As Members Of The Class Of Animals Called Vertebrates, Humans Have Which Characteristics?

Vertebrates

150 Chordates

Learning Objectives

By the end of this department, you will exist able to exercise the following:

• Describe the distinguishing characteristics of chordates
• Identify the derived characters of craniates that sets them apart from other chordates
• Describe the developmental fate of the notochord in vertebrates

Vertebrates are members of the kingdom Animalia and the phylum Chordata ((Figure)). Recall that animals that possess bilateral symmetry tin can be divided into two groups—protostomes and deuterostomes—based on their patterns of embryonic development. The deuterostomes, whose proper noun translates as "second oral cavity," consist of 2 major phyla: Echinodermata and Chordata. Echinoderms are invertebrate marine animals that have pentaradial symmetry and a spiny body covering, a group that includes sea stars, body of water urchins, and sea cucumbers. The nigh conspicuous and familiar members of Chordata are vertebrates, merely this phylum also includes 2 groups of invertebrate chordates.

Deuterostome phylogeny. All chordates are deuterostomes possessing a notochord at some stage of their life cycle.

Characteristics of Chordata

Animals in the phylum Chordata share v key chacteristics that announced at some stage during their development: a notochord, a dorsal hollow (tubular) nervus cord, pharyngeal gill arches or slits, a post-anal tail, and an endostyle/thyroid gland ((Effigy)). In some groups, some of these central chacteristics are present only during embryonic evolution.

The chordates are named for the notochord, which is a flexible, rod-shaped mesodermal construction that is institute in the embryonic stage of all chordates and in the developed 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 nervus cord, and provides rigid skeletal back up also as a flexible location for attachment of axial muscles. In some chordates, the notochord acts as the primary axial support of the body throughout the beast's lifetime. Nevertheless, in vertebrates (craniates), the notochord is nowadays only during embryonic development, at which time it induces the development of the neural tube and serves as a support for the developing embryonic torso. The notochord, nevertheless, is not found in the postembryonic stages of vertebrates; at this indicate, it has been replaced by the vertebral column (that is, the spine).

Visual Connection

Chordate features. In chordates, iv common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. The endostyle is embedded in the floor of the pharynx.

Which of the following statements about mutual features of chordates is truthful?

1. The dorsal hollow nervus cord is role of the chordate fundamental nervous system.
2. In vertebrate fishes, the pharyngeal slits become the gills.
3. Humans are not chordates considering humans do not take a tail.
4. Vertebrates practice not have a notochord at any point in their development; instead, they have a vertebral cavalcade.
5. The endostyle secretes steroid hormones.

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The dorsal hollow nerve cord is derived from ectoderm that rolls into a hollow tube during development. In chordates, it is located dorsally to the notochord. In contrast, the nervous organization 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 encephalon and spinal cord, which together comprise the central nervous organisation (CNS). The peripheral nervous organisation (PNS) refers to the peripheral nerves (including the cranial fretfulness) 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 exterior environs. In organisms that live in aquatic environments, pharyngeal slits allow for the exit of water that enters the mouth during feeding. Some invertebrate chordates use the pharyngeal slits to filter food out of the h2o that enters the oral cavity. The endostyle is a strip of ciliated mucus-producing tissue in the flooring of the throat. Nutrient particles trapped in the mucus are moved along the endostyle toward the gut. The endostyle too 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 curvation, with the second arch becoming the hyoid and jaw support.

The postal service-anal tail is a posterior elongation of the body, extending across 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 balance, courtship, and signaling when danger is near. In humans and other great apes, the post-anal tail is reduced to a vestigial coccyx ("tail bone") that aids in balance during sitting.

Link to Learning

Click for a video discussing the development of chordates and 5 characteristics that they share.

Chordates and the Development of Vertebrates

2 clades of chordates are invertebrates: Cephalochordata and Urochordata. Members of these groups likewise possess the five distinctive features of chordates at some betoken during their development.

Cephalochordata

Members of Cephalochordata possess a notochord, dorsal hollow tubular nervus cord, pharyngeal slits, endostyle/thyroid gland, and a post-anal tail in the adult stage ((Effigy)). The notochord extends into the head, which gives the subphylum its name. Although the neural tube likewise extends into the caput region, there is no well-defined brain, and the nervous organisation is centered around a hollow nerve cord lying higher up the notochord. Extinct members of this subphylum include Pikaia, which is the oldest known cephalochordate. Excellently preserved Pikaia fossils were recovered from the Burgess shales of Canada and date to the centre of the Cambrian age, making them more than 500 million years old. Its anatomy of Pikaia closely resembles that of the extant lancelet in the genus Branchiostoma.

The lancelets are named for their bladelike shape. Lancelets are only a few centimeters long and are commonly found buried in sand at the lesser of warm temperate and tropical seas. Cephalochordates are suspension feeders. A water current is created by cilia in the mouth, and is filtered through oral tentacles. H2o from the mouth then enters the pharyngeal slits, which filter out food particles. The filtered h2o collects in a gill chamber chosen the atrium and exits through the atriopore. Trapped food particles are caught in a stream of mucus produced past the endostyle in a ventral ciliated fold (or groove) of the pharynx and carried to the gut. Most gas commutation occurs across the body surface. Sexes are split up and gametes are released into the h2o through the atriopore for external fertilization.

Cephalochordate anatomy. In the lancelet and other cephalochordates, the notochord extends into the head region. Adult lancelets retain all v key characteristics of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.

Urochordata

The 1,600 species of Urochordata are as well known as tunicates ((Figure)). The name tunicate derives from the cellulose-similar carbohydrate material, called the tunic, which covers the outer body of tunicates. Although tunicates are classified equally chordates, the adults exercise not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do accept pharyngeal slits and an endostyle. The "tadpole" larval form, even so, possesses all five structures. Nearly tunicates are hermaphrodites; their larvae hatch from eggs inside the adult tunicate'southward body. After hatching, a tunicate larva (possessing all five chordate features) swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. It so attaches via the head to the surface and undergoes metamorphosis into the developed form, at which point the notochord, nerve cord, and tail disappear, leaving the pharyngeal gill slits and the endostyle as the ii remaining features of its chordate morphology.

Urochordate anatomy. (a) This photograph shows a colony of the tunicate Botrylloides violaceus. (b) The larval stage of the tunicate possesses all of the features feature of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a mail service-anal tail. (c) In the adult phase, the notochord, nerve string, and tail disappear, leaving but the pharyngeal slits and endostyle. (credit: modification of work past Dann Blackwood, USGS)

Adult tunicates may be either solitary or colonial forms, and some species may reproduce by budding. Most tunicates alive a sessile being on the ocean floor and are suspension feeders. Yet, chains of thaliacean tunicates chosen salps ((Figure)) can swim actively while feeding, propelling themselves equally they motion water through the pharyngeal slits. The primary foods of tunicates are plankton and detritus. Seawater enters the tunicate'south body through its incurrent siphon. Suspended cloth is filtered out of this water by a mucous net produced past the endostyle and is passed into the intestine via the activity of cilia. The anus empties into the excurrent siphon, which expels wastes and h2o. Tunicates are found in shallow body of water waters around the world.

Salps. These colonial tunicates feed on phytoplankton. Salps are sequential hermaphrodites, with younger female colonies fertilized by older male colonies. (credit: Oregon Department of Fish & Wildlife via Wikimedia Commons)

Subphylum Vertebrata (Craniata)

A cranium is a bony, cartilaginous, or fibrous structure surrounding the encephalon, jaw, and facial bones ((Figure)). Most bilaterally symmetrical animals take a head; of these, those that accept a cranium incorporate the clade Craniata/Vertebrata, which includes the primitively jawless Myxini (hagfishes), Petromyzontida (lampreys), and all of the organisms called "vertebrates." (Nosotros should annotation that the Myxini have a cranium but lack a courage.)

A craniate skull. The subphylum Craniata (or Vertebrata), including this placoderm fish (Dunkleosteus sp.), are characterized by the presence of a cranium, mandible, and other facial basic. (credit: "Steveoc 86"/Wikimedia Eatables)

Members of the phylum Craniata/Vertebrata display the five characteristic features of the chordates; notwithstanding, members of this group also share derived characteristics that distinguish them from invertebrate chordates. Vertebrates are named for the vertebral column, composed of vertebrae—a series of carve up, irregularly shaped bones joined together to class a backbone ((Figure)). Initially, the vertebrae grade in segments around the embryonic notochord, but eventually supplant it in adults. In most derived vertebrates, the notochord becomes the nucleus pulposus of the intervertebral discs that absorber and back up adjacent vertebrae.

A vertebrate skeleton. Vertebrata are characterized by the presence of a backbone, such as the one that runs through the centre of this fish. All vertebrates are in the Craniata clade and have a attic. (credit: Ernest 5. More; taken at Smithsonian Museum of Natural History, Washington, D.C.)

The human relationship of the vertebrates to the invertebrate chordates has been a matter of contention, but although these cladistic relationships are still being examined, it appears that the Craniata/Vertebrata are a monophyletic group that shares the 5 basic chordate characteristics with the other ii subphyla, Urochordata and Cephalochordata. Traditional phylogenies identify the cephalochordates as a sis clade to the chordates, a view that has been supported by about electric current molecular analyses. This hypothesis is further supported by the discovery of a fossil in China from the genus Haikouella. This organism seems to be an intermediate form betwixt cephalochordates and vertebrates. The Haikouella fossils are about 530 one thousand thousand years quondam and appear similar to modernistic lancelets. These organisms had a encephalon and eyes, as practise vertebrates, but lack the skull found in craniates. ¹ This evidence suggests that vertebrates arose during the Cambrian explosion.

Vertebrates are the largest grouping of chordates, with more 62,000 living species, which are grouped based on anatomical and physiological traits. More than one nomenclature and naming scheme is used for these animals. Here we will consider the traditional groups Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia, which constitute classes in the subphylum Vertebrata/Craniata. About all modern cladists classify birds within Reptilia, which correctly reflects their evolutionary heritage. Thus, nosotros now have the nonavian reptiles and the avian reptiles in our reptilian classification. We consider them separately simply for convenience. Further, we will consider hagfishes and lampreys together as jawless fishes, the Agnatha, although emerging classification schemes separate them into chordate jawless fishes (the hagfishes) and vertebrate jawless fishes (the lampreys).

Animals that possess jaws are known equally gnathostomes, which ways "jawed mouth." Gnathostomes include fishes and tetrapods. Tetrapod literally means "four-footed," which refers to the phylogenetic history of various land vertebrates, fifty-fifty though in some of the tetrapods, the limbs may have been modified for purposes other than walking. Tetrapods include amphibians, reptiles, birds, and mammals, and technically could too refer to the extinct fishlike groups that gave rise to the tetrapods. Tetrapods tin be further divided into two groups: amphibians and amniotes. Amniotes are animals whose eggs contain four extraembryonic membranes (yolk sac, amnion, chorion, and allantois) that provide diet and a h2o-retaining surround for their embryos. Amniotes are adjusted for terrestrial living, and include mammals, reptiles, and birds.

Section Summary

The five characteristic features of chordates present during some fourth dimension of their life cycles are a notochord, a dorsal hollow tubular nerve cord, pharyngeal slits, endostyle/thyroid gland, and a mail-anal tail. Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets), together with the vertebrates in the Vertebrata/Craniata. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms. Most tunicates alive on the ocean floor and are suspension feeders. Which of the two invertebrate chordate clades is more closely related to the vertebrates continues to exist debated. Vertebrata is named for the vertebral column, which is a feature of most all members of this clade. The name Craniata (organisms with a attic) is considered to be synonymous with Vertebrata.

Visual Connectedness Questions

(Figure) Which of the post-obit statements nigh common features of chordates is truthful?

1. The dorsal hollow nerve cord is part of the chordate fundamental nervous organization.
2. In vertebrate fishes, the pharyngeal slits get the gills.
3. Humans are not chordates because humans do not accept a tail.
4. Vertebrates practise not have a notochord at any point in their development; instead, they have a vertebral column.

(Figure) A

Review Questions

Which of the following is non independent in phylum Chordata?

1. Cephalochordata
2. Echinodermata
3. Urochordata
4. Vertebrata

B

Which group of invertebrates is nigh closely related to vertebrates?

1. cephalochordates
2. echinoderms
3. arthropods
4. urochordates

A

Hagfish, lampreys, sharks, and tuna are all chordates that tin also be classified into which group?

1. Craniates
2. Vertebrates
3. Cartilaginous fish
4. Cephalocordata

A

Critical Thinking Questions

What are the characteristic features of the chordates?

The characteristic features of the phylum Chordata are a notochord, a dorsal hollow nervus cord, pharyngeal slits, and a post-anal tail.

What is the structural advantage of the notochord in the human embryo? Be certain to compare the notochord with the respective structure in adults.

The notochord is a flexible structure that provides support for the embryo'due south torso and germination of the neural tube. In the adults, the notochord has been replaced by the bony, rigid vertebral column. This loss of flexibility restricts the motility of adult humans, and would get in unlikely that the embryo would fit inside the small space it is allotted inside the uterus.

Footnotes

• ane Chen, J. Y., Huang, D. Y., and Li, C. W., "An early Cambrian craniate-like chordate," Nature 402 (1999): 518–522, doi:ten.1038/990080.

Glossary

Cephalochordata

chordate clade whose members possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage

Chordata

phylum of animals distinguished past their possession of a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a mail-anal tail at some point during their development

Craniata

clade composed of chordates that possess a cranium; includes Vertebrata together with hagfishes

cranium

bony, cartilaginous, or fibrous structure surrounding the encephalon, jaw, and facial bones

dorsal hollow nerve cord

hollow, tubular structure derived from ectoderm, which is located dorsal to the notochord in chordates

lancelet

member of Cephalochordata; named for its blade-like shape

notochord

flexible, rod-shaped back up structure that is found in the embryonic phase of all chordates and in the adult stage of some chordates

pharyngeal slit

opening in the pharynx

post-anal tail

muscular, posterior elongation of the body extending beyond the anus in chordates

tetrapod

phylogenetic reference to an organism with a 4-footed evolutionary history; includes amphibians, reptiles, birds, and mammals

tunicate

sessile chordate that is a member of Urochordata

Urochordata

clade composed of tunicates

vertebral column

serial of separate bones joined together as a backbone

Vertebrata

members of the phylum Chordata that possess a courage

Source: https://opentextbc.ca/biology2eopenstax/chapter/chordates/

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