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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 ...
More than 99 percent of all species, amounting to over five billion species, [7] that ever lived on Earth are estimated to be extinct. [8] [9] Estimates on the number of Earth's current species range from 10 million to 14 million, [10] of which about 1.2 million have been documented and over 86 percent have not yet been described. [11]
In 2008, WoRMS stated that it hoped to have an up-to-date record of all marine species completed by 2010, the year in which the Census of Marine Life was completed. [4] As of February 2018, WoRMS contained listings for 480,931 marine species names (including synonyms) of which 247,000 are valid marine species (98% checked).
Anisakis species parasitise fish, and marine mammals and when consumed by humans can cause anisakiasis a gastric or gastroallergic disease. [68] Gastrointestinal nematode infections in humans are common, with approximately 50% of the global population being affected.
[36] [37] The compound eyes probably evolved independently of arthropods' eyes. [23] Some tube-worms use ocelli widely spread over their bodies to detect the shadows of fish, so that they can quickly withdraw into their tubes. [36] Some burrowing and tube-dwelling polychaetes have statocysts (tilt and balance sensors) that indicate which way is ...
Arthropoda is the largest animal phylum with the estimates of the number of arthropod species varying from 1,170,000 to 5~10 million and accounting for over 80 percent of all known living animal species. [36] [37] One arthropod sub-group, the insects, includes more described species than any other taxonomic class. [38] The total number of ...
From a total of around 7,000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms. [ 49 ] Of the 182 taxa of earthworms found in the United States and Canada, 60 (33%) are introduced species.
Marine arthropods range in size from the microscopic crustacean Stygotantulus to the Japanese spider crab. Arthropods' primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph - analogue of blood - circulates; they have open circulatory systems. Like their exteriors, the internal organs ...