Life Kinds Kinds of Animal

post by: BebenBeny 15 Nov 2011


Labeling an animal species "terrestrial" or "aquatic" is often obscure and becomes a matter of judgment. clarification needed

Arthropods (such as flies) are the most abundant terrestrial animals by species count.

Many animals which are considered terrestrial have a life-cycle that is partly dependent on being in water. Penguins, seals and walruses sleep on land and feed in the ocean, yet they are all considered terrestrial. Many insects and all terrestrial crabs (as well as other clades) have an aquatic life cycle stage: their eggs need to be

Animals do not fall neatly into terrestrial or aquatic classification but lie along a continuum - e.g. penguins spend much of their time under water.

laid in and to hatch in water. After hatching there is an early aquatic form, either a nymph or larva.
There are crab species which are completely aquatic, crab species which are amphibious, and crab species which are terrestrial. Fiddler crabs are called “semi-terrestrial” since they make burrows in the muddy substrate to which they retreat during high tides. When the tide is out, fiddler crabs search the beach for food.
The same is true in the Mollusca: many hundreds of gastropod genera and species live in intermediate situations, such as for example, Truncatella. Some gastropods with gills live on land, and others with a lung live in the water.
As well as the purely terrestrial and the purely aquatic animals there are many borderline species. There are no universally accepted criteria for deciding how to label these species.