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Some roundworms are also parasites: the Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries. Annelida, consists of the segmented worms, with bodies divided into segments or rings. Among these worms are the earthworms and the bristle worms of the sea.
Although all arthropods use muscles attached to the inside of the exoskeleton to flex their limbs, some still use hydraulic pressure to extend them, a system inherited from their pre-arthropod ancestors; [59] for example, all spiders extend their legs hydraulically and can generate pressures up to eight times their resting level. [60]
[1] [2] Well-known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them. Together with the Deuterostomia and Xenacoelomorpha, these form the clade Bilateria, animals with bilateral symmetry, anteroposterior axis and three germ layers ...
Many have fluid-filled, hydrostatic skeletons, like jellyfish or worms. Others have hard exoskeletons , outer shells like those of insects and crustaceans . The most familiar invertebrates include the Protozoa , Porifera , Coelenterata , Platyhelminthes , Nematoda , Annelida , Echinodermata , Mollusca and Arthropoda .
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 ]
Arthropods are intermediate hosts of Hymenolepis nana, otherwise known as the "dwarf tapeworm," while humans are used as final hosts. Humans become infected and develop hymenolepiasis through eating infected arthropods, ingesting eggs in water inhabited by arthropods, or from dirty hands. This is a common and widespread intestinal worm. [5]
Having two pairs of legs by segments, like millipedes, affected its locomotion and implies it was a rather slow arthropod," Lhéritier said. Other examples of Carboniferous arthropod gigantism ...
For example, The British palaeontologist Graham Budd sees the Lobopodia as representing a basal grade from which the phyla Onychophora and Arthropoda arose, with Aysheaia comparable to the ancestral plan, and with forms like Kerygmachela and Pambdelurion representing a transition that, via the dinocaridids, would lead to an arthropod body plan ...