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Free-living worm species do not live on land but instead live in marine or freshwater environments or underground by burrowing. In biology, "worm" refers to an obsolete taxon, Vermes, used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, now seen to be paraphyletic. The name stems from the Old English ...
Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (helminths) are the cause of soil-transmitted helminthiases. They are classified along with arthropods, tardigrades and other moulting animals in the clade Ecdysozoa.
These have about 4,500 species, [13] are mostly free-living, and range from 1 mm (0.04 in) to 600 mm (24 in) in length. Most are predators or scavengers, and terrestrial species are mostly nocturnal and live in shaded, humid locations, such as leaf litter or rotting wood.
The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantises, orthopterans, and crustaceans. [4] About 351 freshwater species are known [5] and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. [6] The name "Gordian" stems from the legendary Gordian ...
Planarians (triclads) are free-living flatworms of the class Turbellaria, [2] [3] order Tricladida, [4] which includes hundreds of species, found in freshwater, marine, and terrestrial habitats. [5] Planarians are characterized by a three-branched intestine, including a single anterior and two posterior branches. [5]
Gastrotricha are aquatic free-living worms, belonging to the benthic meiofauna. They have a high density in marine sediments and are often among top three of meiofauna found here, only surpassed by nematoda and harpacticoid Copepoda. The density of Gastrotrica can be as high as 364 individuals/10 cm2. [2]
The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic.There are about 4,500 species, which range from 1 mm (0.039 in) to large freshwater forms more than 500 mm (20 in) long [3] or terrestrial species like Bipalium kewense which can reach 600 mm (24 in) in length.
Rhabditida is an order of free-living, parasitic and microbivorous nematodes living in soil. The Cephalobidae , Panagrolaimidae , Steinernematidae , and Strongyloididae seem to be closer to the Tylenchia , regardless of whether these are merged with the Rhabditia or not.