Priapulida (priapulid worms or penis worms, from Gr. priāpos 'Priapus' + Lat. -ul-, diminutive) are a phylum of marine worms with an extensible spiny proboscis. Priapulid fossils are known at least as far back as the Middle Cambrian. Their nearest relatives are probably Kinorhyncha and Loricifera with which they constitute the taxon Scalidophora. Besides arthropods and velvet worms, it is only among Priapulida that we can find members of the Ecdysozoa which are relatively large in size. They were likely the major predators of the Cambrian period. There are 16 known species of Priapulid worms. Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... For other uses, see Animal (disambiguation). ... Bronze sculpture of Priapus making an offering to his phallus, House of the Vettii, Pompeii Fresco of Priapus, House of the Vettii, Pompeii. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... A worm is an elongated, slender, soft-bodied invertebrate animal. ... In general, a proboscis (from Greek pro before and boskein to feed) is an elongated appendage from the head of an animal. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... Orders Cyclorhagida Homalorhagida Kinorhyncha (Gr. ... Loricifera is a small phylum of marine sediment-dwelling animals with about a dozen known species. ... Scalidophora is a group of marine pseudocoelomate invertebrates, consisting of the three phyla Kinorhyncha, Priapulida, and Loricifera. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ... Genera Peripatus . ... Phyla Panarthropoda (6,181,000-10,193,000+ species)   Onychophora (200 species)   Tactopoda   Tardigrada (1,000+ species)   Arthropoda (6,180,000-10,192,000+ species) Scalidophora (288 species)   Priapulida (16 species)   Kinorhyncha (150 species)   Loricifera (122 species) Nematoda (20,000+ species) Nematomorpha (320 species) The Ecdysozoa are a group of...

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. The nervous system, composed of a ring and a ventral cord, retains its primitive connection with the ectoderm. For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... The Human Nervous System A human being coordinates its nervous system, the activity of the muscles, monitors the organs, constructs and also stops input from the senses, and initiates actions. ... The ectoderm is outermost of the three germ layers of the developing embryo, the other two being the mesoderm and the endoderm. ...

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 or hemocoel. Senses are the physiological methods of perception. ... In biology, an organ (Latin: organum, instrument, tool) is a group of tissues that perform a specific function or group of functions. ... Diagram of the human circulatory system. ... The Respiratory System Among four-legged animals, the respiratory system generally includes tubes, such as the bronchi, used to carry air to the lungs, where gas exchange takes place. ... Single Oxygenated Hemerythrin protein Trimeric Hemerythrin Protein Complex Hemerythrin (also spelled haemerythrin; from Greek words αίμα = blood and ερυθρός = red) is an oligomeric protein responsible for oxygen (O2) transportation in the marine invertebrate phyla of sipunculids, priapulids, brachiopods, and in a single annelid worm, magelona. ... A Hemocoel is a cavity or series of spaces between the organs of organisms with open circulatory systems like most arthropods and mollusks. ...

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 1st-century BC sculpture The Reclining Hermaphrodite, in the Museo Nazionale Romano, Palazzo Massimo Alle Terme in Rome A hermaphrodite is an organism that possesses both male and female sex organs during its life. ...

The tips of these tufts enclose a flame-cell similar to those found in flatworms 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 50 fathoms (90 m). Classes Monogenea Trematoda Cestoda Turbellaria Wikimedia Commons has media related to: Platyhelminthes Wikispecies has information related to: Platyhelminthes The flatworms (Phylum Platyhelminthes from the Greek platy, meaning flat and helminth, meaning worm) are a phylum of relatively simple soft-bodied invertebrate animals. ... A fathom is the name of a unit of length in the Imperial system (and the derived U.S. customary units). ...

Classification

Phylum Priapulida

Genus †Ancalagon

Genus †Anningvermis

Genus †Corynetis

Genus †Ottoia

Class Priapulimorpha

Order Priapulimorphida

Family Priapulidae

Genus Acanthopriapulus

Genus Priapulopsis

Genus Priapulus

Family Tubiluchidae

Genus Meiopriapulus

Genus Tubiluchus

Class Halicryptomorpha

Order Halicryptomorphida

Family Halicryptidae

Genus Halicryptus

Class Seticoronaria

Order Seticoronarida

Family Maccabeidae

Genus Maccabeus

External links

• Paul Marks. "X-rays break the silence of ancient worms", New Scientist, 2006-08-09. 
• "Evolution of a penis worm", University of Bristol, 2006-08-09. 

New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... Year 2006 (MMVI) was a common year starting on Sunday (link displays full 2006 calendar) of the Gregorian calendar. ... is the 221st day of the year (222nd in leap years) in the Gregorian calendar. ... The University of Bristol is a university in Bristol, England. ... Year 2006 (MMVI) was a common year starting on Sunday (link displays full 2006 calendar) of the Gregorian calendar. ... is the 221st day of the year (222nd in leap years) in the Gregorian calendar. ...

References

• This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

Encyclopædia Britannica, the eleventh edition The Encyclopædia Britannica Eleventh Edition (1910–1911) is perhaps the most famous edition of the Encyclopædia Britannica. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ...