These classes are distinguished by traits such as the

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the Echinodermata are; Ophiuroidea, Crinoidea, Echinoidea, Holothuroidea, and Asteroidea. These classes are distinguished by traits such as the presence of tube feet, spiny protective skin, multiple arms, and suckers. Finally, with the development of the notochord, the phylum, Chordata, is introduced. The phylum, Chordata, includes two groups of invertebrates, Urochordata and Cephlochordata, and vertebrates. The trait that distinguishes the two groups of
Vinay Jithendran BIO 112-542 Lab invertebrates, Urochordata and Cephlochordata, are the presence of muscle segmentation in Cephlochordata organisms. The trait that distinguishes the invertebrates from the vertebrates is the presences of a vertebrae and cartilage in vertebrates. The subphylum, Vertebrates, consists of multiple classes which are; Myxini, Petromyzontida, Chondrichthyes, Actinoptergyii, Sacroptergyii, Amphibia, Mammalia, and Reptilia. The classes, Myxini and Petromyzontida, are distinguished by being cyclostomes. Cyclostomes lack mineralized teeth but have analogous structures made of the protein keratin. 2 The development of hinged jaws, introduced the Gnathostome classes starting with, Chondrichthyes and Actinoptergyii. Next, the development of lungs, introduced the classes, Sacroptergyii and Amphibia. Finally, the development of the amniotic egg and the 4-chambered heart, progressed into the growth of the classes, Mammalia and Reptilia. These classes can be distinguished by the presence of hair and mammary glands in mammals, and the presence of feathers (birds) and diapsid skulls in reptiles. That concludes the evolutionary trend from the modern collared flagellate, choanoflagellate, to the phylum, Chordata. 2 Harris-Haller, T. 2014. Laboratory Manual for Biology 112 , 8 th ed. Chapter 7, Hayden-McNeil Publishing.

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