Which Of The Following Sets Of Animals Contains Only Gnathostomes?

Vertebrates

150 Chordates

Learning Objectives

By the end of this section, y'all will exist able to do the following:

• Depict the distinguishing characteristics of chordates
• Identify the derived characters of craniates that sets them apart from other chordates
• Draw 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 every bit "second oral fissure," consist of two major phyla: Echinodermata and Chordata. Echinoderms are invertebrate marine animals that have pentaradial symmetry and a spiny trunk roofing, a group that includes sea stars, sea urchins, and sea cucumbers. The almost conspicuous and familiar members of Chordata are vertebrates, but this phylum besides 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 five primal chacteristics that appear at some stage during their development: a notochord, a dorsal hollow (tubular) nerve cord, pharyngeal gill arches or slits, a mail service-anal tail, and an endostyle/thyroid gland ((Figure)). In some groups, some of these central chacteristics are nowadays just during embryonic development.

The chordates are named for the notochord, which is a flexible, rod-shaped mesodermal structure that is institute in the embryonic phase 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 nerve string, and provides rigid skeletal support also equally a flexible location for attachment of axial muscles. In some chordates, the notochord acts as the main centric back up of the body throughout the fauna'southward lifetime. However, in vertebrates (craniates), the notochord is present only during embryonic evolution, at which time it induces the evolution of the neural tube and serves every bit a support for the developing embryonic torso. The notochord, all the same, is not institute in the postembryonic stages of vertebrates; at this betoken, information technology 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 nervus cord, pharyngeal slits, and a mail service-anal tail. The endostyle is embedded in the flooring of the pharynx.

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

1. The dorsal hollow nerve cord is part of the chordate central nervous system.
2. In vertebrate fishes, the pharyngeal slits become the gills.
3. Humans are not chordates because humans do not have a tail.
4. Vertebrates do not have a notochord at any bespeak in their development; instead, they have a vertebral column.
5. The endostyle secretes steroid hormones.

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The dorsal hollow nervus string is derived from ectoderm that rolls into a hollow tube during evolution. In chordates, information technology is located dorsally to the notochord. In contrast, the nervous system in protostome animal phyla is characterized by solid nervus 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 contain the central nervous system (CNS). The peripheral nervous system (PNS) refers to the peripheral fretfulness (including the cranial nerves) lying outside of the brain and spinal cord.

Pharyngeal slits are openings in the pharynx (the region merely posterior to the rima oris) that extend to the outside surround. In organisms that alive 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 water that enters the oral fissure. The endostyle is a strip of ciliated fungus-producing tissue in the floor of the throat. 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, requite rise to the oral jaw from the offset pharyngeal curvation, with the second arch becoming the hyoid and jaw support.

The post-anal tail is a posterior elongation of the body, extending beyond the anus. The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species, such as fishes. In some terrestrial vertebrates, the tail also helps with balance, courting, and signaling when danger is near. In humans and other keen apes, the mail-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 evolution of chordates and five characteristics that they share.

Chordates and the Evolution of Vertebrates

Two clades of chordates are invertebrates: Cephalochordata and Urochordata. Members of these groups besides possess the five distinctive features of chordates at some point during their development.

Cephalochordata

Members of Cephalochordata possess a notochord, dorsal hollow tubular nerve 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 proper noun. Although the neural tube also extends into the head region, there is no well-defined brain, and the nervous organisation is centered effectually 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 than 500 one thousand thousand years sometime. 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 usually found buried in sand at the bottom of warm temperate and tropical seas. Cephalochordates are suspension feeders. A h2o electric current is created by cilia in the oral cavity, and is filtered through oral tentacles. Water from the mouth then enters the pharyngeal slits, which filter out food particles. The filtered h2o collects in a gill sleeping room chosen the atrium and exits through the atriopore. Trapped nutrient particles are defenseless in a stream of mucus produced by the endostyle in a ventral ciliated fold (or groove) of the throat and carried to the gut. Almost gas exchange occurs across the trunk surface. Sexes are separate and gametes are released into the water 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 five central characteristics of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.

Urochordata

The ane,600 species of Urochordata are also known equally tunicates ((Figure)). The name tunicate derives from the cellulose-similar carbohydrate cloth, called the tunic, which covers the outer torso of tunicates. Although tunicates are classified every bit chordates, the adults do not have a notochord, a dorsal hollow nerve string, or a post-anal tail, although they do take pharyngeal slits and an endostyle. The "tadpole" larval form, however, possesses all five structures. Most tunicates are hermaphrodites; their larvae hatch from eggs within the adult tunicate'south torso. Later hatching, a tunicate larva (possessing all five chordate features) swims for a few days until it finds a suitable surface on which it tin can attach, normally in a dark or shaded location. Information technology then attaches via the head to the surface and undergoes metamorphosis into the adult form, at which indicate the notochord, nervus 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 photo shows a colony of the tunicate Botrylloides violaceus. (b) The larval stage of the tunicate possesses all of the features characteristic of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, an endostyle, and a postal service-anal tail. (c) In the adult stage, the notochord, nerve cord, and tail disappear, leaving but the pharyngeal slits and endostyle. (credit: modification of work by Dann Blackwood, USGS)

Adult tunicates may be either solitary or colonial forms, and some species may reproduce by budding. Most tunicates alive a sessile existence on the ocean flooring and are suspension feeders. All the same, bondage of thaliacean tunicates chosen salps ((Figure)) tin can swim actively while feeding, propelling themselves as they move 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 textile is filtered out of this water past a mucous cyberspace produced by the endostyle and is passed into the intestine via the activeness of cilia. The anus empties into the excurrent siphon, which expels wastes and water. Tunicates are found in shallow ocean waters around the world.

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

Subphylum Vertebrata (Craniata)

A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial basic ((Figure)). Virtually bilaterally symmetrical animals take a caput; of these, those that take a cranium incorporate the clade Craniata/Vertebrata, which includes the primitively jawless Myxini (hagfishes), Petromyzontida (lampreys), and all of the organisms called "vertebrates." (We should note that the Myxini take a cranium but lack a backbone.)

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

Members of the phylum Craniata/Vertebrata display the 5 characteristic features of the chordates; even so, members of this grouping also share derived characteristics that distinguish them from invertebrate chordates. Vertebrates are named for the vertebral column, equanimous of vertebrae—a series of separate, irregularly shaped basic joined together to grade a courage ((Figure)). Initially, the vertebrae course in segments around the embryonic notochord, but eventually replace it in adults. In most derived vertebrates, the notochord becomes the nucleus pulposus of the intervertebral discs that cushion and support side by side vertebrae.

A vertebrate skeleton. Vertebrata are characterized by the presence of a backbone, such equally the one that runs through the center of this fish. All vertebrates are in the Craniata clade and have a cranium. (credit: Ernest V. More than; 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 notwithstanding existence examined, information technology appears that the Craniata/Vertebrata are a monophyletic group that shares the v basic chordate characteristics with the other 2 subphyla, Urochordata and Cephalochordata. Traditional phylogenies place the cephalochordates as a sis clade to the chordates, a view that has been supported past most electric current molecular analyses. This hypothesis is further supported past the discovery of a fossil in Red china from the genus Haikouella. This organism seems to be an intermediate grade between cephalochordates and vertebrates. The Haikouella fossils are about 530 one thousand thousand years onetime and announced similar to modern lancelets. These organisms had a brain and eyes, as do vertebrates, but lack the skull constitute in craniates. ¹ This testify suggests that vertebrates arose during the Cambrian explosion.

Vertebrates are the largest group of chordates, with more than 62,000 living species, which are grouped based on anatomical and physiological traits. More than 1 classification and naming scheme is used for these animals. Here nosotros will consider the traditional groups Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia, which institute classes in the subphylum Vertebrata/Craniata. Virtually all modern cladists classify birds inside Reptilia, which correctly reflects their evolutionary heritage. Thus, we at present have the nonavian reptiles and the avian reptiles in our reptilian nomenclature. Nosotros consider them separately only for convenience. Further, we will consider hagfishes and lampreys together as jawless fishes, the Agnatha, although emerging nomenclature schemes carve up them into chordate jawless fishes (the hagfishes) and vertebrate jawless fishes (the lampreys).

Animals that possess jaws are known equally gnathostomes, which means "jawed oral fissure." Gnathostomes include fishes and tetrapods. Tetrapod literally means "iv-footed," which refers to the phylogenetic history of various land vertebrates, even 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 also refer to the extinct fishlike groups that gave rise to the tetrapods. Tetrapods can be farther divided into two groups: amphibians and amniotes. Amniotes are animals whose eggs incorporate four extraembryonic membranes (yolk sac, amnion, chorion, and allantois) that provide diet and a water-retaining environment for their embryos. Amniotes are adapted for terrestrial living, and include mammals, reptiles, and birds.

Section Summary

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

Visual Connection Questions

(Effigy) Which of the following statements near mutual features of chordates is true?

1. The dorsal hollow nerve string is part of the chordate primal nervous organisation.
2. In vertebrate fishes, the pharyngeal slits become the gills.
3. Humans are not chordates considering humans practice non have a tail.
4. Vertebrates do not have a notochord at whatever betoken in their development; instead, they have a vertebral cavalcade.

(Figure) A

Review Questions

Which of the following is not contained 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 besides 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 feature 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? Exist sure to compare the notochord with the corresponding structure in adults.

The notochord is a flexible construction that provides support for the embryo's body and formation of the neural tube. In the adults, the notochord has been replaced by the bony, rigid vertebral column. This loss of flexibility restricts the movement of adult humans, and would brand it unlikely that the embryo would fit inside the small space it is allotted within the uterus.

Footnotes

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

Glossary

Cephalochordata

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

Chordata

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

Craniata

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

attic

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

dorsal hollow nerve cord

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

lancelet

fellow member of Cephalochordata; named for its blade-like shape

notochord

flexible, rod-shaped support construction that is establish in the embryonic stage of all chordates and in the developed stage of some chordates

pharyngeal slit

opening in the throat

post-anal tail

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

tetrapod

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

tunicate

sessile chordate that is a member of Urochordata

Urochordata

clade equanimous of tunicates

vertebral column

serial of separate bones joined together every bit a courage

Vertebrata

members of the phylum Chordata that possess a courage

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

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