Examples of Invertebrate Chordates

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  • 0:01 What Is an…
  • 2:35 The Tunicates
  • 3:20 The Lancelets
  • 3:55 Ancient Invertebrate Chordates
  • 4:32 Lesson Summary
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Lesson Transcript
Instructor: Taormina Lepore

Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology.

What is an invertebrate chordate? In this lesson, we'll discuss what's so different about this unique group of animals and their specialized traits, and take a look at some examples from different groups of chordates.

What Is an Invertebrate Chordate?

The very phrase sounds intimidating - invertebrate chordate - but these little creatures aren't at all scary. They're actually related to us, and their name can be deconstructed to help us understand just what they are.

An invertebrate is any animal without a backbone made up of vertebrae. There are many examples of invertebrate animals, including insects, snails, clams, squids, octopuses and many more. Invertebrates are an incredibly diverse bunch.

But, certain invertebrate animals are also chordates, and that makes them special. A chordate is any animal that has a series of unique characteristics, and the vast majority of chordate animals actually have a backbone! Humans, in fact, are one example of a chordate.

So, how can there be such a thing as an invertebrate chordate? It all ties back to our development as an embryo in our first stages of growth. All human embryos, and in fact all chordate embryos, have the same chordate characteristics. Those specialized traits include:

  • A notochord
  • A dorsal, hollow nerve cord
  • Pharyngeal gill slits
  • A post-anal tail

The notochord is a cartilage rod that runs along the back, or dorsal, side of every chordate at some stage in its life. In humans we lose this notochord and its remnants are absorbed as a part of the cartilage disks that sit in between the vertebral bones in our back.

A dorsal, hollow nerve cord - not to be confused with the notochord - is a hollow nerve cord that also runs along the back of all developing chordate animals. It's a bundle of nerve fibers that eventually connects the brain with the rest of the body and develops into the spinal cord in humans.

All chordate embryos have gill slits, known as pharyngeal gill slits, at one point in their embryological development. In humans the gill slits seal up, and part of the tissue is incorporated into the structures of the throat and inner ear. The word 'pharyngeal' derives from the location of these gill slits at the sides of the pharynx, which is the throat cavity in humans and other vertebrates.

A post-anal tail is a tail that is present after the anus, and all chordates have a tail at some point in their embryological development - even humans.

Invertebrate chordates share all these traits with their backbone-bearing vertebrate chordate cousins. However, they simply don't develop the full set of vertebrae. In this way, invertebrate chordates are considered some of the most basal, or primitive, chordates.

While there is a fossil record for these ancient relatives of ours, there are, amazingly, also examples of invertebrate chordates still alive today. They can be grouped into two large subsets: the tunicates and the lancelets.

The Tunicates

Tunicates, also known as urochordates, are named for their tunic-like surrounding tissue in their adult stage. As adults, tunicates are sessile - that is, they remain rooted to the ocean floor. But as larvae and juveniles, these strange animals swim freely through the ocean and look a little like frog tadpoles. These larvae have all of the four major chordate characteristics, but no backbone, making them invertebrate chordates.

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