![]() All chordates are deuterostomes possessing a notochord at some stage of their life cycle. The most conspicuous and familiar members of Chordata are vertebrates, but this phylum also includes two groups of invertebrate chordates.įigure 29.2 Deuterostome phylogeny. Echinoderms are invertebrate marine animals that have pentaradial symmetry and a spiny body covering, a group that includes sea stars, sea urchins, and sea cucumbers. The deuterostomes, whose name translates as “second mouth,” consist of two major phyla: Echinodermata and Chordata. Recall that animals that possess bilateral symmetry can be divided into two groups-protostomes and deuterostomes-based on their patterns of embryonic development. ![]() Vertebrates are members of the kingdom Animalia and the phylum Chordata ( Figure 29.2). For example, the Biodiversity Action Plan is an international program, ratified by 188 countries, which is designed to protect species and habitats. Attempts are being made around the world to prevent the extinction of threatened species. Amphibians and mammals are the classes with the greatest percentage of threatened species, with 29 percent of all amphibians and 21 percent of all mammals classified as threatened. According to the International Union for the Conservation of Nature, more than 6,000 vertebrate species are classified as threatened. The scales of reptiles sealed their skins against water loss, while hair and feathers provided insulation to support the evolution of endothermy, as well as served other functions such as camouflage and mate attraction in the vertebrate lineages that led to birds and mammals.Ĭurrently, a number of vertebrate species face extinction primarily due to habitat loss and pollution. Within the amniotes, modifications of keratinous epidermal structures have given rise to scales, claws, hair, and feathers. A second step was the evolution of the amniotic egg, which, similar to the evolution of pollen and seeds in plants, freed terrestrial animals from their dependence on water for fertilization and embryonic development. One of the first major steps was the emergence of the quadrupeds in the form of the amphibians. These innovations may be associated with the whole genome duplications that resulted in a quadruplication of the basic chordate genome, including the Hox gene loci that regulate the placement of structures along the three axes of the body. The vertebrates exhibit two major innovations in their evolution from the invertebrate chordates. Describe the developmental fate of the notochord in vertebrates.Identify the derived characters of craniates that sets them apart from other chordates.Describe the distinguishing characteristics of chordates.By the end of this section, you will be able to do the following:
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