Polymorphism of colour patterns related to environmental factors: correlation between habitat, sight, and mimicry in sirpus zariquieyi gordon, 1953

Colour patterns of the shallow-water crab, Sirpus zariquieyi, a Mediterranean species, are formed by chromatophores located beneath the translucent cuticle, around internal organs, and in muscular tissues. The variation in the colours and patterns on the carapace is correlated with the area of occurrence. The colours themselves and the presence of, e.g., spots, and their number and arrangement, are all clearly related to the habitat in which the specimens are found. This apparently holds true irrespective of the size of individuals, and consequently of their age, in contrast to findings in other crabs, which have been demonstrated to show chromatic variability according to their juvenile stage, whereas adults show a coloration almost as uniform as the substrate they inhabit. This is probably because there is an insignificant difference in size between juvenile and adult Sirpus zariquieyi and this in turn may be correlated with the fact that the habitat is the same for both juveniles and adults. Specimens of Sirpus have been studied and it is confirmed that disruptive colouring of the exoskeleton is linked to individuals that live in habitats where the most frequent form of camouflage for amphipods, crabs, gastropods, isopods, shrimp, and other macroinvertebrates, consists of coloured spots, in the same way as for small fry (Pisces, Gobioesocidae). All these animals live on Posidonia oceanica leaves as well as on rocky bottoms rich in green, brown, and red algae, encrusted sponges, and other macro-invertebrates, such as bryozoans. /// I disegni a colori del granchio Sirpus zariquieyi, specie litorale del Mar Mediterraneo, sono formati da cromatofori localizzati sotto la cuticola dell'esoscheletro, semitrasparente, attorno agli organi interni e nei tessuti muscolari. Il motivo della variazione dei colori e dei disegni presenti sul carapace deve essere ricercato nelle differenti aree in cui i granchi vivono. La correlazione tra colori, macchie, il loro numero e la loro disposizione in relazione all'habitat nel quale i granchi sono stati presi è chiara in tutti gli esemplari catturati. Questo accade a prescindere dalle dimensioni degli individui e di conseguenza dallo stadio giovanile ed adulto, contrariamente a quanto osservato in altre specie di granchi che hanno mostrato una variabilità cromatica e disegni caratteristici nello stadio giovanile, legati all'ambiente di vita, mentre gli adulti presentano un colore quasi uniforme adattato all'ambiente di vita d