In adults the notochord runs the full length of the body almost to the tip of the front end Fig. For this reason scientists assign lancelets to another subphylum called Cephalochordata from the Greek root words cephalo - meaning head and chord meaning string.
Muscles are arranged in V-shaped segments, much as they are in fish, along the entire body on either side of the notochord. When the muscles contract, they pull the notochord from side to side, producing a wiggly swimming motion. The food-filtering apparatus of lancelets works much as it does in tunicates, but it is arranged differently Fig.
The mouth has two sets of tentacles that trap and capture large food particles. The mouth opens into a large pharynx that has slits along both sides. A ventral endostyle secretes mucous material that coats the inside of the pharynx.
Water containing suspended food particles moves through the mouth opening into the pharynx and filters through the slits. The filtered water passes into the atrium surrounding the pharynx and out the atrial siphon on the ventral side of the body. Food and mucous material move into the digestive tract, where the small filtered particles are digested and absorbed. The indigestible remains pass out of the body through the anus behind the atrial opening on the ventral side.
This vessel has muscular walls that pulsate to move the blood. The blood flows through a series of vessels in the pharyngeal arches up to a dorsal blood vessel and then to the other organs of the body. Following the chordate body plan, the dorsal hollow nerve cord runs the length of the body above the notochord. But there is no anterior enlargement of the nerve tube that could be called a brain.
The nerve tube divides into segmental branches that control the contraction of the segmental muscles. This document may be freely reproduced and distributed for non-profit educational purposes.
Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Home Biological Invertebrates Phylum Chordata. Phylum Chordata. MS-LS Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.
MS-LS Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms.
MS-LS Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories. MS-LS Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation. HS-LS Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
HS-LS Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence.
The content and activities in this topic will work towards building an understanding of the phylum Chordata. Introduction to Phylum Chordata The phylum Chordata consists of animals with a flexible rod supporting their dorsal or back sides. All chordates share the following common features that are unique to the group: The notochord is a stiff but flexible rod of cells and connective tissue from the Greek root words noto meaning back and chord meaning string that gives the phylum its name, Chordata.
In some chordates the notochord is a major support structure Fig. In fishes, amphibians, reptiles, birds, and mammals, the notochord is present only in the embryo. Because bony, segmented vertebrae replace it during later stages of development, these animals are assigned to the subphylum Vertebrata.
Tunicates and lancelets are examples of invertebrate chordates since they have a notochord, but it does not develop into a vertebral column. Pharyngeal slits are in the pharynx , the region of the digestive tract just behind the mouth Fig. In some chordates, such as tunicates, these slits filter food from the water. In other chordates, such as fish, they are respiratory structures. In humans they appear only in the early embryo as a few indentations, not as open slits.
They are therefore called pharyngeal clefts in a human embryo. The dorsal hollow nerve tube lies above the notochord Fig. As the nerve tube grows, its walls thicken, almost eliminating the central hollow space. A dorsal hollow nerve tube is a common feature of all chordates, including humans, in both embryonic and mature stages. When a whale dies and its carcass sinks to the bottom, it becomes a source of food where it is generally scarce.
Pelagic tunicates are gelatinous chordates that live in the midwater zone of the ocean. There are few different kinds including salps, doliolids and pyrosomes. Reading: More about pelagic tunicates. Larvaceans are tunicates that live in the deep sea water column.
These small animals build mucus nets that they live inside and that trap tiny bits of detritus and animal parts—called marine snow—drifting down to the bottom of the ocean. Scientists from the Monterey Bay Aquarium Research Institute estimated the amount of food and its carbon content brought to the sea floor by the abandoned larvacean houses.
Salps, a gelatinous tunicate, play a major role in the ecosystem of the deep sea. One of the reasons is the sheer number of them. Scientists have hypothesized that a doubling or quadrupling of genes occurred in vertebrate evolution. Decoding the genome of the ancient marine chordate the lancelet or Amphioxus, showed that vertebrate evolution was indeed characterized by the quadrupling of the genes of primitive ancestors.
Reading: Scientists have decoded the genes of an ancient fish, the coelacanth. The coelacanth genome is likely to shed light on the central evolutionary question of what genetic alterations were needed to change a lobe-finned fish into the first land-dwelling tetrapod. Lobe-finned fish, like the coelacanth and lungfish are known to zoologists as sarcopterygians, which means fleshy fins.
Tetrapods, including humans, are descended from this group, and the coelacanth is more closely related to people than to other fish. Scientists have decoded the genes of an ancient fish, the coelacanth. Jaws, the Early Years. A newly discovered fish fossil is challenging what we know about the evolution of jaws.
The million-year-old fossil, found by scientists in Yunnan, China, appears to have the kind of bony jaw associated with modern fish. This suggests that jaws as we now know them may have evolved much earlier than previously thought.
Skip to main content. Images Download cows. Download cows. Download elephants. Download giraffe. Download tunicate. Download clownfish. Download yellowfish. Download bonobo. Download cobra-snake. Download fish-jaw1. Download fish-jaw2. 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 most conspicuous and familiar members of Chordata are vertebrates, but this phylum also includes two groups of invertebrate chordates. Animals in the phylum Chordata share four key features that appear at some stage during their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail Figure 2.
In some groups, some of these are present only during embryonic development. The chordates are named for the notochord , which is a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and in the adult stage of some chordate species.
It is located between the digestive tube and the nerve cord, and provides 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 and serves as a support for the developing embryonic body. The notochord, however, is not found in the postnatal stage of vertebrates; at this point, it has been replaced by the vertebral column that is, the spine.
Figure 2. In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Which of the following statements about common features of chordates is true? The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development. In chordates, it is located dorsal to the notochord.
In contrast, 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 compose 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.
Some invertebrate chordates use the pharyngeal slits to filter food out of the water that enters the mouth. In vertebrate fishes, the pharyngeal slits are modified into gill supports, and in jawed fishes, into jaw supports. In tetrapods, the slits are modified into components of the ear and tonsils. Tetrapods include amphibians, reptiles, birds, and mammals. 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, the post-anal tail is vestigial, that is, reduced in size and nonfunctional. Watch this video discussing the evolution of chordates and five characteristics that they share.
Chordata also contains two clades of invertebrates: Urochordata and Cephalochordata. Members of these groups also possess the four distinctive features of chordates at some point during their development. Members of Urochordata are also known as tunicates Figure 3. The name tunicate derives from the cellulose-like carbohydrate material, called the tunic, which covers the outer body of tunicates. Although adult tunicates are classified as chordates, they do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits.
The larval form, however, possesses all four structures.
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