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Priapulida (priapulid worms or penis worms, from Gr. p???p??, priapos 'Priapus
Priapus

In Greek mythology, Priapus was a minor rustic fertility god, protector of livestock, fruit plants, gardens and male genitalia. His Roman mythology equivalent was Mutinus Mutunus....
' + Lat. -ul-, diminutive) are a phylum of marine worm
Worm

A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms....
s with an extensible spiny proboscis
Proboscis

In general, a proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate..The correct Greek plural is proboscides, but in English it is more common to simply add -es, forming proboscises....
. Priapulid fossils are known at least as far back as the Middle Cambrian
Cambrian

The Cambrian is a geologic period that began about Mya at the end of the Proterozoic eon and ended about Ma with the beginning of the Ordovician period ....
. Their nearest relatives are probably Kinorhyncha
Kinorhyncha

Kinorhyncha is a phylum of small marine body cavity invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos....
 and Loricifera
Loricifera

Loricifera is a small phylum of marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more which have been collected and not yet described....
 with which they constitute the taxon Scalidophora
Scalidophora

Scalidophora is a group of marine body cavity invertebrates, consisting of the three phylum Kinorhyncha, Priapulida, and Loricifera. The members of the group share a number of characteristics, including introvert larvae and moulting of the cuticle ....
. Besides arthropod
Arthropod

Arthropods are animals belonging to the Scientific classification Arthropoda , and include the insects, arachnids, crustaceans, and others....
s and velvet worm
Velvet worm

The velvet worms form a clade within the Ecdysozoa and can be simply described as "worms with legs". Most common in the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting a sticky slime....
s, it is only among Priapulida that we can find members of the Ecdysozoa
Ecdysozoa

The Ecdysozoa are a grouping of protostome animals, including the Arthropoda , roundworm, and several smaller phylum . They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes....
 which are relatively large in size.






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Priapulida (priapulid worms or penis worms, from Gr. p???p??, priapos 'Priapus
Priapus

In Greek mythology, Priapus was a minor rustic fertility god, protector of livestock, fruit plants, gardens and male genitalia. His Roman mythology equivalent was Mutinus Mutunus....
' + Lat. -ul-, diminutive) are a phylum of marine worm
Worm

A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms....
s with an extensible spiny proboscis
Proboscis

In general, a proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate..The correct Greek plural is proboscides, but in English it is more common to simply add -es, forming proboscises....
. Priapulid fossils are known at least as far back as the Middle Cambrian
Cambrian

The Cambrian is a geologic period that began about Mya at the end of the Proterozoic eon and ended about Ma with the beginning of the Ordovician period ....
. Their nearest relatives are probably Kinorhyncha
Kinorhyncha

Kinorhyncha is a phylum of small marine body cavity invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos....
 and Loricifera
Loricifera

Loricifera is a small phylum of marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more which have been collected and not yet described....
 with which they constitute the taxon Scalidophora
Scalidophora

Scalidophora is a group of marine body cavity invertebrates, consisting of the three phylum Kinorhyncha, Priapulida, and Loricifera. The members of the group share a number of characteristics, including introvert larvae and moulting of the cuticle ....
. Besides arthropod
Arthropod

Arthropods are animals belonging to the Scientific classification Arthropoda , and include the insects, arachnids, crustaceans, and others....
s and velvet worm
Velvet worm

The velvet worms form a clade within the Ecdysozoa and can be simply described as "worms with legs". Most common in the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting a sticky slime....
s, it is only among Priapulida that we can find members of the Ecdysozoa
Ecdysozoa

The Ecdysozoa are a grouping of protostome animals, including the Arthropoda , roundworm, and several smaller phylum . They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes....
 which are relatively large in size. They were likely 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. The nervous system
Nervous system

The nervous system is a Neural network of specialized cells that communicate information about an animal's surroundings and itself. It processes this information and causes reactions in other parts of the body....
, composed of a ring and a ventral cord, retains its primitive connection with the ectoderm
Ectoderm

The ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.Generally speaking, the ectoderm differentiates to form the nervous system, Epidermis , and the outer part of integumentary system....
.

There are no specialized sense
Sense

Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception....
 organ
Organ (anatomy)

In biology, an organ is a biological tissue that performs a specific function or group of functions. Usually there is a main tissue and sporadic tissues....
s or vascular
Circulatory system

The circulatory system is an organ that moves nutrients, gases, and wastes to and from cells to help fight diseases and help stabilize body temperature and pH to maintain homeostasis....
 or respiratory
Respiratory system

A respiratory system?s function is to allow gas exchange. The space between the alveoli and the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism....
 systems (hemerythrin
Hemerythrin

Hemerythrin is an oligomeric protein responsible for oxygen transportation in the marine invertebrate Phylum of sipunculids, priapulids, brachiopods, and in a single annelid worm, magelona....
 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
Coelom

The coelom is a fluid filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages....
, but probably is a blood-space or hemocoel
Hemocoel

A hemocoel is a cavity or series of spaces between the organs of organisms with open circulatory systems, like most arthropods and mollusks. A combination of blood, lymph, and interstitial fluid called hemolymph circulates through the hemocoel....
.

The Priapuloidea are hermaphroditic
Hermaphrodite

A hermaphrodite is an organism having both male and female reproductive organs. In many species, hermaphroditism is a common part of the life-cycle, enabling a form of sexual reproduction in which partners are not separated into distinct male and female types of individual....
, 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
Flatworm

The flatworms, known in scientific literature as Platyhelminthes are a Phylum of relatively simple bilaterian, Segmentation , soft-bodied invertebrate animals....
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 50 fathom
Fathom

A fathom is a Units of measurement of length in the Imperial unit , used especially for measuring the depth of water.There are 2 yards in a fathom....
s (90 m).

Classification


Phylum Priapulida Genus †Ancalagon Genus †Anningvermis Genus †Corynetis Genus †Ottoia
Ottoia

Ottoia is among the largest and most abundant worms found in the fossils of the Cambrian Burgess Shale formation of British Columbia. It is an early Priapulida worm that averaged about 80mm in length....
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

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