What Is One Characteristic That Separates Chordates From All Other Animals?

Learning Outcomes

Describe the distinguishing characteristics of chordates

Vertebrates are members of the kingdom Animalia and the phylum Chordata (Figure 1). The vertebrates showroom 2 major innovations in their development from the invertebrate chordates. These innovations may be associated with the whole genome duplications that resulted in a quadruplication of the basic chordate genome, including theHox gene loci that regulate the placement of structures along the three axes of the body. Ane of the first major steps was the emergence of the quadrupeds in the course of the amphibians. A second step was the development 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. Within the amniotes, modifications of keratinous epidermal structures take given rise to scales, claws, hair, and feathers. The scales of reptiles sealed their skins against water loss, while hair and feathers provided insulation to support the evolution of endothermy, too every bit served other functions such as camouflage and mate attraction in the vertebrate lineages that led to birds and mammals.

Figure 1. All chordates are deuterostomes possessing a notochord.

Characteristics of Chordata

Animals in the phylum Chordata share five key chacteristics that appear at some phase during their development: a notochord, a dorsal hollow (tubular) nerve string, pharyngeal gill arches or slits, a mail-anal tail, and an endostyle/thyroid gland (Figure 2). In some groups, some of these central chacteristics are present only during embryonic development.

The chordates are named for the notochord , which is a flexible, rod-shaped mesodermal structure that is constitute in the embryonic stage of all chordates and in the adult stage of some chordate species. It is strengthened with glycoproteins similar to cartilage and covered with a collagenous sheath. The notocord is located between the digestive tube and the nerve string, and provides rigid skeletal support likewise as a flexible location for attachment of axial muscles. In some chordates, the notochord acts as the primary axial support of the trunk throughout the animal'south lifetime. However, in vertebrates (craniates), the notochord is present simply during embryonic evolution, at which time it induces the development of the neural tube and serves as a support for the developing embryonic trunk. The notochord, nonetheless, is not found in the postembryonic stages of vertebrates; at this bespeak, information technology has been replaced past the vertebral cavalcade (that is, the spine).

The illustration shows a fish-shaped chordate. A long, thin dorsal hollow nerve cord runs the length of the chordate, along the top. Immediately beneath the nerve cord is a notochord that also runs the length of the organism. Beneath the notochord, pharyngeal slits cut diagonally into tissue toward the front of the organism. A post-anal tail occurs at the rear.

Effigy 2. In chordates, four common features appear at some indicate during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a mail-anal tail.

Practice Question

Which of the following statements about common features of chordates is true?

The dorsal hollow nerve cord is role of the chordate cardinal nervous system.
In vertebrate fishes, the pharyngeal slits become the gills.
Humans are not chordates because humans do not have a tail.
Vertebrates do not have a notochord at whatever betoken in their development; instead, they accept a vertebral column.

Testify Answer

Argument a is true.

The dorsal hollow nerve stringis derived from ectoderm that rolls into a hollow tube during evolution. In chordates, information technology is located dorsally to the notochord. In dissimilarity, the nervous organisation in protostome animal phyla is characterized by solid nerve cords that are located either ventrally and/or laterally to the gut. In vertebrates, the neural tube develops into the brain and spinal cord, which together comprise the cardinal nervous organisation (CNS). The peripheral nervous organization (PNS) refers to the peripheral fretfulness (including the cranial nerves) lying outside of the brain and spinal cord.

Pharyngeal slits are openings in the throat (the region just posterior to the mouth) that extend to the outside environment. In organisms that live in aquatic environments, pharyngeal slits allow for the exit of water that enters the mouth during feeding. Some invertebrate chordates apply the pharyngeal slits to filter food out of the water that enters the mouth. The endostyle is a strip of ciliated mucus-producing tissue in the flooring of the pharynx. Food particles trapped in the mucus are moved along the endostyle toward the gut. The endostyle also produces substances similar to thyroid hormones and is homologous with the thyroid gland in vertebrates. In vertebrate fishes, the pharyngeal slits are modified into gill supports, and in jawed fishes, into jaw supports. In tetrapods (land vertebrates), the slits are highly modified into components of the ear, and tonsils and thymus glands. In other vertebrates, pharyngeal arches, derived from all three germ layers, give ascension to the oral jaw from the get-go pharyngeal arch, with the second arch becoming the hyoid and jaw support.

The post-anal tail is a posterior elongation of the trunk, extending beyond the anus. The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species, such equally fishes. In some terrestrial vertebrates, the tail also helps with residue, courtship, and signaling when danger is virtually. In humans and other great apes, the post-anal tail is reduced to a vestigial coccyx ("tail bone") that aids in balance during sitting.

Sentry this video discussing the evolution of chordates and five characteristics that they share.