Tardigrades, commonly known as water bears or moss piglets, are microscopic invertebrates known for their remarkable resilience. These tiny creatures, typically 0.5 mm in length, are characterized by their plump, segmented bodies and eight short legs, each ending in claws or sticky pads. They inhabit an astonishing range of environments globally, from mountain peaks and ocean depths to tropical rainforests and polar regions. Tardigrades are frequently found in moist habitats, such as damp moss, lichen, leaf litter, freshwater, and marine sediments.
Primary Food Sources
Most tardigrade species primarily consume the fluids of plant cells. This herbivorous diet is common among terrestrial tardigrades, which often reside in mosses, lichens, and algae. They use specialized mouthparts to pierce plant cell walls and then draw out the nutrient-rich contents. Algae, in particular, serve as a significant and consistent food source, especially for aquatic tardigrade species, providing them with essential nutrients.
Different species exhibit preferences for specific plant matter. Some favor flowering plant cells, while others primarily feed on moss or various algae forms. This plant-based diet forms the foundation for most tardigrade populations, reflecting their widespread presence in vegetated environments. Their ability to extract fluids from microscopic plant cells highlights a fundamental feeding strategy.
Diverse Feeding Strategies
Beyond their primary herbivorous habits, tardigrades display diversity in their feeding strategies. Some species are predatory, hunting and consuming other microscopic invertebrates. This can include smaller organisms like rotifers and nematodes, which are commonly found in the same microhabitats as tardigrades.
Certain predatory tardigrade species have even been observed engaging in cannibalism, feeding on other, smaller tardigrades. Additionally, some tardigrades are known to feed on bacteria and detritus, which is dead organic matter. This makes them important contributors to nutrient cycling by breaking down organic material in their environments.
The Eating Mechanism
Tardigrades possess a distinct feeding apparatus. Their mouth is equipped with two sharp, retractable structures known as stylets. These stylets function like tiny spears, enabling the tardigrade to pierce the outer layers of their food source, whether a plant cell wall or the cuticle of a small invertebrate.
Once the stylets create an opening, the tardigrade utilizes a muscular, sucking pharynx located in its head. This pharynx acts as a pump, generating suction to draw internal fluids or cellular contents from the pierced prey into the digestive system. This process effectively allows them to “drink” the insides of their food. A pair of salivary glands also secrete digestive fluid into the mouth and produce replacement stylets when the animal molts.