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Invertebrate Chordates Study Guide

Invertebrate chordates belong to the phylum Chordata group. They are mainly classified into three major subphyla: Vertebrata, Urochordata, and Cephalochordata.

Introduction:

A chordate is an animal of phylum Chordata. All Chordata possess five main characteristics. During their maturity stage, the chordates get different features from their families. The five synapomorphies includes notochord, pharyngeal slits, nerve cord, thyroid, and a post-anal tail. Chordates get this name from their characteristics known as “notochord,” which plays a vital role in the chordate structure and movement.

Chordates include both vertebrates and invertebrates that have a notochord. Invertebrate chordates do not have a backbone. Invertebrate chordates include tunicates and lancelets. Both are primarily marine organisms.

Invertebrate chordates:

Invertebrate chordates are the animals of phylum Chordata that have notochord at the point of their growth, but invertebrate chordates don’t have a backbone. A notochord is a rod-like structure that helps as a very important function and is attached to their muscles.

In humans who are vertebrate chordates, the notochord is replaced with a spinal cord. This difference is the main feature that separates invertebrate chordates from vertebrates chordates. The Chordata is divided into three divisions:

  • Vertebrata (Fish, amphibians, birds, reptiles & animals)
  • Tunicata (Salps, Sea squirts)
  • Cephalochordata (lancelets)

All invertebrate chordates belong to Tunicata and Cephalo.

Invertebrate chordate Source

Characteristics of chordates

  1. All chordates have a dorsal nerve tube. This tube or nerve cord is dorsal to the notochord. In invertebrate chordates, it is generally seen in the larval stage of development but not the adult stage. In vertebrates, the neural tube develops into the brain and spinal cord, which comprise the central nervous system.

  2. Chordates have a notochord that expands from the animal's head to its tail, towards its back, and dorsal to its digestive region. It has a semi-flexible structure to muscles which help the animal to move. The notochord is developed between the digestive tube and the nerve cord; it provides rigid skeletal support and a flexible location.

  3. Invertebrate chordates have pharyngeal gill slits. These structures are important for both feeding and respiration both. In vertebrates, this is modified into gill supports & in jawed fishes to support their jaws.

  4. Chordates have a post-anal tail till their body extension goes far towards the end of their digestive region, and it is seen only in the early stages of development in a few of the chordates. In some vertebrates, the tails also help balance and signal when they are in danger.

  5. All invertebrate chordates have an endostyle. This feature is found in the endpoint of the pharynx & produces mucus to help in filtering food from the environment.

Tunicate

A tunicate is a marine invertebrate animal; they are a member of Tunicata subphylum. It is a part of the Chordata, which includes animals with dorsal nerves, cords, and notochords. The subphylum was also called Urochordata, and sometimes this term is still used for this type of animal. Adult tunicates are barrel-shaped and have two opening points.

Urochordata examples include:

  • Sea peach
  • Sea pork
  • Golden star Tunicate

Cephalochordate

A cephalochordate is an animal in the chordate subphylum. They are commonly known as lancelets. Cephalochordate is commonly found in warm temperate and tropical seas. With the presence of the notochord, they can swim and manage the tides of coastal environments. They are only a few centimeters in length.

Cephalochordata examples include:

  • Lampreys
  • Sea squirts

Lancelets

Lancelets like in the ocean and are eel-like organisms. They have a nerve cord, but do not have a brain or vertebrae.

Difference between vertebrates and invertebrates

Invertebrates vs vertebrates Source

  1. Vertebrates are animals that have a backbone inside their body. Invertebrate animals don’t have a backbone inside their body.
  2. Examples for vertebrates are fish, amphibians, reptiles, birds, and mammals. Examples of invertebrates are worms, jellyfish.
  3. Vertebrates contain skeletons inside their body, but invertebrates don’t possess skeletons.
  4. All invertebrates possess an open circulatory system while all vertebrates have a closed circulatory system.
  5. Many invertebrates have compound eyes; vertebrates don't have compound eyes.
  6. 95% of animal species are invertebrates, while the remaining 5% are vertebrates.
  7. Invertebrates have a simple nervous system; vertebrates have a complex nervous system.

All vertebrates are chordates, but all chordates are not vertebrates:

  • All chordates have a notochord.
  • Chordates include urochordates, cephalochordates, and vertebrates.
  • Invertebrate notochord is replaced by the vertebral column, i.e., backbone; however, the vertebral column is not present in a protochordate.
  • Thus, all vertebrates are chordates, but all chordates are not vertebrates.

Conclusion:

  • Chordates include both vertebrates and invertebrates that have a notochord.
  • Invertebrate chordates do not have a backbone. Invertebrate chordates include tunicates and lancelets. Both are primarily marine organisms.
  • A notochord is a rod-like structure that is primarily made up of a core of glycoproteins.
  • The notochord is replaced with a spinal cord in the case of humans who are vertebrate chordates.
  • This difference is the main feature that separates invertebrate chordates from vertebrate chordates or animals with a backbone.
  • A tunicate is a marine invertebrate animal. They are members of the tunicata subphylum. A cephalochordate is an animal in the chordate subphylum. They are commonly known as lancelets.

FAQs:

1. What are invertebrate chordates?

Chordates include vertebrates and invertebrates that have a notochord. Invertebrate chordates are the ones that do not have a backbone.

2. What are examples of invertebrate chordates?

Examples of Invertebrate chordates are tunicates and lancelets.

3. What are the two main groups of invertebrate chordates?

The two main groups of invertebrate chordates are Urochordata and Cephalochordata.

4. What are the seven characteristics of a chordate?

The 7 main characteristics are:

  • Notochord
  • Dorsal Nerve Cord
  • Pharyngeal Slits
  • Post anal Tail
  • Urochordata
  • Cephalochordata
  • Lampreys

5. What characteristics distinguish invertebrates and chordates?

Invertebrate chordates are the animals of the phylum Chordata that possess notochord at some point in their development but no backbone. This is the main characteristic that separates invertebrate chordates from vertebrate chordates or animals with a backbone.

6. What are the major groups of vertebrate chordates?

Chordates are divided into three subphyla:

  • Vertebrata (Fish, amphibians, reptiles, birds, and mammals)
  • Tunicata (Sea squirts and salps)
  • Cephalochordata (Lancelets)

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Sources:

  1. Invertebrate Chordates. https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/11.13/primary/lesson/invertebrate-chordates-bio/. Accessed 9 Dec. 2021.
  2. Biology of Invertebrate Chordates. https://www.thoughtco.com/biology-of-invertebrate-chordates-4156566. Accessed 9 Dec. 2021.
  3. Examples of Invertebrate Chordates. https://study.com/academy/lesson/examples-of-invertebrate-chordates.html. Accessed 9 Dec. 2021.