Terrestrial animal

Thecane toadis a terrestrial animal.

Terrestrial animalsareanimalsthat live predominantly or entirely onland(e.g.cats,chickens,ants,spiders), as compared withaquatic animals,which live predominantly or entirely in the water (e.g.fish,lobsters,octopuses), andsemiaquaticanimals, which rely on both aquatic and terrestrialhabitats(e.g. mostamphibians). Some groups ofinsectsareterrestrial,such asants,butterflies,earwigs,cockroaches,grasshoppersand many others, while other groups are partially aquatic, such asmosquitoesanddragonflies,which pass theirlarvalstages in water.

Alternatively, terrestrial is used to describe animals that live on the ground, as opposed toarborealanimals that live in trees.

Terrestrial classes

The term "terrestrial" is typically applied to species that live primarily on the ground, in contrast toarborealspecies, which live primarily in trees.

There are other less common terms that apply to specific groups of terrestrial animals:

• Saxicolouscreatures are rock dwelling. "Saxicolous" is derived from the Latin wordsaxum,meaning a rock.
• Arenicolouscreatures live in the sand.
• Troglofaunapredominantly live in caves.

Taxonomy

Terrestrial invasion is one of the most important events in thehistory of life.Terrestrial lineages evolved in several animalphyla,among which arthropods, vertebrates and mollusks are representatives of more successful groups of terrestrial animals.

Terrestrial animals do not form a unifiedclade;rather, they share only the fact that they live on land. The transition from an aquatic to terrestrial life by various groups of animals has occurred independently and successfully many times.Most terrestrial lineages originated under a mild ortropical climateduring thePaleozoicandMesozoic,whereas few animals became fully terrestrial during theCenozoic.

If internalparasitesare excluded, free living species in terrestrial environments are represented by the following eleven phyla:

• Gastrotrichs(hairy-backs) live in transient terrestrial water and go dormant during desiccation
• Rotifers(wheel animals) live in transient terrestrial water and go dormant during desiccation
• Nematodes(roundworms) by going dormant during desiccation
• Eutardigrades(water bears) live in transient terrestrial water and go dormant during desiccation
• Flatworms(land planarians) require moist habitats and have restricted range
• Nemerteans(ribbon worms inMonostilifera) require moist habitats and have restricted range
• Onychophora(velvet worms) require moist habitats and have restricted range, the only solely terrestrial phylum
• Annelids(clitellates) require moist habitats, highly diverse and derived from theirmarine relatives
• Arthropods(fully terrestrial members:hexapods,arachnids,myriapods,woodlice,sandhoppers,andterrestrial crabs;semi-terrestrial members includewater fleas,copepods,andseed shrimp)
• Mollusks(gastropods:land snailsandslugs)
• Chordates(tetrapods;semiterrestrial members:amphibious fish)

Roundworms, gastrotrichs, tardigrades, rotifers and some smaller species of arthropods and annelids are microscopic animals that require a film of water to live in, and are therefore considered semi-terrestrial.Flatworms, ribbon worms, velvet worms and annelids all depend on more or less moist habitats. The three remaining phyla, arthropods, mollusks, and chordates, all contain species that haveadaptedtotally to dry terrestrial environments, and which have no aquatic phase in their life cycles.

Difficulties

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.

Labeling an animal species "terrestrial" or "aquatic" is often obscure and becomes a matter of judgment. Many animals considered terrestrial have a life-cycle that is partly dependent on being in water.Penguins,seals,andwalrusessleep on land and feed in the ocean, yet they are all considered terrestrial. Many insects, e.g.mosquitos,and allterrestrial crabs,as well as other clades, have an aquatic life cycle stage: their eggs need to be laid in and to hatch in water; after hatching, there is an early aquatic form, either anymphorlarva.

There are crab species that are completely aquatic, crab species that are amphibious, and crab species that are terrestrial.Fiddler crabsare 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 themollusca.Many hundreds ofgastropodgenera 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, thus some assignments are disputed.

Terrestrial panarthropods

Fossil evidence has shown that sea creatures, likely arthropods, first began to make forays onto land around 530 million years ago, in the EarlyCambrian.There is little reason to believe, however, that animals first began living reliablyon land around that time. A more likely hypothesis is that these early arthropods' motivation for venturing onto dry land was to mate (as modern horseshoe crabs do) or to lay eggs out of the reach of predators. Three groups of arthropods had independently adapted to land by the end of the Cambrian:myriapods,hexapodsandarachnids.By the lateOrdovician,they may have fully terrestrialized. There are other groups of arthropods, all frommalacostracancrustaceans, which independently became terrestrial at a later date:woodlice,sandhoppers,andterrestrial crabs.Additionally, the sisterpanarthropodangroupsOnychophora(velvet worms) are also terrestrial, while theEutardigradaare also adapted for land to some degree; both groups probably becoming so during theEarly Devonian. Among arthropods, many microscopic crustacean groups likecopepodsandamphipodsandseed shrimpcan go dormant when dry and live in transient bodies of water.

Vertebrate terrestrialization

Main article:Vertebrate land invasion

By approximately 375 million years agothe bony fish best adapted to life in shallow coastal/swampy waters (such asTiktaalik roseae). Thanks to relatively strong, muscular limbs (which were likely weight-bearing, thus making them a preferable alternative to traditional fins in extremely shallow water),and lungs which existed in conjunction with gills,Tiktaalikand animals like it were able to establish a strong foothold on land by the end of the Devonian period. In theCarboniferous,tetrapods (losing their gills) became fully terrestrialized, allowing their expansion into most terrestrial niches, though later on some will return to being aquatic and conquer the air also.

Terrestrial gastropods

Main articles:land snail,semi-slug,andslug

Gastropodmollusks are one of the most successful animals that have diversified in the fully terrestrial habitat.They have evolved terrestrial taxa in more than nine lineages.They are commonly referred to asland snailsandslugs.

Terrestrial invasion of gastropod mollusks has occurred inNeritopsina,Cyclophoroidea,Littorinoidea,Rissooidea,Ellobioidea,Onchidioidea,Veronicelloidea,Succineoidea,andStylommatophora,and in particular, each of Neritopsina, Rissooidea and Ellobioidea has likely achieved land invasion more than once.

Most terrestrialization events have occurred during thePaleozoicorMesozoic.Gastropods are especially unique due to several fully terrestrial and epifaunal lineages that evolved during theCenozoic.Some members of rissooidean familiesTruncatellidae,Assimineidae,andPomatiopsidaeare considered to have colonized to land during the Cenozoic.Most truncatellid and assimineid snails amphibiously live inintertidalandsupratidalzones frombrackish waterto pelagic areas.Terrestrial lineages likely evolved from such ancestors.Therissooideangastropod familyPomatiopsidaeis one of the few groups that have evolved fully terrestrial taxa during the late Cenozoic in theJapanese Archipelagoonly.Shifts from aquatic to terrestrial life occurred at least twice within two Japanese endemic lineages in Japanese Pomatiopsidae and it started in theLate Miocene.

About one-third of gastropod species are terrestrial.In terrestrial habitats they are subjected to daily and seasonal variation in temperature and water availability.Their success in colonizing different habitats is due to physiological, behavioral, and morphological adaptations to water availability, as well as ionic and thermal balance.They are adapted to most of the habitats on Earth.The shell of a snail is constructed ofcalcium carbonate,but even in acidic soils one can find various species of shell-less slugs.Land-snails, such asXerocrassa seetzeniandSphincterochila boissieri,also live in deserts, where they must contend with heat and aridity.Terrestrial gastropods are primarily herbivores and only a few groups are carnivorous.Carnivorous gastropods usually feed on other gastropod species or on weak individuals of the same species; some feed on insect larvae or earthworms.

Semi-terrestrial animals

Semi-terrestrial animals are macroscopic animals that rely on very moist environments to thrive, they may be considered a transitional point between true terrestrial animals and aquatic animals. Among vertebrates, amphibians have this characteristic relying on a moist environment and breathing through their moist skin while reproducing in water.

Many other animal groups solely have terrestrial animals that live like this:land planarians,land ribbon worms,roundworms(nematodes), andland annelids(clitellates) who are very primitive andbreathe through skin.

Clitellatesor terrestrial annelids demonstrate many unique terrestrial adaptations especially in their methods of reproduction, they tend towards being simpler than their marine relatives, thebristleworms,lacking many of the complex appendages the latter have.

Velvet worms are prone to desiccation not due to breathing through their skin but due to their spiracles being inefficient at protecting from desiccation, like clitellates they demonstrate extensive terrestrial adaptations and differences from their marine relatives including live birth.

Geoplankton

Many animals live in terrestrial environments by thriving in transient often microscopic bodies of water and moisture, these includerotifersandgastrotrichswhich lay resilient eggs capable of surviving years in dry environments, and some of which can go dormant themselves. Nematodes are usually microscopic with this lifestyle. Although eutardigrades only have lifespans of a few months, they famously can enter suspended animation during dry or hostile conditions and survive for decades, which allows them to be ubiquitous in terrestrial environments despite needing water to grow and reproduce. Many microscopic crustacean groups likecopepodsandamphipodsandseed shrimpsare known to go dormant when dry and live in transient bodies of water too.

See also

• Aquatic animal
• Aquatic ecosystem
• Aquatic locomotion
• Aquatic mammal
• Aquatic plant
• Marine invertebrates
• Marine mammal
• Terrestrial
• Terrestrial ecosystem
• Terrestrial locomotion
• Terrestrial plant
• Wetland– Type of land area that is flooded or saturated with water
• Wetland indicator status
• Zoology

Further reading

• Clack J. A.(2002).Gaining ground: the origin and evolution of tetrapods.Indiana University Press,369 pp.,ISBN978-0-253-34054-2.
• Cloudsley-Thompson J. L. (1988).Evolution and adaptation of terrestrial arthropods.Springer,141 pp.,ISBN978-3-540-18188-0.
• Dejours P. et al. (1987).Comparative physiology: life in water and on land.Liviana Editrice, Italy, 556 pp.,ISBN978-0-387-96515-4.
• Gordon M. S. & Olson E. C. (1995).Invasions of the land: the transitions of organisms from aquatic to terrestrial life.Columbia University Press,312 pp.,ISBN978-0-231-06876-5.
• Little C. (1983).The colonisation of land: Origins and adaptations of terrestrial animals.Cambridge University Press,Cambridge. 290 pp.,ISBN978-0-521-25218-8.
• Little C. (1990).The terrestrial invasion. An ecophysiological approach to the origin of land animals.Cambridge University Press, Cambridge. 304 pp.ISBN978-0-521-33669-7.
• Zimmer, Carl (1999).At the Water's Edge: Fish with Fingers, Whales with Legs, and How Life Came Ashore but Then Went Back to Sea.New York: Touchstone.ISBN0684856239.

References

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