Overview
Priapulida (priapulid worms or penis worms, from Gr. p???p??, priapos 'Priapus' + Lat. -ul-, diminutive) is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis. They live in the mud, which they eat, in comparatively shallow waters up to 90 metres (300 ft).
Together with Echiura and Sipuncula, they were once placed in the taxon Gephyrea, but it is now clear that they belong to Ecdysozoa, which mostly include microscopic animals, with the exception of the relatively large arthropods, velvet worms, and the priapulids. Their nearest relatives are probably Kinorhyncha and Loricifera with which they constitute the taxon Scalidophora.2] They feed on slow-moving invertebrates, such as polychaete worms.
Priapulid-like fossils are known at least as far back as the Middle Cambrian. They were likely major predators of the Cambrian period. However, crown-group priapulids cannot be recognized until the Carboniferous.[1] Only sixteen extant species of priapulid worms are known.
Anatomy
Priapulids are cylindrical worm-like animals, ranging from 0.5 to 20 centimetres (0.20 to 7.9 in) in length, with a median anterior mouth quite devoid of any armature or tentacles. The body is divided into a main trunk or abdomen and a somewhat swollen proboscis region ornamented with longitudinal ridges. The body is ringed and often has circles of spines, which are continued into the slightly protrusible pharynx. Some species may also have a tail or a pair of caudal appendages. The body has a chitinous cuticle that is moulted as the animal grows.[3]
There is a wide body-cavity, it has no connection with the renal or reproductive organs, so it is not a coelom; it is probably a blood-space or hemocoel. There are no vascular or respiratory systems, but the body cavity does contain phagocytic amoebocytes and cells containing the respiratory pigment haemerythrin.[3]
The alimentary canal is straight, consisting of an eversible pharynx, an intestine, and a short rectum. The pharynx is muscular and lined by teeth.[3] The anus is terminal, although in Priapulus one or two hollow ventral diverticula of the body-wall stretch out behind it.
The nervous system comprises a nerve ring around the pharynx and a single ventral cord running the length of the body and including a number of ganglia. It retains its primitive connection with the ectoderm, forming part of the body wall. There are no specialized sense organs, but there are sensory nerve endings in the body, especially on the proboscis.[3]
The priapulids are gonochoristic, having two separate sexes (i.e male and female)[4] Their male and female organs are closely associated with the excretory protonephridia. They comprise 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 like those found in flatworms and other animals, and these probably function as excretory organs. As the animals mature, diverticula arise on the tubes of these organs, which develop either spermatozoa or ova. These sex cells pass out through the ducts.
Reproduction and development
Nothing is known of development, although the eggs hatch and go through development stages that resemble adults,[5] with a vague superficial resemblance to rotifers.[3] Some newly hatched larvae lack a proper lorica. Priapulidae hatching morphology includes these features: light-bulb shape; subdivided into introvert, neck and trunk; lacking a true lorica; without a mouth; without pharyngeal teeth; armed with seven or more scalids; and with four posterior tubuli.[6]
Fossil record
Stem-group Priapulids are known from the Middle Cambrian Burgess shale, where their soft-part anatomy is preserved, often in conjunction with their gut contents ? allowing a reconstruction of their diets.[7] Trace fossils that are morphologically almost identical to the burrows (Treptichnus pedum) officially mark the start of the Cambrian period, suggesting that priapulids, or at least close anatomical relatives, evolved around this time.[7]
Classification
Uncertain relationship
Stem-group Priapulida
- Class ?Archaeopriapulida
- Genus ?Ancalagon
- Genus ?Anningvermis
- Genus ?Corynetis
- Genus ?Ottoia
- and more...
Phylum Priapulida
- Class Priapulimorpha
- Order Priapulimorphida
- Family Priapulidae
- Genus Acanthopriapulus
- Genus Priapulopsis
- Genus Priapulus
- Family Tubiluchidae
- Genus Meiopriapulus
- Genus Tubiluchus
- Family Priapulidae
- Order Priapulimorphida
- Class Halicryptomorpha
- Order Halicryptomorphida
- Family Halicryptidae
- Genus Halicryptus
- Family Halicryptidae
- Order Halicryptomorphida
- Class Seticoronaria
- Order Seticoronarida
- Family Maccabeidae
- Genus Maccabeus
- Family Maccabeidae
- Order Seticoronarida
Reproduction and development
Nothing is known of development, although the eggs hatch and go through development stages that resemble adults,[5] with a vague superficial resemblance to rotifers.[3] Some newly hatched larvae lack a proper lorica. Priapulidae hatching morphology includes these features: light-bulb shape; subdivided into introvert, neck and trunk; lacking a true lorica; without a mouth; without pharyngeal teeth; armed with seven or more scalids; and with four posterior tubuli.[6]
Fossil record
Stem-group Priapulids ar e known from the Middle Cambrian Burgess shale, where their soft-part anatomy is preserved, often in conjunction with their gut contents ? allowing a reconstruction of their diets.[7] Trace fossils that are morphologically almost identical to the burrows (Treptichnus pedum) officially mark the start of the Cambrian period, suggesting that priapulids, or at least close anatomical relatives, evolved around this time.[7]
Classification
Uncertain relationship
Stem-group Priapulida
- Class ?Archaeopriapulida
- Genus ?Ancalagon
- Genus ?Anningvermis
- Genus ?Corynetis
- Genus ?Ottoia
- and more...
Phylum Priapulida
- Class Priapulimorpha
- Order Priapulimorphida
- Family Priapulidae
- Genus Acanthopriapulus
- Genus Priapulopsis
- Genus Priapulus
- Family Tubiluchidae
- Genus Meiopriapulus
- Genus Tubiluchus
- Family Priapulidae
- Order Priapulimorphida
- Class Halicryptomorpha
- Order Halicryptomorphida
- Family Halicryptidae
- Genus Halicryptus
- Family Halicryptidae
- Order Halicryptomorphida
- Class Seticoronaria
- Order Seticoronarida
- Family Maccabeidae
- Genus Maccabeus
- Family Maccabeidae
- Order Seticoronarida
References
- ^ a b Budd, G. E.; Jensen, S. R. (2007). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews 75: 253. doi:10.1111/j.1469-185X.1999.tb00046.x. edit
- ^ Dunn, Casey W; Andreas Hejnol, David Q. Matus, Kevin Pang, William E. Browne, Stephen A. Smith, Elaine Seaver, Greg W. Rouse, Matthias Obst, Gregory D. Edgecombe, Martin V. S?rensen, Steven H. D. Haddock, Andreas Schmidt-Rhaesa, Akiko Okusu, Reinhardt M?bjerg Kristensen, Ward C. Wheeler, Mark Q. Martindale, Gonzalo Giribet (2008-04). "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature 452 (7188): 745?749. doi:10.1038/nature06614. ISSN 0028-0836. PMID 18322464.
- ^ a b c d e Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 873?877. ISBN 0-03-056747-5.
- ^ Pechenik, Jan (2010). Biology of the Invertebrates. New York: McGraw-hill. pp. 454. ISBN 9870073028262.
- ^ Pechenik, Jan (2010). Biology of the Invertebrates. New york: McGraw-hill. pp. 454. ISBN 9780073028262.
- ^ The hatching larva of the priapulid worm Halicryptus spinulosus by Ralf Janssen, Sofia A Wennberg, and Graham E Budd
- ^ a b Vannier, J.; Calandra, I.; Gaillard, C.; Zylinska, A. (2010). "Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary". Geology 38 (8): 711?714. doi:10.1130/G30829.1. http://geology.gsapubs.org/cgi/content/abstract/38/8/711. edit
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclop?dia Britannica (11th ed.). Cambridge University Press.
External links
- "Evolution of a penis worm". University of Bristol. 2006-08-09. http://www.bris.ac.uk/news/2006/1052.html.
- Play It Again, Life: Natural History, February 1986
Taxonomy
The Phylum Priapulida is a member of the Superphylum Aschelminthes. Here is the complete "parentage" of Priapulida:
- Domain: Eukaryota
- eukaryotes
- Kingdom: Animalia
C. Linnaeus, 1758 - animals
- Subkingdom: Bilateria
(Hatschek, 1888) Cavalier-Smith, 1983 - bilaterians
- Branch: Protostomia
Grobben, 1908 - protostomes
- Infrakingdom: Ecdysozoa
A.M.A. Aguinaldo et al., 1997 ex T. Cavalier-Smith, 1998 - ecdysozoans
- Superphylum: Aschelminthes
- Phylum: Priapulida Théel, 1906 - Priapulids
- Superphylum: Aschelminthes
- Infrakingdom: Ecdysozoa
A.M.A. Aguinaldo et al., 1997 ex T. Cavalier-Smith, 1998 - ecdysozoans
- Branch: Protostomia
Grobben, 1908 - protostomes
- Subkingdom: Bilateria
(Hatschek, 1888) Cavalier-Smith, 1983 - bilaterians
- Kingdom: Animalia
C. Linnaeus, 1758 - animals
The Phylum Priapulida is further organized into finer groupings including:
- Class (3): Halicryptomorpha · Priapulimorpha · Seticoronaria
- Species: ZipcodeZoo has pages for 25 species and subspecies in the Phylum Priapulida.
Classes
Halicryptomorpha
Priapulimorpha
Priapulimorphida is the sole order within the Priapulimorpha, one of the three extant Priapulid classes. [more]
Seticoronaria
More info about the Class Seticoronaria may be found here.
References
- ^ a b Budd, G. E.; Jensen, S. R. (2007). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews 75: 253. doi:10.1111/j.1469-185X.1999.tb00046.x. edit
- ^ Dunn, Casey W; Andreas Hejnol, David Q. Matus, Kevin Pang, William E. Browne, Stephen A. Smith, Elaine Seaver, Greg W. Rouse, Matthias Obst, Gregory D. Edgecombe, Martin V. S?rensen, Steven H. D. Haddock, Andreas Schmidt-Rhaesa, Akiko Okusu, Reinhardt M?bjerg Kristensen, Ward C. Wheeler , Mark Q. Martindale, Gonzalo Giribet (2008-04). "Broad phylogenomic sampling improves resolution of the animal tree of life". Nature 452 (7188): 745?749. doi:10.1038/nature06614. ISSN 0028-0836. PMID 18322464.
- ^ a b c d e Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 873?877. ISBN 0-03-056747-5.
- ^ Pechenik, Jan (2010). Biology of the Invertebrates. New York: McGraw-hil l. pp. 454. ISBN 9870073028262.
- ^ Pechenik, Jan (2010). Biology of the Invertebrates. New york: McGraw-hill. pp. 454. ISBN 9780073028262.
- ^ The hatching larva of the priapulid worm Halicryptus spinulosus by Ralf Janssen, Sofia A Wennberg, and Graham E Budd
- ^ a b Vannier, J.; Calandra, I.; Gaillard, C.; Zylinska, A. (2010). "Priapulid worms: Pioneer horizontal burrowers at the Precambrian-Cambrian boundary". Geology 38 (8): 711?714. doi:10.1130/G30829.1. http://geology.gsapubs.org/cgi/content/abstract/38/8/711. edit
Sources
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