structure of these algae enables the corallines to colonize various common substrates of different nature, they can be encrusting on hard bottoms, on shells; erect, geniculate; free-living (e.g.: mäerl, rhodoliths), sub-spherical or semi-endophytic on other corallines.
The Corallinales are distributed worldwide within the photic zone (Steneck 1986): from warm regions (tropical - temperate) to the cold ones (arctic - subarctic) ranging from present time living forms to fossil Tertiary (Oligocene) thalli with a relatively long history on Earth. Therefore, on the basis of their perennial nature, the Corallinales must be considered important landmarks for phytogeographical approaches (Kurt et al. 2009) as well as for long term climate studies. These algae have an essential role in the submarine ecosystems, i.e as palaeomarkers they provide substantial detailed information about middle and long term environmental changes, as recognized by a rich scientific literature. An example among the others (Basso, 1998) is the influence of hydrodynamism which through adaptive processes may affect the morphology of thalli as a result of the degree of the energy of water motion.
To refer to bio-indicators as complete, it is necessary to study well-characterized species, in a presence/absence, cause/effect relation caused by well-defined phenomena. A thorough identification is therefore highly recommended.
On the contrary due to the technical-morphological limits and identification difficulties in many floristic studies Corallinales have been referred to as non-identified corallines, “coralline algal nodules”, “coralloid growth”, “lithothamnion balls”, etc.
It is not rare in fact that different phenomena such as polymorphism (intraspecific variability), morphological convergence (infraspecific variability), morphometric ranges are frequent often making precise identification particularly difficult or impossible. The absence/paucity of diacritic clearly reliable taxonomical characters makes such difficulties more relevant.

The reasons for a choice

The aim of the present work is to provide identification tools which lead to the determination of the species by means of two different processes with diverse but complementary scopes: one is the “Atlas-Glossary” and the other is the “Identi-Key”.
The first identification key (“Atlas-Glossary”) has the typical structure of a dichotomous key offering a fixed sequence of different steps (Single Access Key-SAK) the choice of which leads to the next step ranging from general features to more particular ones with a closed arrangement and with the presence of at least one diagnostic character.
The second key (“Identi-Key”) has an open structure where the user can make multiple choices in any order from a set of different characters (Multiple Access Key – MAK) similar to a real random access key. Like in an Identikit the identification is the result of a combined mix of information (polythetic key).
On one hand the choice of developing an “Atlas-Glossary” has been made to provide an image-glossary not only as an accessory but as an instrument fostering language learning and therefore gathering educational purposes during and through the choice of diagnostic characters (Bressan & Babbini, 2003).
Here an empirical approach model is proposed where the order of analysis of taxonomical diagnostic characters ranged from macro-morphological ones (mostly phenotypic, external and more variable) to microscopic, anatomo- cytological ones more constant thus more reliable.
The “IdentiKey” has been developed not only for neophytes but also for users searching for precise and ready to use instrument, with an easy interface for the identification of the Corallinales of the Mediterranean Sea.