- Priapulida
Taxobox
name = Priapulida
regnum =Animal ia
phylum = Priapulida
phylum_authority = Théel, 1906Priapulida (priapulid worms or penis worms, from Gr. πριάπος, "priāpos" '
Priapus ' + Lat. "-ul-", diminutive) are a phylum of marineworm s with an extensible spinyproboscis . Priapulid fossils are known at least as far back as the MiddleCambrian . Their nearest relatives are probablyKinorhyncha andLoricifera with which they constitute the taxonScalidophora . Besidesarthropod s andvelvet worm s, it is only among Priapulida that we can find members of theEcdysozoa which are relatively large in size. They were likely the major predators of the Cambrian period. There are 16 known species of Priapulid worms.They are cylindrical worm-like animals, with a median anterior mouth quite devoid of any armature or tentacles. The body is ringed, and often has circles of spines, which are continued into the slightly protrusible pharynx. The
alimentary canal is straight, the anus terminal, though in "Priapulus" one or two hollow ventral diverticula of the body-wall stretch out behind it. Thenervous system , composed of a ring and a ventral cord, retains its primitive connection with theectoderm .There are no specialized
sense organs or vascular or respiratory systems (hemerythrin is the protein responsible for oxygen transportation). There is a wide body-cavity, but as this has no connection with the renal or reproductive organs it cannot be regarded as a coelom, but probably is a blood-space orhemocoel .The Priapuloidea are hermaphroditic, and their male and female organs, which are one with the excretory organs, consist of a pair of branching tufts, each of which opens to the exterior on one side of the anus.
The tips of these tufts enclose a flame-cell similar to those found in
flatworm s and other animals, and these probably function as excretory organs. As the animals become adult, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova. These pass out through the ducts. Nothing is known of the development. There are three genera: (i.) "Priapulus", with the species "P. caudatus" Lam. of the Arctic Mouth, surrounded by spines, and Antarctic and neighboring cold seas, and "P. bicaudatus", Dan., of the north Atlantic and Arctic seas; (ii.) "Priapuloides australis", de Guerne, of the southern circumpolar waters; and (iii.) "Halicryptus", with the species "H. spinulosus", v. Sieb., of northern seas. They live in the mud, which they eat, in comparatively shallow waters up to 50fathom s (90 m).Classification
Phylum Priapulida:::: Genus †"Ancalagon":::: Genus †"
Anningvermis ":::: Genus †"Corynetis ":::: Genus †"Ottoia ": ClassPriapulimorpha :: OrderPriapulimorphida ::: FamilyPriapulidae :::: Genus "Acanthopriapulus ":::: Genus "Priapulopsis ":::: Genus "Priapulus "::: FamilyTubiluchidae :::: Genus "Meiopriapulus ":::: Genus "Tubiluchus ": ClassHalicryptomorpha :: OrderHalicryptomorphida ::: FamilyHalicryptidae :::: Genus "Halicryptus ": ClassSeticoronaria :: OrderSeticoronarida ::: FamilyMaccabeidae :::: Genus "Maccabeus"External links
*cite news |publisher=
New Scientist |url=http://www.newscientisttech.com/article.ns?id=mg19125645.600&feedId=online-news_rss20 |title=X-rays break the silence of ancient worms |author=Paul Marks |date=2006-08-09
*cite news|publisher=University of Bristol |url=http://www.bris.ac.uk/news/2006/1052.html |title=Evolution of a penis worm |date=2006-08-09 References
*1911
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