The tongue, a muscular organ in vertebrates, plays a multifaceted role in an animal’s survival. Its primary functions include manipulating food for chewing and swallowing, tasting, and aiding in grooming. For many terrestrial animals, it is also important for vocalization. The tongue’s structure, often covered with taste buds and kept moist by saliva, is highly adapted to these tasks.
Animals Without a Tongue
While common across the animal kingdom, many species have evolved without a tongue. This absence is often linked to their habitat, feeding mechanisms, or evolutionary history. Most fish, for instance, do not possess a true muscular tongue like land vertebrates. Instead, many fish have a bony basihyal on the floor of their mouth, which lacks taste buds and significant musculature.
Among amphibians, the African clawed frog (family Pipidae) is a notable exception that lacks a tongue, feeding primarily underwater. Many invertebrates also manage without a tongue. Echinoderms such as sea stars, sea urchins, and brittle stars are tongueless. Aquatic invertebrates like clams and corals, which are filter feeders, also lack a tongue. Crustaceans, including crabs, rely on specialized mouthparts for feeding. Even some insects, like adult luna moths, do not have mouths or tongues, as they do not feed in their adult stage.
How They Manage Without a Tongue
Animals without a tongue have developed diverse strategies for feeding and swallowing. Fish, for example, primarily use suction feeding. They rapidly open their mouths and expand their pharyngeal cavity, creating negative pressure that draws water and food in. Once food is in their esophagus, jaw and body movements help transport it to their stomachs.
The African clawed frog, living in an aquatic environment, uses its forelimbs to guide food into its mouth, with water assisting swallowing.
Echinoderms like sea stars employ unique methods; sea stars can evert their stomach to digest prey externally. Sea urchins use a jaw-like apparatus called Aristotle’s lantern to scrape food from surfaces.
Crabs utilize specialized mouthparts, including mandibles and maxillae, along with chemoreceptors, to manipulate and process food particles. These structures enable them to tear, grasp, and move food into their digestive system without a tongue.
Why Some Animals Evolved Without Tongues
The absence of a tongue in certain animal species results from evolutionary adaptations driven by environmental pressures and specialized feeding strategies. For many aquatic animals, a muscular tongue is unnecessary for capturing and processing food due to water’s properties. Water’s buoyancy and resistance allow for efficient suction or filter feeding mechanisms.
Fish evolved in water, developing feeding mechanisms based on drawing water and food into their mouths, making a tongue less critical.
In some cases, alternative anatomical structures or behaviors have rendered a tongue redundant or even disadvantageous. Sea urchins, with their Aristotle’s lantern, effectively scrape algae, eliminating the need for a tongue. Similarly, filter feeders like clams and corals have specialized structures to strain microscopic organisms from water, a process not benefiting from a tongue. Their evolutionary path led to highly specialized tools suited to their ecological niches and diets.