Caecilians: Anatomy

Summary: Caecilians are unique vertebrates that have some incredible anatomy. Join Kiersten as she takes on a tour of the caecilian body.

 

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

 

Show Notes:

The Amphibian Class by Rebecca Stefoff

Caecilians: An Overview https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/caecilians

“An insight into the skin glands, dermal scales and secretions of the caecilian amphibian Ichthyophis beddomei.” Damodaran Arun, S. Sandy, Mohammad Abdulkader Akbarsha, Omen V. Omen, and Letha Divya. Saudi J Bill Sci, 2020 Oct:27(10): 2683-2690 doi: 10.1016/j.sjbs.2020.06.009

 

Music written and performed by Katherine Camp

 

Transcript

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

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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 out side 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 third thing I like about this wiggly, squiggly amphibian is their anatomy!

We’re going to start on the outside and work our way in by beginning with the skin. Most amphibian skin is slimy because it’s covered by mucus. Caecilians are no exception. They have two types of glands in their skin and one type produces mucus. The mucus covers the entire body so whenever you try to pick up a caecilian it’s slippery and that’s part of the point! Being slippery makes it much harder for predators to get a hold on you.

Another reason for the mucus is to keep the skin moist which helps with temperature regulation and cutaneous respiration. That means you can breath through your skin. 

The second type of skin gland is called a granular gland also known as a poison gland. It does appear that at least some species of caecilians produce a poison in their adult stage. While studying Siphonops annulus, a species of caecilian from Brazil, researchers noticed a concentration of enlarged mucus-producing glands on their head and their bums.

The glands on their head produce mucus to cover their skin as well as lube up their underground burrows to make it easier to move through the tunnels. The glands on their bums release a poisonous mucus that helps in predator defense. 

An extremely unusual and unique characteristic of caecilian skin is that they have scales. Amphibians don’t have scales, but these amphibians do! To make it even weirder their scales are under the top layer of their skin! We don’t know why they have these scales. It may just be an evolutionary hold over from ancestors. But we do know that not all species have scales, which only makes it a bigger mystery. Why do them have them? And what are they used for?

The skin is also segmented with annuli which are grooves that encircle the body. I haven’t found any information on why they have these annuli or what advantage they give the caecilian, but I’m sure there is a purpose for them. 

While we’re still on the outside let’s talk about limbs or legs. Caecilians have none! They are like snakes in this characteristic. Modern day caecilians have no vestigial components of legs at all, no shoulder bones or pelvic girdle indicating that they might have had legs in their evolutionary past. This is a testament to how old these animals are evolutionarily speaking because the fossils we have found from 190 million years ago have legs. We can make an educated guess that the legs became unnecessary as caecilians adapted to live their entire lives underground or underwater. As they evolved the bones that supported these limbs also disappeared.  

In the last episode we discussed senses, so if you’re listening in order you already know that caecilians do not have image processing eyes. Depending on the species the eyes will be covered in skin, bone, or absent all together. Those that still have an eye can probably determine the difference between light and dark but cannot see images. For a more in depth discussion of this, backtrack to episode two.

Since caecilians do not rely on vision to interact with their surroundings, they have developed tentacles that help them smell and feel their environment. The tentacles are located on the face in-between the eye and nostrils. They are short little protrusions that are chemoreceptors. For more on caecilian tentacles check out episode two of this series.

Okay, we’re going to head inside the body through the nares. As we’ve already discovered caecilians can breathe through their skin, but for most of them that does not provide enough oxygen to survive. Most caecilians have a functioning right lung and a vestigial left lung that doesn’t process much at all. The breathing pattern includes a long exhalation with short inhalations through buccopharangeal pumping. Let me explain that sentence. That means they breathe a long breath out and breathe in short breaths by puffing their cheeks and floor of their mouths in and out. This patten of breathing prevents mixing the clean oxygen that comes in and the carbon dioxide that goes out. This seems to unique to caecilians, at least in the amphibian family. The normal respiratory rate of Typhlonectes natans is 4 to 7 breaths per hour!

Most caecilians have at least one lung but two species of caecilians have no lungs at all. They must do all of their respiration through their skin. How coo is that!?

Let’s move on to the skeleton. The most fascinating part of the caecilians skeletal structure is…well, all of it! Since most caecilians dig into soil, whether on land or underwater, their skulls have fused many of the typical individual bones that are found in amphibian skulls so it can withstand the pressure of pushing through the dirt. The head comes to a point at the nose to make it easier to move through substrate. Small, sharp teeth line the inside of the upper and lower jaw. The mouth is on the underside of the head. Three sets of jaw muscles hold the jaw shut tight so no accidental ingestion of soil happens. This is a fascinating adaption to living underground!

Depending on species, caecilians can have 95 to 285 vertebrae that run down the entire body. Double-headed ribs attach to each vertebrae except the one directly behind the skull and the last few toward the tail. The ribs do not support the body structure like some other cylindrical vertebrates. The muscles of the caecilian actually forms a sheath around the skeleton that is attached to the skin with fibrous connective tissue. This allows the skin and muscles to move together. This cylindrical muscle sheath is what gives their body form.

Caecilians lack functional bone marrow which is where blood cells are produced in other vertebrates, so their blood is created by the liver, kidney, spleen, and thymus.  

The digestive tract consists of teeth, tongue, esophagus, stomach, intestines, and a pancreas. Caecilians are carnivores so their digestive tract is set up to digest meat.

Depending the species, the caecilian’s snake-like body ends in a short tail or none at all. The cloaca is located near the tail on the underside of the body. This is an orifice through which waste is dispelled, eggs are laid, and fertilization occurs. Not all at the same time, though.

 

That pretty much covers anatomy for caecilians. I hope you enjoyed learning about their unique physiology because it is my third favorite thing about them.  

 

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

 

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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.