Résumé:
This work is part of a morphometric study based on outline shape analysis by the transform of the
regular Fourier ellipses of the sea urchin Paracentrotus livides (Lamarck, 1816).
A sampling of 164 individuals was carried out at four stations on the coast of Mostaganem (Stidia,
Salamandre, Sidi Medjdoub and Sidi Lakhdar) by taking specimens of sea urchins from both
mediolittoral and infralittoral floors. Individuals were measured considering length without thorns
(L) and height (H). The "H / L" gibbosity was calculated to study the "station", "staging" and
"sexual dimorphism" effects of P. lividus individuals sampled on this parameter using the Kruskall-
Wallis test. Each individual was photographed in profile and in dorsal view in order to perform the
analysis of the contours of P. lividus test by the Fourier ellipses transform. The outlines were
standardized and analyzed to perform Principal Component Analysis (PCA) on the most relevant
contours.
The results showed that there were neither «station» effect nor "sexual dimorphism" effect of the
sampled P. lividus individuals. However, there is a "staging" effect between the mediolittoral and
infralittoral individuals on the H / L parameter of the sampled P. lividus individuals.
The results of the outline shape PCA showed that there is a morphometric disimilarity between the
individuals of both mediolittoral and infralittoral floors. Individuals in the mediolittoral stage have
contours that tend towards a circular and gibbous test with a convex form at thebase, in contrast to
individuals in the infralittoral stage that have outlines that tend towards a more flattened, oval and
concave test form.
This morpho-geometric method is not very expensive and could give results close to fastidious and
very expensive phylogenetic studies.
