Pentameral symmetry is the major form and the other forms are derived from it. Log in. Terms in this set (38) What is a chordate? Secondary School. How is it possible that a species evolved into animals as different as starfish and people? Chordates are eucoelomate deuterostomes, and probably share a common ancestor with echinoderms. How do we know that chordates share a most common ancestor with echinoderms? The principal reason we consider tunicates (sea squirts) similar to the ancestor of all chordates is that a. the body plan of adult tunicates parallels that of chordates. That makes the marine origin of chordates more plausible. The echinoderms have a radially arranged, pentamerous body structure that is very different from the bilateral body structure of the related deuterostome phyla, the hemichordates and the chordates. Chordate - Chordate - Evolution and paleontology: Many scientists maintain that chordates originated sometime earlier than 590 million years ago; that is, they predate the fossil record. Chordates share a most common ancestor with echinoderms. Ancestry and Evolution Since the mid-nineteenth century when the theory of organic evolution became the focal point for ferreting out relationships among groups of living organisms, zoologists have debated the question of chordate origins. Spell. According to cladogram, Echinoderms are the organisms which are closest relative to chordates. Such early representatives were soft-bodied and therefore left a poor fossil record. Explanation: It is proved that Echinoderms and chordates are from common ancestral origin. Write. Which of the following statements about common features of chordates is true? c. tunicates have a lophophore-style mouth. 23. Noto chord at same point of life cycle. Gravity. Join now. The anatomy of a cephalochordate shown here illustrates all of these features. Join now. (The phylogenetic tree shown above represents the evolutionary relationships between the major clades of chordates. PLAY. The neural crest would have existed in the latest common ancestor of extant chordates, or even earlier. Three important characteristics unite the Phylum Chordata. Bio Chapter 26. The main difference between echinoderms and chordates is that the echinoderms have a mesodermal skeleton made up of calcite known as ossicles whereas chordates have an internal skeleton made up of bones and cartilages. nfarkhan. Match. Flashcards. However, the ancestors of echinoderms, which originated from Cambrian period, were believed to be bilaterians.Echinoderm larvae are bilateral during their early development.