Question

10.a. Describe the differences between the terms in each of the following pairs. (i) Coelomate versus acoelomate body plan (ii) Protostome versus deuterostome development (ii)Radial versus bilateral symmetry (b) Explain how each of these pair of features was important in constructing the phylogenetic tree shown below. Use specific examples from the tree in your discussion. 24-10 20 11.1 11.The two phylogenetic trees shown on the next page represent the relationship of whales to six other mammals. All of the organisms shown have a pulley-shaped astragalus bone in the ankle except for the whale. a. For each tree, describe a monophyletic group, the closest relative to the whale, and the point at which the pulley astragalus bone was lost or gained. b. Based on the principle of parsimony (the simplest explanation is the best) and the genomic information in the table shown, identify which tree is the best representation of the evolutionary relationship of these animals, and justify your answer. Chordata Arthropoda Echinodermata Nematoda Platyhelminthes Cnidaria Porifera

Answer 1

10. a. i. Coelomates have true body cavity called coelom while acoelomates do not have body cavity. Chordates are coelomates. Tapeworms, flatworms are acoelomates.

ii. Protostomes and deuterostomes can be differentiated on the basis of their development in the early embryonic stage. In protostomes , firstly blastopore develops into mouth and then forms anus, while in deuterostomes, blastopore develops into anus and then other opening forms mouth. Protostomes are invertebrates like flatworms while chordates are deuterostomes.

iii. In radial symmetry, body is divided into equal parts around the central axis of the body, example starfish. While in bilateral symmetry body can be divided into left and right equal halves, example human.

b. Porifera and cnidaria have no proper tissues. Porifera, Cnidaria and platyhelminthes are all acolemates. While rotifer and nemtaodes are pseudocolemates , that is they have false body cavity. Above the nematodes are all coelomates. Platyhelminthes, rotifera, nematode, annelida, mollusca, and arthropoda are all on one side of the tree and they are protostomes, while echinodermata and chordate on the other side are deuterostomes. In deuterostomes, echinodermata have radial symmetry while chordates show bilateral symmetry.