The Mexican axolotl (Ambystoma mexicanum) is a unique salamander that remains fully aquatic and retains its juvenile, or larval, characteristics throughout its life, a phenomenon known as neoteny. This permanent aquatic existence means the axolotl possesses a body plan optimized for water, particularly how it manages to eat. Does the axolotl, like many other amphibians, possess a mobile, muscular tongue? Understanding the axolotl’s feeding mechanics begins with a closer look at its oral structure.
Anatomy of the Mouth Floor
Axolotls do not possess the free, muscular, and highly mobile tongue found in terrestrial amphibians or mammals. The structure present in the floor of the axolotl’s mouth is a broad, flat pad of tissue fused to the bottom of its oral cavity. This immobile pad is derived from the hyobranchial apparatus, the cartilaginous and muscular complex that is the precursor to the tongue in amphibians.
In the neotenic axolotl, this apparatus is highly reduced and fixed, serving no active role in the capture or manipulation of prey. If the axolotl were to undergo metamorphosis, this fixed pad would be absorbed and replaced by a fully functional, projectile tongue, similar to other land-dwelling salamanders. In its permanent aquatic state, this structure necessitates a completely different method of feeding.
The Mechanism of Suction Feeding
Since the axolotl cannot use a sticky, mobile tongue to snatch food, it relies on suction feeding, a specialized technique common among many aquatic vertebrates. The process is rapid and involves the coordinated movement of the jaw and the underlying hyoid skeleton. When the axolotl detects prey, it quickly opens its mouth while simultaneously lowering the floor of its buccal cavity.
This rapid expansion of the mouth volume creates a sudden, strong negative pressure inside the oral cavity. The difference in pressure between the mouth and the surrounding water forces a rush of water and the nearby prey item directly into the axolotl’s mouth. High-speed video analysis shows this action occurs in a fraction of a second. Once the prey is secured, the axolotl expels the excess water through its gill slits, while small, peg-like teeth help position the food before it is swallowed whole.
The Impact of Aquatic Life on Tongue Development
The reliance on suction feeding is a direct consequence of the axolotl’s fully aquatic life and neotenic development. For amphibians that live on land, a sticky, projectile tongue is the most effective tool for capturing terrestrial prey. This requires a developed and flexible hyobranchial skeleton and specialized musculature to launch the tongue rapidly outside the mouth.
This terrestrial feeding mechanism is ineffective underwater because the viscosity and resistance of water prevent the necessary speed and distance for a projectile tongue strike. Therefore, the evolutionary pressure to develop a complex, mobile tongue is removed in permanently aquatic species. Instead, the axolotl’s anatomy favors structures that enable buccal expansion, leading to the retention of a reduced, fixed hyobranchial apparatus optimized for creating the vacuum needed for suction. This results in a feeding apparatus suited for capturing small aquatic organisms without the need for a traditional, free-moving tongue.