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The difference is that protonephridia combine both filtration stages in the same organ, while metanephridia perform only the second filtration and rely on other mechanisms for the first – in annelids special filter cells in the walls of the blood vessels let fluids and other small molecules pass into the coelomic fluid, where it circulates to ...
In roundworms and flatworms they serve as attachment between individuals particularly during mating. In annelids, a sucker can be both a functional mouth and a locomotory organ . [ 2 ] The structure and number of suckers are often used as basic taxonomic diagnosis between different species, since they are unique in each species.
About 90% of nematodes reside in the top 15 cm (6") of soil. Nematodes do not decompose organic matter, but, instead, are parasitic and free-living organisms that feed on living material. Nematodes can effectively regulate bacterial population and community composition—they may eat up to 5,000 bacteria per minute.
[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 ...
Earthworms have many internal parasites, including protozoa, platyhelminthes, mites, and nematodes; they can be found in the worms' blood, seminal vesicles, coelom, or intestine, or in their cocoons (e.g. the mite Histiostoma murchiei is a parasite of earthworm cocoons [53]).
These two groups have long been considered close relatives because of the common presence of trochophore larvae, but the annelids were considered closer to the arthropods because they are both segmented. [53] Now, this is generally considered convergent evolution, owing to many morphological and genetic differences between the two phyla. [54]
Dunn et al. in 2008 suggested that the tardigrada could be grouped along with the nematodes, leaving Onychophora as the sister group to the arthropods. [11] The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic in representing the primitive condition from which the ...
Like most annelids, with a few exceptions like Sipuncula, Echiura and Diurodrilus, [27] the leech is a segmented animal, but unlike other annelids, the segmentation is masked by secondary external ring markings . [28] The number of annulations varies, both between different regions of the body and between species. [24]