The Pea Aphid (Acyrthosiphon pisum) life cycle:
During the summer months, asexual females give live birth to clonal offspring (see photo). These offspring undergo 4 molts during larval development to become (A) unwinged or (B) winged asexually reproducing adults. Winged individuals are induced by crowding or stress during either prenatal or early larval stages; they are more able to disperse to colonize a new plant. After repeated cycles of asexual reproduction with generation time of about 10 days, shorter autumn day lengths trigger the production of (C) unwinged sexual females and (D) males, which can be winged or unwinged in pea aphids, depending on genotype.After mating, sexual females deposit (E) overwintering eggs, which hatch in the spring to produce (F) wingless, asexual foundress females. In some populations, especially in locations without a cold winter, the sexual and egg-producing portions of the life cycle are eliminated, leading to continuous cycles of asexual reproduction.
Horseshoe Crab and Crayfish, Triassic France by Douglas Henderson
“illustration for the book DAWN OF THE DINOSAURS, LIFE IN THE TRIASSIC (…) The image represents brackish pool deposits from the Gres a Voltzia Formation near the early Atlantic shore of Triassic France some 230 million years ago. Trapped in a transient pool are fragments of shore plants and various conifer limbs, leaves and a cone, together with the small fish Dipteronotus, a small crayfish, a horseshoe crab and numerous small jellyfish.”
Artist: E. Naylor and P.J. Llewellyn
Naylor, E. (1972). British Marine Isopods. New York: Academic Press Inc.