What do chordata look like

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 water current is created by cilia in the mouth, and is filtered through oral tentacles. Water from the mouth then enters the pharyngeal slits, which filter out food particles. The filtered water collects in a gill chamber called the atrium and exits through the atriopore.

Trapped food particles are caught in a stream of mucus produced by the endostyle in a ventral ciliated fold or groove of the pharynx and carried to the gut. Most gas exchange occurs across the body surface. Sexes are separate and gametes are released into the water through the atriopore for external fertilization. The 1, species of Urochordata are also known as tunicates Figure. The name tunicate derives from the cellulose-like carbohydrate material, called the tunic , which covers the outer body of tunicates.

Although tunicates are classified as chordates, the adults do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits and an endostyle. 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 then attaches via the head to the surface and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear, leaving the pharyngeal gill slits and the endostyle as the two remaining features of its chordate morphology.

Adult tunicates may be either solitary or colonial forms, and some species may reproduce by budding. Most tunicates live a sessile existence on the ocean floor and are suspension feeders. However, chains of thaliacean tunicates called salps Figure can swim actively while feeding, propelling themselves as they move water through the pharyngeal slits. The primary foods of tunicates are plankton and detritus. Suspended material is filtered out of this water by a mucous net produced by the endostyle and is passed into the intestine via the action of cilia.

The anus empties into the excurrent siphon, which expels wastes and water. Tunicates are found in shallow ocean waters around the world. A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones Figure. Vertebrates are named for the vertebral column, composed of vertebrae —a series of separate, irregularly shaped bones joined together to form a backbone Figure.

Initially, the vertebrae form 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 adjacent vertebrae. Traditional phylogenies place the cephalochordates as a sister clade to the chordates, a view that has been supported by most 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 between cephalochordates and vertebrates. The Haikouella fossils are about million years old and appear similar to modern lancelets. These organisms had a brain and eyes, as do vertebrates, but lack the skull found in craniates.

Vertebrates are the largest group of chordates, with more than 62, living species, which are grouped based on anatomical and physiological traits. More than one classification and naming scheme is used for these animals. Virtually all modern cladists classify birds within Reptilia, which correctly reflects their evolutionary heritage.

Thus, we now have the nonavian reptiles and the avian reptiles in our reptilian classification. We consider them separately only 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.

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 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 nutrition and a water-retaining environment for their embryos. Amniotes are adapted for terrestrial living, and include mammals, reptiles, and birds. Although tunicates are classified as chordates, only the larval form possesses all four common structures.

Adults only maintain pharyngeal slits and lack a notochord, a dorsal hollow nerve cord, and a post-anal tail. Urochordates : a This photograph shows a colony of the tunicate Botrylloides violaceus. Most tunicates are hermaphrodites. After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location.

It then attaches via the head to the surface and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear. Most tunicates live a sessile existence on the ocean floor and are suspension feeders. The primary foods of tunicates are plankton and detritus. Suspended material is filtered out of this water by a mucous net pharyngeal slits and is passed into the intestine via the action of cilia.

The anus empties into the excurrent siphon, which expels wastes and water. Tunicates are found in shallow ocean waters around the world. Members of Cephalochordata possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage. Extinct members of this subphylum include Pikaia , which is the oldest known cephalochordate.

Pikaia fossils were recovered from the Burgess shales of Canada and dated to the middle of the Cambrian age, making them more than million years old.

Extant members of Cephalochordata are the lancelets, named for their blade-like shape. Lancelets are only a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. Like tunicates, they are suspension feeders. With notochord and paired muscle blocks, the lancelet and Pikaia may belong to the chordate group of animals from which the vertebrates have descended.

Cephalochrodates : The lancelet, like all cephalochordates, has a head. Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

Water from the mouth enters the pharyngeal slits, which filter out food particles. The filtered water then collects in the atrium and exits through the atriopore. Both genomic and fossil evidence suggests that vertebrates evolved from craniates, which evolved from invertebrate chordates. The clade Craniata is a subdivision of Chordata.

Members of Craniata posses a cranium, which is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones. The clade Craniata includes all vertebrates and the hagfishes Myxini , which have a cranium but lack a backbone. Hagfish are the only known living animals that have a skull, but not a vertebral column. Hagfish : Although it lacks a backbone, the hagfish is a member of the Craniata clade because it possesses a bony skull.

Clade Craniata : Craniata, including this fish Dunkleosteus , are characterized by the presence of a cranium, mandible, and other facial bones.

Vertebrates are members of the subphylum Vertebrata, the clade Craniata, and the phylum Chordata. Vertebrates display the four characteristic features of chordates, but they are named for the vertebral column composed of a series of bony vertebrae joined together as a backbone.

In adult vertebrates, the vertebral column replaces the embryonic notochord. Vertebrates : Vertebrata are characterized by the presence of a backbone, such as the one that runs through the middle of this fish.

All vertebrates are in the Craniata clade and have a cranium. In the phylum Chordata, the closest relatives of the vertebrates are the invertebrate chordates. Based on the molecular analysis of vertebrate and invertebrate genomes genomics , scientists can determine the evolutionary history of different phylogenetic groups.

According to these genomic analyses, vertebrates appear to be more closely related to the lancelets cephalochordates than to the tunicates urochordates. This suggests that the cephalochordates first diverged from urochordates, and that vertebrates subsequently diverged from the cephalochordates.

This hypothesis is further supported by the fossil of a million-year-old organism with a brain and eyes like a vertebrate, but without the skull found in a craniate. A comparison of the genomes of a lancelet, tunicate, lamprey, fish, chicken, and human confirmed that two whole-genome duplications occurred in the early history of the Vertebrata subphylum. Both fossil and genomic evidence suggests that vertebrates arose during the Cambrian explosion.

The Cambrian explosion was the relatively brief span of time during the Cambrian period during which many animal groups appeared and rapidly diversified. Most modern animal phyla originated during the Cambrian explosion. Vertebrates are members of the subphylum Vertebrata, under the phylum Chordata and under the kingdom Animalia. The chordates are named for the notochord: a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and also in the adult stage of some chordate species.

It is located between the digestive tube and the nerve cord, providing skeletal support through the length of the body. In vertebrates, the notochord is present during embryonic development, at which time it induces the development of the neural tube which serves as a support for the developing embryonic body. The notochord, however, is replaced by the vertebral column spine in most adult vertebrates.

The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development. In chordates, it is located dorsally at the top of the animal to the notochord. In contrast to the chordates, other animal phyla are characterized by solid nerve cords that are located either ventrally or laterally.

The nerve cord found in most chordate embryos develops into the brain and spinal cord, which comprise the central nervous system.

Pharyngeal slits are openings in the pharynx 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.