Eyestalk length, internal eye structure, pigmented eye area, and pigments in eyes and exoskeleton were studied in two stygobiont crayfish, Procambarus cavernicola and Procambarus oaxacae reddelli. Results were compared with the epigeal crayfish Procambarus olmecorum, all three species inhabiting the karstic region of Acatlan, Oaxaca, Mexico. The stygobite species have shorter eyestalks and reduced pigmented areas compared with the epigeal species. For both eye and integument pigments, the stygobite species have a reduction in their total absorbance spectra compared to the epigeal species. Internal eye structure and organisation are reduced in both stygobite species, but to a greater extent in Procambarus cavernicola. These results are discussed in relation to the time of cave colonisation, the degree of adaptation, and the energy economy hypothesis.
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Vol. 25 • No. 3