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The Myzostomida or Myzostomatida are an order of small marine worms, which are Parasitism on , mostly . These highly unusual and diverse annelids were first discovered by Friedrich Sigismund Leuckart in 1827.
Full-grown myzostomids are . Their internal organs consist of a branched sac opening to the exterior or each side. The paired ovaries discharge their eggs into a median chamber with side branches, often called the uterus, from which the ripe ova (eggs) are discharged by a mediar dorsal pore into the end of the rectum.
Fridtjof Nansen wrote in 1885 the thesis Bidrag til myzostomernes anatomi og histologi[1] Bidrag til myzostomernes anatomi og histologi on the Myzostomida.
According to the World Register of Marine Species, these families and genus are accepted in this group:
Biology
Some species, such as Myzostoma cirriferum, move about on the host; others, such as Myzostoma glabrum, remain stationary with the pharynx inserted in the mouth of the crinoid. Myzostoma deformator gives rise to a gall on the arm of the host, one joint of the pinnule growing round the worm so as to enclose it in a cyst while Myzostoma pulvinar lives in the alimentary canal of a species of Antedon.
Classification
In the past Myzostomida have been regarded as close relatives of the trematode or of the , but in 1998 it was suggested that they are a sub-group of polychaetes. However, another analysis in 2002 suggested that myzostomids are more closely related to flatworms or to and acanthocephala. They are now thought to be annelids, while their relationship to other annelids is unclear.
Further reading
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