8. Deuterostomes I: starfish, sea squirts, and amphioxus

Abstract

‘Deuterostomes I: starfish, sea squirts, and amphioxus’ is concerned with some of the phyla of the Deuterostomia superphylum — the Echinodermata, Hemichordata, and the Chordata subphyla tunicates and amphioxus. The five classes of echinoderms — starfish, sea urchins, brittlestars, sea cucumbers, and sea lilies — have much in common with each other, but little with anything else. They display five-fold, or pentaradial, symmetry that has evolved from bilateral symmetry. Acorn worms and pterobranchs, part of the Hemichordata phylum, are described. The chordates can be split into three evolutionary groups, or subphyla — tunicates (such as sea squirts and larvaceans), vertebrates, and a group of marine chordates called cephalochordates, more usually referred to as amphioxus.