Echinoderms and Hemichordates

Abstract

In the first half of the 19th century, the publications of two Frenchmen, Jean-Baptiste de Monet, Chevalier de Lamarck and Baron Léopold Chrétien Fréderic Dagobert Cuvier (known as Georges), were generally accepted as standard works on systematic zoology. They disagreed on evolution (Cuvier rejected the idea), but they agreed on the placement of the Echinodermata in the Radiata, along with medusae and corals. Echinoderms have little in common with other radial animals except the form of symmetry, and, in the middle of the century, Frey and Leuckart (1847) and Leuckart (1854) pointed out that echinoderms, with three distinct body layers and a well developed body cavity, were at a ‘higher’ grade of organization than medusae and other coelenterates, with only two layers and no coelom. Embryological studies on a number of groups enabled Huxley (1875) to associate the Echinodermata with the Chaeto-gnatha and Enteropneusta as enterocoelous deuterostomes, and this link was reinforced when Metchnikoff (1881) drew attention to the resemblances between the larvae of echinoderms and enteropneusts.