Caecilians: Locomotion

Summary: Caecilians are legless amphibians, so how do they get around? Join Kiersten as she talks about caecilian locomotion.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show Notes:

“The kinematics of locomotion in caecilians: effects of substrate and body shape” by Anthony Here et. al, J Exp Cool A Ecol Genet Physiol. 2010. Https//pubmed.ncbi.nlm.nih.gov

 

“A comparative study of locomotion in the caecilian Dermophis mexicanus and Typhlonectes natans (Amphibia: Gymnophiona)” by Adam P. Summers and James C. O’Reilly, Zoological  Journal of the Linnean Society, Vol 121, Issue 1, Sept 1997, pls 65-76. Https://doi.org/10.1111/j.1096-3642.1997.tb000147.x

 

Music written and performed by Katherine Camp

 

Transcript

(Piano music plays)

Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

(Piano music stops)

Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right outside our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

This episode continues caecilians and the fifth thing I like about these supercool amphibians is the way they get around. 

In previous episodes, we have clearly established that caecilians do not have legs, so you may have been asking yourself, how do they get around? Excellent question. Let’s get the answer.

Caecilians are definitely not the only no-legged animal on planet Earth. There are snakes, glass lizards, and fish that do not have legs. Each of these examples have a unique way of locomotion. Caecilian locomotion is something that blows my mind!     

In the last episode we learned that caecilians are divided into ten different families. Most of those families are terrestrial, which means, according to the Oxford Dictionary, of, on, or relating to the earth. Furthermore, many terrestrial caecilians, are fossorial which means they live underground. Nine of our ten families are considered terrestrial caecilians.

So how exactly do caecilians create motion? They use hydrostatic movement. Hydrostatic motion is created when one set of muscles contracts in a circular and longitudinal pattern and another set of muscles stretches in response. Think of how a jellyfish moves. That in and out, almost like breathing, motion is how hydrostatic movement works. Many species of invertebrates use hydrostatic systems to move and several species of vertebrates use hydrostatic systems in specific body parts. 

What makes caecilian hydrostatic locomotion unique is that they are the first known vertebrate to use their entire body as a hydrostatic system for locomotion. How could this get more interesting? I shall tell you! Hydrostatic movement generally depends on utilizing fluid filled portions of the body or vertebrae, but caecilians hydrostatic motion depends on a criss-cross array of tendons that surround their body cavity. Caecilians' skin and skeleton move independently of each other. Muscles do not attach the skin to the skeleton like other vertebrates. This allows them to create twice the maximum forward force of similar sized burrowing snakes that rely on longitudinal movement. 

This is one more example of what makes caecilians so unique in the animal kingdom.

Now that we know exactly how terrestrial caecilians create forward motion let’s look at another characteristic that is influenced by their fossorial lifestyle.

As you know, caecilians don’t have feet, so instead their skull bones have adapted into the perfect shape to move through the soil. They’re skulls are often described as wedge-shaped, compact, and robust. Sounds a lot like a shovel which would be perfect for digging through soil!

Fossorial caecilians’ skull bones have actually fused together in ways that other animals’ skull bones are not fused. There are two types of skull structures in caecilians. The first type is zygokrotaphic in which the skull is perforated between the squamosal, or the side of the skull and the parietal, or the top of the skull. The second type of skull is stegokrotaphic which means the skull in completely roofed. 

These two skull types are incredibly interesting to researchers and have inspired several scientific studies. One study investigated whether the amount of tunneling a species does determines which skull formation is found in their family. The thought was that the completely roofed skull formation would be  better suited to caecilians that burrow in soil more than other species that live mainly in leaf litter. To withstand the force needed to push through the soil a completely fused skull would be better, right? 

What investigators found did not support this hypothesis. There was no evidence showing caecilians with stegokrotaphic skulls had increased burrowing activity. Skull shape may be more influenced by what they eat instead, we’ll talk about this more in next week’s episode.

While investigating this hypothesis the researchers did discover that cranial shape varies greatly throughout caecilians. Even though there is variability in the position of the mouth, the temporal perforation of the skull, and the closure of the eye orbits, caecilian skulls are are generally bullet shaped which helps make burrowing much easier. 

Scientists are always asking questions and a group of researchers studying caecilian movement wanted to know if the length of a caecilian impacted the way they moved. Using x-ray video these scientists recorded the movement of five different species of caecilian that ranged in size. What they discovered was that as the length of the caecilian increased their ability to create the internal concertina motion of hydrostatic movement decreased. As the caecilians increased in length they lost the skin and skeletal independent movement because of the increase in body length. The larger species depended more on lateral movement, even though they are still capable of concertina movement. 

On an interesting note, in all species locomotion choice was dependent on substrate. When they were burrowing through soil they used a whole body or concertina motion to move forward; yet, when they were above the soil they used a lateral movement. This movement is similar to how snakes move in that side to side slithering motion.

Family Typhlonectidae contains our aquatic caecilians. There are 13 species in this family and they all live their entire lives under the water. They also burrow into soil but since the substrate is underwater it’s often more sandy or silty. Many species in this family have lost the concertina movement of terrestrial caecilians. Instead, they rely on a lateral motion to move through the water and soft substrate.

That’s it for caecilian locomotion, I hope you enjoyed this episode because it’s my fifth favorite thing about this awesome animal.

If you're enjoying this podcast please recommend me to friends and family and take a moment to give me a rating on whatever platform your listening. It will help me reach more listeners and give the animals I talk about an even better chance at change. 

 

Join me next week for another thing I like about caecilians!

 

(Piano Music plays) 

This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.