Threatened arthropods and described. The total number of living arthropod species is probably in the tens of millions. One conservative estimate puts the number of arthropod species in tropical forests alone at six to nine million species. As a consequence of all of the above, most published estimates of the total number of endangered insects and arachnids are probably low by at least an order of magnitude. Conservatively at least eighty percent of all living animal species are arthropods. Since arthropods constitute the majority of the faunal biomass on Earth, their role is vital to the survival of large numbers of insectivores
Arthropod gills that were very different from those of arthropods. This reasoning implies that "Parapeytoia", which has legs and a backward-pointing mouth like that of the earliest arthropods, is a more credible closest relative of arthropods than is "Anomalocaris". In 2006, they suggested that arthropods were more closely related to lobopods and tardigrades than to anomalocarids. In 2014, research indicated that tardigrades were more closely related to arthropods than velvet worms. Higher up the "family tree", the Annelida have traditionally been considered the closest relatives of the Panarthropoda, since both groups have segmented bodies, and the combination of these groups was