Skip to main content

Invertebrates · 1 species guide

Microscopic Invertebrates: Tardigrades & Meiofauna

Microscopic invertebrates are animals too small to see clearly without magnification, including tardigrades (water bears), rotifers and many meiofaunal worms and crustaceans; tardigrades survive extreme drying through cryptobiosis and were revived after exposure to open space in 2007.

Size
Most adults are under 1 mm — tardigrades typically 0.3–0.5 mm; confirmation needs a hand lens or microscope.
Tardigrade body
Plump segmented body with four pairs of legs ending in claws — not six legs like insects.
Habitat
Water films on moss, lichen, soil and leaf litter; marine species in sediments.
Cryptobiosis
Tardigrades curl into a dry tun when desiccated — metabolism near zero until rehydration.

Below the threshold of easy naked-eye identification lies a vast animal community in moss films, soil pores and marine sediments. Tardigrades — water bears — are the best-known example: eight-legged invertebrates typically under half a millimetre that enter cryptobiosis when habitats dry.

These animals are not insects and not a single phylum. Rotifers, nematodes and microscopic crustaceans share habitats and ecological roles as grazers and predators at particle scale. Conservation rarely targets them individually, but pollution, drying climates and habitat simplification can remove the microhabitats they need.

Key facts

  • Tardigrades belong to phylum Tardigrada — not insects or crustaceans.
  • Cryptobiosis lets tardigrades survive vacuum, freezing and radiation in the tun state.
  • The 2007 FOTON-M3 mission revived tardigrades after ten days in open space.
  • Rotifers and nematodes share moss and soil films but use different body plans.
  • Most microscopic invertebrate species lack IUCN assessments.
  • Microhabitat loss from drying or pollution can affect even highly tolerant species.

How to recognise them

The features that separate this group in the field, in the order they are usually most useful.

Size
Most adults are under 1 mm — tardigrades typically 0.3–0.5 mm; confirmation needs a hand lens or microscope.
Tardigrade body
Plump segmented body with four pairs of legs ending in claws — not six legs like insects.
Habitat
Water films on moss, lichen, soil and leaf litter; marine species in sediments.
Cryptobiosis
Tardigrades curl into a dry tun when desiccated — metabolism near zero until rehydration.
The confusion pairs
Tardigrade versus mite: mites are arachnids with eight legs but a different body shape and no cryptobiosis. Tardigrade versus insect larva: insects have six legs only.

1 microscopic invertebrates guide

Search or filter by conservation status. Every guide carries sourced facts, IUCN status and FAQs.

Showing 1-1 of 1 animals

Animal group
Microscopic tardigrade with plump segmented body, four pairs of stubby legs and curved claws on a moss fragment
Not Evaluated at phylum level

Other animals

T

Tardigrade

Phylum Tardigrada — water bears and moss piglets

A half-millimetre animal that shuts down its metabolism, dries out, and survives what would kill almost anything else — including the vacuum of space.

Worldwide · Moss and freshwater films

Open guide

Conservation: what this group faces

Microscopic invertebrates are rarely listed individually, but they depend on moss cushions, soil structure and water films that disappear when habitats dry, compact or pollute — losses that standard landscape protection may not detect.

Fund invertebrate & habitat protection Current appeals

Microscopic invertebrates: frequently asked questions

What is a tardigrade?
A microscopic invertebrate in phylum Tardigrada, typically 0.3–0.5 mm long, living in water films on moss and soil. It survives extreme conditions by entering cryptobiosis.
Are tardigrades insects?
No. They have four pairs of legs and belong to their own phylum. Insects have three body segments and six legs.
Did tardigrades survive in space?
Yes, in cryptobiosis. On the 2007 ESA FOTON-M3 mission, tardigrades on the spacecraft exterior were rehydrated and revived after ten days of vacuum and radiation exposure.
Where do you find tardigrades?
In moss, lichen, soil and leaf litter worldwide — anywhere a thin film of water persists intermittently.
Are tardigrades the smallest animals?
No. Several parasitic wasps and rotifers are smaller. Tardigrades are among the most famous microscopic animals.
Are microscopic invertebrates endangered?
Most species are not individually assessed. Widespread tardigrades are not considered threatened, but microhabitat loss is poorly monitored.

Other types of invertebrates

All invertebrate guides Animals A–Z