Tardigrades, often called “water bears” or “moss piglets,” are microscopic invertebrates known for their extraordinary resilience. These tiny creatures can survive conditions lethal to most other life, including extreme temperatures, pressures, radiation, and even the vacuum of space. This article explores the distinctive appearance of tardigrades, offering insights into what these fascinating micro-animals look like.
General Appearance and Size
Tardigrades have a distinctive, plump body shape, contributing to their common names. They are barrel-shaped or cylindrical, resembling miniature bears with eight legs. Their bodies are segmented, featuring a head region and four main body segments.
These micro-animals range in length from 0.05 to 1.2 millimeters, with some species reaching 1.3 millimeters. This minute size makes them invisible to the unaided human eye. A microscope is necessary to observe their details.
Distinctive Features
Tardigrades have eight stubby legs, arranged in four pairs, with each leg unjointed and hollow. The first three pairs are directed downwards for locomotion, while the hindmost pair points backward, aiding in grasping. Each leg ends in four to eight claws, which allow them to grip surfaces. Some species have claws modified into sticky pads.
Their head region is indistinct from the rest of the body, housing a specialized oral apparatus. This structure, known as the buccal apparatus, includes a mouth, a muscular sucking pharynx, and two sharp, needle-like stylets. These stylets pierce the cell walls of their food, such as plant cells, algae, or small invertebrates, allowing the tardigrade to suck out internal fluids. Tardigrades have a tough, flexible outer covering called a cuticle, which acts as an exoskeleton. This cuticle is periodically shed as the tardigrade grows, a process known as molting.
Coloration and Transparency
Many tardigrades are semi-transparent or translucent, allowing visibility of their internal organs under a microscope. This transparency can vary, with some species appearing almost entirely clear. Their coloration varies widely, influenced by several factors.
A tardigrade’s color depends on its diet; for example, those consuming algae appear green, while those feeding on detritus take on a brownish hue. Pigments within their cuticle, dissolved materials in their body fluids, or digestive tract contents also contribute to their overall color. Some species display shades of white, pink, orange, yellow, or even reddish tones. This adaptability helps them blend into their diverse microhabitats.
Observing Tardigrades
To observe tardigrades in detail, a microscope is an essential tool. Their microscopic size necessitates magnification to see their barrel-shaped bodies, eight legs, and oral structures. A stereo microscope with a magnification as low as 20x can allow recognition, but higher magnifications, such as 100x to 400x, reveal more intricate features.
Tardigrades are found in various moist environments across the globe, from mountaintops to the deep sea. Common places to locate them include damp moss, lichen, leaf litter, and aquatic sediments. Collecting a sample of moss or lichen and soaking it in water often yields tardigrades for microscopic observation, allowing one to witness their unique movements and physical traits.