Sipuncula

Last updated

Sipuncula
Temporal range: Cambrian–Recent
Thysanocardia nigra.jpg
Thysanocardia nigra
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Annelida
Class: Sipuncula
Rafinesque, 1814
Subclasses, orders and families

The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms. The name Sipuncula is from the genus name Sipunculus , and comes from the Latin siphunculus meaning a "small tube". [1]

Contents

Sipuncula was once considered a phylum, but was demoted to a class of Annelida, based on recent molecular work. [2]

Sipunculans vary in size but most species are under 10 cm (4 in) in length. The body is divided into an unsegmented, bulbous trunk and a narrower, anterior section, called the "introvert", which can be retracted into the trunk. The mouth is at the tip of the introvert and is surrounded in most groups by a ring of short tentacles. With no hard parts, the body is flexible and mobile. Although found in a range of habitats throughout the world's oceans, the majority of species live in shallow water habitats, burrowing under the surface of sandy and muddy substrates. Others live under stones, in rock crevices or in other concealed locations.

Most sipunculans are deposit feeders, extending the introvert to gather food particles and draw them into the mouth, and retracting the introvert when feeding conditions are unsuitable or danger threatens. With a few exceptions, reproduction is sexual and involves a planktonic larval stage. Sipunculid worms are used as food in some countries in south-east Asia.

Taxonomy

The Swedish naturalist Carl Linnaeus first described the worm Sipunculus nudus in his Systema naturae in 1767. [3] In 1814, the French zoologist Constantine Samuel Rafinesque used the word "Sipuncula" to describe the family (now Sipunculidae), [4] and in time, the term came to be used for the whole class. [5] This is a relatively understudied group, and it is estimated there may be around 162 species worldwide. [6]

The phylogenetic placement of this group in the past has proved troublesome. Originally classified as annelids, despite the complete lack of segmentation, bristles and other annelid characters, the phylum Sipuncula was later allied with the Mollusca, mostly on the basis of developmental and larval characters. These phyla have been included in a larger group, the Lophotrochozoa, that also includes the annelids, the ribbon worms and several other phyla. Phylogenetic analyses based on 79 ribosomal proteins indicated a position of Sipuncula within Annelida. [7] [8] Subsequent analysis of the mitochondrion's DNA has confirmed their close relationship to the Annelida (including echiurans and pogonophorans). [2] It has also been shown that a rudimentary neural segmentation similar to that of annelids occurs in the early larval stage, even if these traits are absent in the adults. [9]

Anatomy

Themiste petricola, everted.jpg
Themiste petricola, retracted.jpg
A sipunculan with introvert everted (left) and retracted

Sipunculans are worms ranging from 2 to 720 mm (0.1 to 28.3 in) in length, with most species being under 10 cm (4 in). The sipunculan body is divided into an unsegmented, bulbous trunk and a narrower, anterior section, called the "introvert". Sipunculans have a body wall somewhat similar to that of annelids (though unsegmented) in that it consists of an epidermis without cilia overlain by a cuticle, an outer layer of circular and an inner layer of longitudinal musculature. The body wall surrounds the coelom (body cavity) that is filled with fluid on which the body wall musculature acts as a hydrostatic skeleton to extend or contract the animal. When threatened, Sipunculid worms can contract their body into a shape resembling a peanut kernel—a practice that has given rise to the name "peanut worm". The introvert is pulled inside the trunk by two pairs of retractor muscles that extend as narrow ribbons from the trunk wall to attachment points in the introvert. It can be protruded from the trunk by contracting the muscles of the trunk wall, thus forcing the fluid in the body cavity forwards. [10] The introvert can vary in size from half the length of the trunk to several times its length, but whatever their comparative sizes, it is fully retractable. [11]

The mouth is located at the anterior end of the animal; in the subclass Sipunculidea, the mouth is surrounded by a mass of 18 to 24 ciliated tentacles, while in the subclass Phascolosomatidea, the tentacles are arranged in an arc above the mouth, surrounding the nuchal organ, also located at the tip of the introvert. The tentacles each have a deep groove along which food is moved to the mouth by cilia. [11] They are used to gather organic detritus from the water or substrate, and probably also function as gills. In the family Themistidae the tentacles form an elaborate crown-like structure, the members of this group being specialized filter feeders, unlike the other groups of sipunculans which are deposit feeders. [12] The tentacles are hollow and are extended via hydrostatic pressure in a similar manner as the introvert, but have a different mechanism from that of the rest of the introvert, being connected, via a system of ducts, to one or two contractile sacs next to the oesophagus. [10] Hooks are often present near the mouth on the introvert. These are proteinaceous, non-chitinous specializations of the epidermis, either arranged in rings or scattered. [11] They may be involved in scraping algae off rock, or alternatively provide anchorage. [13]

Three genera (Aspidosiphon, Lithacrosiphon and Cloeosiphon) in the Aspidosiphonidae family possess epidermal structures, known as anal and caudal shields. These are patches of thickened, hard plates, and are used for boring into rock; the anal shield is near the anteriorly-located anus on the trunk, just below the introvert of the animal, while the caudal shield is at the posterior of the body. [13] In Aspidosiphon and Lithacrosiphon the anal shield is restricted to the dorsal side, causing the introvert to emerge at an angle, whereas it surrounds the anterior trunk in Cloeosiphon with the introvert emerging from its center. In Aspidosiphon the shield is a hardened, horny structure; in Lithacrosiphon it is a calcareous cone; in Cloeosiphon it is composed of separate plates. When the introvert is retracted in these animals, the anal shield blocks the entrance to its burrow. At the posterior end of the trunk, a hardened caudal shield is sometimes present in Aspidosiphon; [14] this may help with anchoring the animal in its burrow or may be used in the boring process. [11]

Digestive system

The digestive tract of sipunculans starts with the esophagus, located between the introvert retractor muscles. In the trunk the intestine runs posteriorly, forms a loop and turns anteriorly again. The downward and upward sections of the gut are coiled around each other, forming a double helix. At the termination of the gut coil, the rectum emerges and ends in the anus, located in the anterior third of the trunk. Digestion is extra-cellular, taking place in the lumen of the intestine. A rectal caecum, present in most species, is a blind ending sac at the transition between intestine and rectum with unknown function. The anus is often not visible when the introvert is retracted into the trunk. [10]

Circulation

Sipunculans do not have a vascular blood system. Fluid transport and gas exchange are instead accomplished by the coelom, which contains the respiratory pigment haemerythrin, and the separate tentacular system, the two being separated by an elaborate septum. The coelomic fluid contains five types of coelomic cells: haemocytes, granulocytes, large multinuclear cells, ciliated urn-shaped cells and immature cells. The ciliated urn cells may also be attached to the peritoneum and assist in waste filtering from the coelomic fluid. Nitrogenous waste is excreted through a pair of metanephridia opening close to the anus, except in Phascolion and Onchnesoma, which have only a single nephridium. [10] A ciliated funnel, or nephrostome, opens into the coelomic cavity at the anterior end, close to the nephridiopore. The metanephridia have an osmoregulation function but it is unclear whether the mechanism is via filtration or secretion. They also serve as gamete storage and maintenance organs. [11]

The tentacular coelom connects the tentacles at the tip of the introvert to a ring canal at their base, from which a contractile vessel runs along beside the esophagus and ends blindly posteriorly. Some evidence points towards the involvement of these structures in ultrafiltration. [15] In crevice-dwelling sipunculans, respiration is mainly through the tentacular system, with oxygen diffusing into the trunk coelom from the tentacular coelom. However, in other species the skin is thin and respiration is mainly through the cuticle of the trunk, where oxygen uptake is assisted by the presence of dermal coelomic canals just beneath the epidermis. [11] [16]

Nervous system

The nervous system consists of dorsal cerebral ganglion, brain above the oesophagus and a nerve ring around the oesophagus, which links the brain with the single ventral nerve cord that runs the length of the body. Lateral nerves lead off this to innervate the muscles of the body wall. [11]

In some species, there are simple light-sensitive ocelli associated with the brain. Two organs, likely functioning as a unit for chemoreception are located near its anterior margin; the non-ciliated cerebral organ, which possesses bipolar sensory cells, and the nuchal organ, located posterior to the brain. [10] Similar light-sensing tubes have been reported in the fauveliopsid annelids. [17] In addition, all sipunculans have numerous sensory nerve endings on the body wall, especially at the forward end of the introvert which is used for exploring the surrounding environment. [10]

Distribution and habitat

Sipunculus nudus Sipunculus nudus.jpeg
Sipunculus nudus

All sipunculid worms are marine and benthic; they are found throughout the world's oceans including polar waters, equatorial waters and the abyssal zone, but the majority of species occur in shallow water, where they are relatively common. They inhabit a range of habitats including burrowing in sand, mud, clay and gravel, hiding under stones, in rock crevices, in hollow coral heads, in wood, in empty seashells and inside the bones of dead whales. Some hide in kelp holdfasts, under tangles of eelgrass, inside sponges and in the empty tubes of other organisms, and some live among fouling organisms on man-made structures. [6] [18] Some bore into solid rocks to make a shelter for themselves. [19]

They are common below the surface of the sediment on tidal flats. These worms may stay submerged in the sea bed for between 10 and 18 hours a day. They are sensitive to low salinities, and thus not commonly found near estuaries. [19] They can also be abundant in coralline rock, and in Hawaii, up to seven hundred individuals have been found per square metre in burrows in the rock. [11]

Reproduction

Both asexual and sexual reproduction can be found in sipunculans, although asexual reproduction is uncommon and has only been observed in Aspidosiphon elegans and Sipunculus robustus . These reproduce asexually through transverse fission, followed by regeneration of vital body components, with S. robustus also reproducing by budding. [20] One species of sipunculan, Themiste lageniformis , has been recorded as reproducing parthenogenetically; eggs produced in the absence of sperm developed through the normal stages. [20]

Most sipunculan species are dioecious. Their gametes are produced in the coelomic lining, where they are released into the coelom to mature. These gametes are then picked up by the metanephridia system and released into the aquatic environment, where fertilisation takes place. [10] In at least one species, Themiste pyroides , swarming behaviour occurs with adults creating compact masses among rocks immediately before spawning. [18]

Although some species hatch directly into the adult form, many have a trochophore larva, which metamorphoses into the adult after anything from a day to a month, depending on species. In a few species, the trochophore does not develop directly into the adult, but into an intermediate pelagosphaera stage, that possesses a greatly enlarged metatroch (ciliated band). [21] Metamorphosis occurs only in the presence of suitable habitat conditions, and is triggered by the presence of adults. [22] [23]

Behaviour

Most sipunculans are deposit feeders employing a number of different methods to obtain their foods. Those living in burrows extend their tentacles over the surface of the sediment. Food particles get trapped in mucous secretions and the beating of cilia transport the particles to the mouth. Among those that burrow through the sand, the tentacles are replaced by fluted folds which scoop up sediment and food particles. Most of this material is swallowed but larger particles are discarded. Species dwelling in crevices are able to withdraw their introverts, blocking the crevice entrance with their thickened trunks and presumably ingesting any food they have snared at the same time. One species, Thysanocardia procera is thought to be carnivorous, gaining entrance in some way to the interior of the sea mouse Aphrodita aculeata and sucking out its liquefied contents. [18]

Fossil record

Lecthaylus gregarius, a sipunculan from the Silurian of Illinois. Lecthaylus gregarius 5.jpg
Lecthaylus gregarius, a sipunculan from the Silurian of Illinois.

Because of their soft-bodied structure, fossils of sipunculans are extremely rare, and are only known from a few genera. Archaeogolfingia and Cambrosipunculus appear in the Cambrian Chengjiang biota in China. These fossils appear to belong to the crown group, [24] [25] and demonstrate that sipunculans have changed little (morphologically) since the early Cambrian, about 520 million years ago. [24]

An unnamed sipunculid worm from the Cambrian period has been discovered in the Burgess Shale in Alberta, Canada, [26] and Lecthaylus has been identified from the Granton Shrimp Bed, near Edinburgh, Scotland, dating to the Silurian period. [27] Trace fossils of burrows that may have been formed by sipunculans have been found from the Paleozoic. [24]

Some scientists once hypothesized a close relationship between sipunculans and the extinct hyoliths, operculate shells from the Palaeozoic with which they share a helical gut; but this hypothesis has since been discounted. [28]

As food

Sipunculid worm jelly (土笋凍) is a delicacy in southeast China, originally from Anhai, near Quanzhou. [29] A sipunculid worm dish is also considered a delicacy in the islands of the Visayas region, Philippines. The muscle is first prepared by soaking it in spiced vinegar and then served with other ingredients as a dish similar to ceviche. It is a basic food for local fisherman and is sometimes seen in city restaurants as an appetizer. This style of food preparation is locally called kilawin or kinilaw, and is also used for fish, conch and vegetables. [30]

The worms, especially in dried form, are considered a delicacy in Vietnam as well, where they are caught on the coasts of Minh Chao island, in Van Don District. [30] The relatively high market price of the worms have made them a significant source of income for the local population of fishermen families. [19]

Related Research Articles

<span class="mw-page-title-main">Siboglinidae</span> Family of annelid worms

Siboglinidae is a family of polychaete annelid worms whose members made up the former phyla Pogonophora and Vestimentifera. The family is composed of about 100 species of vermiform creatures which live in thin tubes buried in sediments (Pogonophora) or in tubes attached to hard substratum (Vestimentifera) at ocean depths ranging from 100 to 10,000 m. They can also be found in association with hydrothermal vents, methane seeps, sunken plant material, and whale carcasses.

<span class="mw-page-title-main">Echiura</span> Group of marine animals ("spoon worms")

The Echiura, or spoon worms, are a small group of marine animals. Once treated as a separate phylum, they are now considered to belong to Annelida. Annelids typically have their bodies divided into segments, but echiurans have secondarily lost their segmentation. The majority of echiurans live in burrows in soft sediment in shallow water, but some live in rock crevices or under boulders, and there are also deep sea forms. More than 230 species have been described. Spoon worms are cylindrical, soft-bodied animals usually possessing a non-retractable proboscis which can be rolled into a scoop-shape to feed. In some species the proboscis is ribbon-like, longer than the trunk and may have a forked tip. Spoon worms vary in size from less than a centimetre in length to more than a metre.

<span class="mw-page-title-main">Prostomium</span>

The prostomium is the cephalized first body segment in an annelid worm's body at the anterior end. It is in front of the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. The prostomium together with the peristomium, which includes the mouth and pharynx, make up the annelid head.

Golfingia vulgaris is a marine invertebrate belonging to the phylum Sipuncula, the peanut worms. It is a cylindrical, unsegmented worm with a crown of tentacles around the mouth. It lives in burrows in shallow seas in various parts of the world.

<i>Sipunculus nudus</i>

Sipunculus nudus is a cosmopolitan species of unsegmented marine worm of the phylum Sipuncula, also known as peanut worms.

<span class="mw-page-title-main">Aspidosiphonidae</span> Family of peanut worms

Aspidosiphonidae is a family of peanut worms. It is the only family in the monotypic order Aspidosiphonida, which is in the class Phascolosomatidea.

Phascolopsis gouldii is a species of unsegmented benthic marine worm, also known as a peanut worm or star worm. It lives in burrows in muddy sand in shallow waters off North America.

<span class="mw-page-title-main">Cirratulidae</span> Family of annelid worms

Cirratulidae is a family of marine polychaete worms. Members of the family are found worldwide, mostly living in mud or rock crevices. Most are deposit feeders, but some graze on algae or are suspension feeders.

<span class="mw-page-title-main">Annelid</span> Phylum of segmented worms

The annelids, also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.

Nephasoma minutum is a marine invertebrate of the phylum Sipuncula, commonly known as peanut worms because of their shape when contracted. It is a cylindrical, unsegmented worm with a crown of tentacles around the mouth. These worms live in crevices in the rocks or in burrows in shallow water in Western Europe, and the eastern United States.

Nephasoma rimicola is a marine invertebrate belonging to the phylum Sipuncula, the peanut worms. This worm occurs in the northeastern Atlantic Ocean.

Phascolosoma granulatum is a species of peanut worm in the family Phascolosomatidae. It is found in shallow water in the northeastern Atlantic Ocean and the Mediterranean Sea.

<span class="mw-page-title-main">Bonelliidae</span> Family of annelid worms

Bonelliidae is a family of marine worms noted for being sexually dimorphic, with males being tiny in comparison with the females. They occupy burrows in the seabed in many parts of the world's oceans, often at great depths.

Aspidosiphon elegans is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms. It is a bioeroding species and burrows into limestone rocks, stones and corals. It occurs in the western Indo-Pacific region, the Red Sea, and the tropical western Atlantic Ocean, and is invasive in the eastern Mediterranean Sea.

<i>Aspidosiphon muelleri</i> Species of marine worm

Aspidosiphon muelleri is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms. This worm is found in the eastern Atlantic Ocean, the Mediterranean Sea and in various locations in the Indo-Pacific region at depths down to about 1,000 m (3,300 ft).

Themiste cymodoceae is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms. It is native to shallow waters around Australia and in the South China Sea where it lives in a cavity it creates among seagrass roots and in empty oyster shells.

Themiste hennahi is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms. It is native to shallow waters on the Pacific coast of North and South America. This worm was first described in 1828 by the British zoologist John Edward Gray as Themiste hennahi, the type specimen having been collected by the Rev. W. Hennah, with the type locality being Peru.

<i>Themiste pyroides</i> Species of worm

Themiste pyroides is a species of unsegmented benthic marine worm in the phylum Sipuncula, the peanut worms. It occurs in the intertidal zone and shallow water in the western Atlantic Ocean and the northeastern Pacific Ocean. It lives in crevices and under rocks, extending its "crown" of branching tentacles into the surrounding water to feed.

Thysanocardia procera is a marine invertebrate belonging to the phylum Sipuncula, the peanut worms. It is a cylindrical, unsegmented worm with a crown of tentacles around the mouth. It is native to shallow seas in the northeastern Atlantic Ocean.

<span class="mw-page-title-main">Tomopteridae</span>

Tomopteridae is a family of holopelagic polychaetes belonging to the order Phyllodocida. The genus Tomopteris consist of about 70 species, and the three other genera of one known species each. Length varies from just 1-2 cm to 30 cm. These are very active swimmers, and have some of the highest metabolic rate among annelids. To increase buoyancy they have a large body cavity (coelom) filled with body fluid of a density similar to seawater. With the coelom taking up much of the inner space, the muscular system has been reduced to a mesh just below the epidermis. The circulatory system has been lost, and the coelomic fluid has taken over the role of transporting oxygen, nutrients and gametes. Instead of a heart the inner surface of the worm is covered with cilia that moves the fluid around inside the body. The absence of septa between the segments makes the circulation more efficient. A series of extretory organs called metanephridia consists of ciliated funnels which opens to the coleomic cavity and connects with the exterior though a nephridiopore. Some species are bioluminescent, and produce a yellow light.

References

  1. "Sipuncula". Oxford Living Dictionaries. Oxford University Press. Archived from the original on 12 February 2019. Retrieved 10 February 2019.
  2. 1 2 Shen, X.; Ma, X.; Ren, J.; Zhao, F. (2009). "A close phylogenetic relationship between Sipuncula and Annelida evidenced from the complete mitochondrial genome sequence of Phascolosoma esculenta". BMC Genomics. 10: 136. doi:10.1186/1471-2164-10-136. PMC   2667193 . PMID   19327168.
  3. Saiz-Salinas, José (2009). "Sipunculus (Sipunculus) nudus Linnaeus, 1766". WoRMS. World Register of Marine Species . Retrieved 27 February 2019.
  4. Rafinesque, Constantine Samuel (1814). Précis des découvertes et travaux somiologiques de m.r C. S. Rafinesque-Schmaltz entre 1800 et 1814 ou Choix raisonné de ses principales découvertes en zoologie et en botanique. Royale typographie militaire, aux dépens de l'auteur. p.  32.
  5. "Sipuncula". WoRMS. World Register of Marine Species. 2018. Retrieved 27 February 2019.
  6. 1 2 Pancucci-Papadopoulou, M.A.; Murina, G.V.V.; Zenetos, A. (2014). "The phylum Sipuncula in the Mediterranean Sea" (PDF). National Centre for Marine Research. Archived from the original (PDF) on 12 February 2019. Retrieved 10 February 2019.
  7. Struck, T. H.; Paul, C.; Hill, N.; Hartmann, S.; Hösel, C.; Kube, M.; Lieb, B.; Meyer, A.; Tiedemann, R.; Purschke, G. N.; Bleidorn, C. (3 March 2011). "Phylogenomic analyses unravel annelid evolution". Nature. 471 (7336): 95–98. Bibcode:2011Natur.471...95S. doi:10.1038/nature09864. PMID   21368831. S2CID   4428998.
  8. Hausdorf, B.; et al. (2007). "Spiralian Phylogenomics Supports the Resurrection of Bryozoa Comprising Ectoprocta and Entoprocta". Molecular Biology and Evolution. 24 (12): 2723–2729. doi: 10.1093/molbev/msm214 . PMID   17921486.
  9. Wanninger, Andreas; Kristof, Alen; Brinkmann, Nora (January–February 2009). "Sipunculans and segmentation". Communicative and Integrative Biology. 2 (1): 56–59. doi:10.4161/cib.2.1.7505. PMC   2649304 . PMID   19513266.
  10. 1 2 3 4 5 6 7 Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 863–870. ISBN   978-0-03-056747-6.
  11. 1 2 3 4 5 6 7 8 Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 495–501. ISBN   978-81-315-0104-7.
  12. Cutler, Edward Bayler (1994). The Sipuncula: Their Systematics, Biology, and Evolution. Cornell University Press. p. 5. ISBN   978-0-8014-2843-2.
  13. 1 2 Australian Biological Resources Study (2000). Polychaetes & Allies: The Southern Synthesis. Csiro Publishing. p. 378. ISBN   978-0-643-06571-0.
  14. Schulze, A.; et al. (March 2005). "Reconstructing the phylogeny of the Sipuncula". Hydrobiologia. 535/536: 277–296. doi:10.1007/s10750-004-4404-3. S2CID   20948259.
  15. Pilger, J.F.; Rice, M.E. (1987). "Ultrastructural evidence for the contractile vessel of sipunculans as a possible ultrafiltration site". American Zoology. 27: 810a.
  16. Australian Biological Resources Study (2000). Polychaetes & Allies: The Southern Synthesis. Csiro Publishing. p. 383. ISBN   978-0-643-06571-0.
  17. Purschke, Günter (2011). "Sipunculid‐like ocellar tubes in a polychaete, Fauveliopsis cf. adriatica (Annelida, Fauveliopsidae): implications for eye evolution". Invertebrate Biology. 130 (2): 115–128. doi:10.1111/j.1744-7410.2011.00226.x.
  18. 1 2 3 Walls, Jerry G. (1982). Encyclopedia of Marine Invertebrates. TFH Publications. pp.  255–262. ISBN   978-0-86622-141-2.
  19. 1 2 3 Nguyen, Thi Thu Ha, et al. "The distribution of peanut-worm (Sipunculus nudus) in relation with geo-environmental characteristics." (2007).
  20. 1 2 Rice, Mary E.; Pilger, John F. (1988). "Sipuncula" (PDF). Archived from the original (PDF) on 5 May 2017. Retrieved 6 February 2019.
  21. Rice, M.E. (1976). "Larval development and metamorphosis in Sipuncula". American Zoologist. 16 (3): 563–571. doi: 10.1093/icb/16.3.563 .
  22. Pechenik, J.A.; Rice, M.E. (1990). "Influence of delayed metamorphosis on postsettlement survival and growth in the sipunculan Apionsoma misakianum". Invertebrate Biology. 120 (1): 50–57. doi:10.1111/j.1744-7410.2001.tb00025.x.
  23. Rice, M.E. (1986). "Factors influencing larval metamorphosis in Golfingia misakiana (Sipuncula)". Bulletin of Marine Science. 39 (2): 362–375.
  24. 1 2 3 Huang, D. -Y.; Chen, J. -Y.; Vannier, J.; Saiz Salinas, J. I. (22 August 2004). "Early Cambrian sipunculan worms from southwest China". Proceedings of the Royal Society B: Biological Sciences. 271 (1549): 1671–6. doi:10.1098/rspb.2004.2774. PMC   1691784 . PMID   15306286.
  25. Eibye-Jacobsen, D.; Vinther, J. (February 2012). "Reconstructing the ancestral annelid". Journal of Zoological Systematics and Evolutionary Research. 50: 85–87. doi:10.1111/j.1439-0469.2011.00651.x.
  26. Caron, J. -B.; Gaines, R. R.; Mangano, M. G.; Streng, M.; Daley, A. C. (2010). "A new Burgess Shale-type assemblage from the "thin" Stephen Formation of the southern Canadian Rockies". Geology. 38 (9): 811–814. Bibcode:2010Geo....38..811C. doi:10.1130/G31080.1.
  27. Muir, L. A.; Botting, J. P. (2007). "A Lower Carboniferous sipunculan from the Granton Shrimp Bed, Edinburgh". Scottish Journal of Geology. 43: 51–56. doi:10.1144/sjg43010051. S2CID   131119101.
  28. Moysiuk,Joseph; Smith, Martin R.; Caron, Jean-Bernard (2017). "Hyoliths are Palaeozoic lophophorates" (PDF). Nature. 541 (7637): 394–397. Bibcode:2017Natur.541..394M. doi:10.1038/nature20804. PMID   28077871. S2CID   4409157. Archived (PDF) from the original on 9 October 2022.
  29. Dorman, Jeremy Alban (16 December 2009). "Peanut worm jelly: It's what's for dinner". The Telegraph. Never yet melted. Archived from the original on 9 February 2019. Retrieved 9 February 2019.
  30. 1 2 "Women earn a living digging for peanut worms in northern Vietnam". Tuoi Tre News. 16 June 2018. Retrieved 9 February 2019.