Wirtz, P.; Diesel, R.: The social structure of Inachus phalangium, a spider crab associated with the sea anemone Anemonia sulcata. Zeitschrift für Tierspychologie 62 (3), pp. 209 - 234 (1983)
Scientists studying a rare population of tool-using chimpanzees have found that aging can have a profound impact on their abilities—but not all chimps decline equally.