Acorn worm

The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name.[1] Their closest relatives are the echinoderms.[2] There are 111 known species of acorn worm in the world,[3] the main species for research being Saccoglossus kowalevskii. Two families - Harrimaniidae and Ptychoderidae - separated at least 370 million years ago.[4]

Until recently, it was thought that all species lived in the sediment on the seabed, subsisting as deposit feeders or suspension feeders. However, the last decade has seen the description of a new family, the Torquaratoridae, evidently limited to the deep sea, in which most of the species crawl on the surface of the ocean bottom and alternatively rise into the water column, evidently to drift to new foraging sites.[5][6][7][8][9] It is assumed that the ancestors of acorn worms used to live in tubes like their relatives Pterobranchia, but that they eventually started to live a safer and more sheltered existence in sediment burrows instead.[10] Some of these worms may grow to be very long; one particular species may reach a length of 2.5 metres (8 ft 2 in), although most acorn worms are much smaller. Due to secretions containing elements like iodine, the animals have an iodoform-like smell.[11]

Acorn worms
Temporal range: 505–0 Ma
Enteropneusta
By Johann Wilhelm Spengel, 1893
Scientific classification
Kingdom: Animalia
Phylum: Hemichordata
Class: Enteropneusta
Gegenbaur, 1870
Order: Enteropneusta
Families

Anatomy

Balanoglossus 2
Structure of branchial region – bc, coelom. tb, tongue-bars. ds, mesentery. pr, ridge. vv, vessel. gp, gill-pore. dn, dorsal nerve. dv, vessel. œ, oesophagus. vs, mesentery. vn, ventral nerve.[12]
Balanoglossus 3
Structure of anterior end – a, Arrow from proboscis-cavity (pc) passing to left of pericardium (per) and out through proboscis pore-canal. b1, arrow from central canal of neurochord (cnc) passed out through anterior neuropore. b2, ditto; through posterior neuropore. c, arrow intended to pass from 1st gill-pouch through collar pore-canal into collar-coelom (cc). cts, posterior limit of collar. dv, dorsal vessel passing into central sinus (bs). ev, efferent vessel passing into ventral vessel (vv). epr, epiphysial tubes. st, stomochord. vs, ventral septum of proboscis. sk, body of nuchal skeleton. m, mouth. th, throat. tb, tongue-bars. tc, trunk coelom.[12]
Expn7526 (38827990315)
Acorn worm on the ocean floor

Most acorn worms range from 9 to 45 centimetres (3.5 to 17.7 in) in length, with the largest species, Balanoglossus gigas, reaching 1.5 metres (5 ft) or more. The body is made up of three main parts: an acorn-shaped proboscis, a short fleshy collar that lies behind it, and a long, worm-like trunk. The creature's mouth is located at the collar behind the proboscis.[13]

The skin is covered with cilia as well as glands that secrete mucus. Some produce a bromide compound that gives them a medicinal smell and might protect them from bacteria and predators. Acorn worms move only sluggishly, using ciliary action and peristalsis of the proboscis.[13]

Digestive system

Many acorn worms are detritus feeders, eating sand or mud and extracting organic detritus. Others feed on organic material suspended in the water, which they can draw into the mouth using the cilia on the gill bars.[14] A groove lined with cilia lies just in front of the mouth and directs suspended food into the mouth and may allow the animal to taste.[13]

The mouth cavity is tubular, with a narrow diverticulum or stomochord extending up into the proboscis. This diverticulum was once thought to be homologous with the notochord of chordates, hence the name "hemichordate" for the phylum. The mouth opens posteriorly into a pharynx with a row of gill slits along either side. The remainder of the digestive system consists of an oesophagus and intestine; there is no stomach.[13]

In some families there are openings in the dorsal surface of the oesophagus connecting to the external surface, through which water from the food can be squeezed, helping to concentrate it. Digestion occurs in the intestine, with food material being pulled through by cilia, rather than by muscular action.[13]

Acorn worms breathe by drawing in oxygenated water through their mouth. The water then flows out the animal's gills which are on its trunk. Thus, the acorn worm breathes about the same way as fish.

Circulatory system

Acorn worms have an open circulatory system, in which the blood flows through the tissues sinuses. A dorsal blood vessel in the mesentery above the gut delivers blood to a sinus in the proboscis that contains a muscular sac acting as a heart. Unlike the hearts of most other animals, however, this structure is a closed fluid-filled vesicle whose interior does not connect directly to the blood system. Nonetheless, it does regularly pulsate, helping to push blood through the surrounding sinuses.[13]

From the central sinus in the collar, blood flows to a complex series of sinuses and peritoneal folds in the proboscis. This set of structures is referred to as a glomerulus and may have an excretory function, since acorn worms otherwise have no defined excretory system. From the proboscis, blood flows into a single blood vessel running underneath the digestive tract, from which smaller sinuses supply blood to the trunk, and back into the dorsal vessel.[13]

The blood of acorn worms is colourless and acellular.[13]

Respiratory system

Acorn worms continually form new gill slits as they grow in size, with some older individuals having more than a hundred on each side. Each slit consists of a branchial chamber opening to the pharynx through a U-shaped cleft and to the exterior through a dorso-lateral pore (see diagram below). Cilia push water through the slits, maintaining a constant flow. The tissues surrounding the slits are well supplied with blood sinuses.[13]

Nervous system

A plexus of nerves lies underneath the skin, and is concentrated into both dorsal and ventral nerve cords. While the ventral cord runs only as far as the collar, the dorsal cord reaches into the proboscis, and is partially separated from the epidermis in that region. This part of the dorsal nerve cord is often hollow, and may well be homologous with the brain of vertebrates. In acorn worms, it seems to be primarily involved with coordinating muscular action of the body during burrowing and crawling.[13]

Acorn worms have no eyes, ears or other special sense organs, except for the ciliary organ in front of the mouth, which appears to be involved in filter feeding and perhaps taste (3). There are, however, numerous nerve endings throughout the skin.[13]

Similarities to chordates

Acorn worms are considered more highly specialised and advanced than other similarly shaped worm-like creatures. They have a circulatory system with a heart that also functions as a kidney. Acorn worms have gill-like structures that they use for breathing, similar to the gills of primitive fish. Therefore, acorn worms are sometimes said to be a link between classical invertebrates and vertebrates. Some also have a postanal tail which may be homologous to the post-anal tail of vertebrates. An interesting trait is that its three-section body plan is no longer present in the vertebrates, except for the anatomy of the frontal neural tube, later developed into a brain which is divided into three main parts. This means some of the original anatomy of the early chordate ancestors is still present even if it is not always visible.

One theory is that the three-part body originates from an early common ancestor of all the deuterostomes, and maybe even from a common bilateral ancestor of both the deuterostomes and protostomes. Studies have shown that the gene expression in the embryo share three of the same signaling centers that shape the brains of all vertebrates, but instead of taking part in the formation of their neural system,[15] they are controlling the development of the different body regions.[16]

Lifestyle

Acorn worms are rarely seen by humans because of their lifestyle. They live in U-shaped burrows on the sea-bed, from the shoreline down to a depth of 10,000 ft. (3,050 m). The worms lie there with the proboscis sticking out of one opening in the burrow. Acorn worms are generally slow burrowers.

To obtain food, many acorn worms swallow sand or mud that contains organic matter and microorganisms in the manner of earthworms (this is known as deposit feeding). At low tide, they stick out their rear ends at the surface and excrete coils of processed sediments (casts).

Another method that some acorn worms use to obtain food is to collect suspended particles of organic matter and microbes from the water. This is known as suspension feeding.[14]

Reproduction

Acorn worms are dioecious, having separate biological sexes, although at least some species are also capable of asexual reproduction. They have paired gonads, which lie close to the pharynx and release the gametes through a small pore near to the gill slits. The female lays a large number of eggs embedded in a gelatinous mass of mucus, which are then externally fertilized by the male before water currents break up the mass and disperse the individual eggs.[13]

AcornWormCycle
Acorn worm life cycle by M. Singh

In most species, the eggs hatch into planktonic larvae with elongated bodies covered in cilia. In some species, these develop directly into adults, but in others, there is a free-swimming intermediate stage referred to as a tornaria larva. These are very similar in appearance to the bipinnaria larvae of starfishes, with convoluted bands of cilia running around the body. Since the embryonic development of the blastula within the egg is also very similar to that of echinoderms, this suggests a close phylogenetic link between the two groups.[13]

After a number of days or weeks, a groove begins to form around the larval midsection, with the anterior portion eventually destined to become the proboscis, while the remainder forms the collar and trunk. The larvae eventually settle down and change into tiny adults to take on the burrowing lifestyle. A few species, such as Saccoglossus kowalevskii, lack even the planktonic larval stage, hatching directly as miniature adults.[13]

References

  1. ^ Konikoff, C; van der Land, J (2011). "Enteropneusta". WoRMS. World Register of Marine Species. Retrieved 2017-11-20.
  2. ^ Cameron, CB; Garey, JR; Swalla, BJ (2000). "Evolution of the chordate body plan: New insights from phylogenetic analyses of deuterostome phyla". Proceedings of the National Academy of Sciences of the United States of America. 97 (9): 4469–74. Bibcode:2000PNAS...97.4469C. doi:10.1073/pnas.97.9.4469. PMC 18258. PMID 10781046.
  3. ^ Biogeography and adaptations of torquaratorid acorn worms (Hemichordata: Enteropneusta) including two new species from the Canadian Arctic - Research Proposal - Papyrus - Université de Montréal
  4. ^ Hemichordate genomes and deuterostome origins | Nature
  5. ^ Smith, KL; Holland, ND; Ruhl, HA (July 2005). "Enteropneust production of spiral fecal trails on the deep-sea floor observed with time-lapse photography". Deep Sea Research Part I: Oceanographic Research Papers. 52 (7): 1228–1240. Bibcode:2005DSRII..52.1228S. doi:10.1016/j.dsr.2005.02.004.
  6. ^ Holland, ND; Clague, DA; Gordon, DP; Gebruk, A; Pawson, DL; Vecchione, M (2005). "'Lophenteropneust' hypothesis refuted by collection and photos of new deep-sea hemichordates". Nature. 434 (7031): 374–376. Bibcode:2005Natur.434..374H. doi:10.1038/nature03382. PMID 15772659.
  7. ^ Holland ND, Jones WJ, Elena J, Ruhl HA, Smith KL (2009) A new deep-sea species of epibenthic acorn worm (Hemichordata, Enteropneusta). Zoosystema 31: 333—346.
  8. ^ Osborn KL, Kuhnz LA, Priede IG, Urata M, Gebruk AV, and Holland ND (2012) Diversication of acorn worms (Hemichordata, Enteropneusta) revealed in the deep sea. Proc. Roy. Soc. Lond. B 279: 1646—1654.
  9. ^ Priede IG, Osborn KJ, Gebruk AV, Jones D, Shale D, Rogacheva A, Holland ND (2012) Observations on torquaratorid acorn worms (Hemichordata, Enteropneusta) from the North Atlantic with descriptions of a new genus and three new species. Invert. Biol. 131: 244-257.
  10. ^ The secret to an Oesia life: Prehistoric worm built tube-like 'houses' on sea floor
  11. ^ Florkin, Marcel (2014). Deuterostomians, Cyclostomes, and Fishes. Elsevier. p. 83. ISBN 9780323163347.
  12. ^ a b  One or more of the preceding sentences incorporates text from a publication now in the public domainWilley, Arthur (1911). "Balanoglossus". In Chisholm, Hugh (ed.). Encyclopædia Britannica. 3 (11th ed.). Cambridge University Press. pp. 237–239.
  13. ^ a b c d e f g h i j k l m n Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 1018–1026. ISBN 978-0-03-056747-6.
  14. ^ a b Cameron, C. (2002). "Particle retention and flow in the pharynx of the enteropneust worm Harrimania planktophilus: The filter-feeding pharynx may have evolved before the chordates". The Biological Bulletin. 202 (2): 192–200. doi:10.2307/1543655. JSTOR 1543655. PMID 11971814.
  15. ^ Secondary organizers of the early brain and the location of the meso-diencephalic dopaminergic precursor cells Retrieved March 10, 2014
  16. ^ Rob Mitchum (March 15, 2012). "The Secret Origin of the Vertebrate Brain". ScienceLife. Retrieved February 18, 2014.
Balanoglossus

Balanoglossus is an ocean-dwelling acorn worm (Enteropneusta) genus of great zoological interest because, being a Hemichordate, it is an "evolutionary link" between invertebrates and vertebrates. Balanoglossus is a deuterostome, and resembles the Ascidians or sea squirts, in that it possesses branchial openings, or "gill slits". It has notochord in the upper part of the body and has no nerve chord. It does have a stomochord, however, which is gut chord within the collar. Their heads may be as small as 2.5 mm (1/10 in) or as large as 5 mm (1/5 in).

Balanoglossus australiensis

Balanoglossus australiensis is a species of 20 centimetres (7.9 in) long acorn worm in Ptychoderidae family which can be found in Gulf of Carpentaria, New Zealand, Western Australian cities such as Hawkesbury and Manning as well as Solomon Archipelago and its sea. Their habitat consists of 8–10 inches (200–250 mm) deep sandy burrows where they feed on Ubius species.

CCDC92

CCDC92, or Limkain beta-2, is a protein which in humans is encoded by the CCDC92 gene. It is likely involved in DNA repair or reduction/oxidation reactions. The gene ubiquitously found in humans and is highly conserved across animals.The CCDC92 gene is located at cytogenic location 12q24.31 and is 36,576 bases long with nine exons which codes for a 331 amino-acid long protein.

Cornelius van der Horst

Cornelius Jan van der Horst (born 11 May 1889 in Nieuwer-Amstel, died Johannesburg 10 October 1951) was a Dutch biologist who worked mainly on marine biology and embryology in both the Netherlands and South Africa. As an undergraduate he studied botany and zoology at the University of Amsterdam where he was appointed assistant in the Botany Department under Professor Dr Hugo de Vries before moving on to assist Max Wilhelm Carl Weber at the University's Zoological Museum and in 1917 he became the principal assistant for general Zoology. In 1916 he published his thesis De motorische kernen en banen in de hersenen der visschen. Hare taxonomische waarde en neurobiotactische beteekenis ("The motor nuclei and orbits in the brain of the fish. Its taxonomic value and neurobiotactic meaning "). The research for this thesis was carried out at the Netherlands Central Institute for Brain Research under C. U. Ariëns Kappers. In 1925 Van der Horst was appointed Deputy Director of this Netherlands Central Institute for Brain Research and in 1928 he moved to South Africa where he took up a post as senior lecturer in zoology at the University of The Witwatersrand in Johannesburg. in 1932 he was promoted to professor in zoology at this University.Van der Horst's early research concentrated on the anatomy of the nervous system of fishes and he published papers on this topic, at the same time he grew interested in corals and published a monograph on the Fungiidae, Agariciidae and Eupsammiidae collected by the Siboga Expedition, as well as writing a paper on the Agariciidae collected by the Percy Sladen Expedition of the Linnean Society. In 1920 Van der Horst undertook a trip to Curaçao to conduct research into the marine fauna, he had studies so many coral skeletons that he wanted to examine the living organisms. He stayed at the old Quarantine Station on the island and studies the fauna using a box with a glass bottom but his studies were much facilitated when the Chief of Public Works lent him a diving suit. He amassed a large collection of specimens while in Curaçao and these specimens were studied by over twenty specialists and resulted in many papers. van der Horst wrote a travelogue detailing the sites where he collected his specimens and later he published a list of the corals with notes on their morphology. At the same time he was editing papers on the acorn worms or Enteropneusta, a group of animals about which he was to publish a series of publications. In his research on acrorn worms he demonstrated a thorough knowledge of the literature, as well as a clear understanding of the complex anatomy and morphology of this group, he soon becaome recognised as one of the leading authorities on the Enteropneusta. While in Curaçao among the specimens he collected was the type of a new species of goby which was subsequently named after him, Elacatinus horsti.Following his trip to Curaçao, van der Horst continued to research brain anatomy for a few months under Charles Judson Herrick at the University of Chicago. His continuing interest in this field was shown some years later when he went to Stockholm to collaborate with Nils Holmgren in an investigation into the anatomy of the brain of Neoceratodus. He also wrote several chapters in Heinrich Georg Bronn's Klassen und Ordnungen des Thier-Reichs, wissenschaftlich dargestellt in Wort und Bild (Classes and orders of the Animal Kingdom, scientifically represented in words and pictures") and contributed a chapter on spinal nerves to the "Handbuch der Vergleichenden Anatomie der Wirbeltiere ("Handbook of Comparative Anatomy of Vertebrates").In South Africa, van der Horst continued his research in the field of systematic zoology, publishing many article on acorn worms, corals and new and remarkable fish from South Africa, as well as some work on mammal systematics. At this time he was beginning to gather materials to conduct research into the embryology of mammals. Between 1940 and 1946 he published a series of articles with Joseph Gilman on embryology on the group of African mammals now known as Afrotheria, such as aardvark, golden moles and elephant shrews, their work being important in clarifying the systematics of these mammals. The visit to Curaçao had stimulated a lifelong interest in marine biology and when in South Africa he conducted expeditions to Inhaca with his students and gradually a small marine biological station was created there, which van der Horst helped create with the cooperation of Portuguese colonial authorities in Mozambique. He was instrumental in organising research into the fossil reptiles and mammals of South Africa; and connected the University of the Witwatersrand with the Bernard Price Institute for Palaeontological Research. He was honorary director of the Bernard Price Institute for Palaeontological Research.He was a member of the Royal Society of South Africa, a correspondent of the Royal Dutch Academy of Sciences, a foreign member of the Norwegian Academy of Science and Letters, a member of the Institute International d'Embryologie and a corresponding member of the Zoological Society of London. He was awarded a gold medal by the Swedish Academy of Sciences in 1950

awarded in commemoration of Carl Linnaeus. Other species named for van der Horst include the ribbon worm Micrura vanderhorsti, the upside down jellyfish Cassiopea vanderhorsti and the acorn worm Saccoglossus horsti.

Gulf of Mannar

The Gulf of Mannar ( mə-NAR) is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean. It lies between the west coast of Sri Lanka and the southeastern tip of India, in the Coromandel Coast region. The chain of low islands and reefs known as Ramsethu, also called Adam's Bridge, which includes Mannar Island, separates the Gulf of Mannar from Palk Bay, which lies to the north between Sri Lanka and India. The Malvathu Oya (Malvathu River) of Sri Lanka and the estuaries of Thamirabarani River and Vaipar River of South India drain into the Gulf. The dugong (sea cow) is found here.

Harrimania planktophilus

Harrimania planktophilus is a marine acorn worm in the family Harrimaniidae. It lives in a burrow in sediment on the sea floor. It is only known from western Canada and was first described by Cameron in 2002. The species name is from the Greek and translates as "lover of plankton".

Harrimaniidae

Harrimaniidae is a basal family of acorn worms. A taxonomic revision was undertaken in 2010, and a number of new genera and species found in the Eastern Pacific were described. There is some indication that Stereobalanus may be a separate basal acorn worm lineage, sister to all remaining acorn worms.

Hemichordate

Hemichordate is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species, Planctosphaera pelagica. The extinct class Graptolithina is closely related to the pterobranchs.Acorn worms are solitary worm-shaped organisms. They generally live in burrows (the earliest secreted tubes) and are deposit feeders, but some species are pharyngeal filter feeders, while the family Torquaratoridae are free living detritivores. Many are well known for their production and accumulation of various halogenated phenols and pyrroles. Pterobranchs are filter-feeders, mostly colonial, living in a collagenous tubular structure called a coenecium.

List of unusual biological names

The trouble with unusual names have not been lost on scientists when needing to explain genetic diseases to lay-people. This has particularly been noted in patients with a defect in the sonic hedgehog gene pathway and the disease formerly named CATCH22 for "cardiac anomaly, T-cell deficit, clefting and hypocalcaemia for chromosome 22q11.2 microdeletions". This name was abandoned due to the no-win connotations.In 1993, a researcher at the University of Cambridge was ordered to change the name of the gene he had discovered, VELCRO, because of copyright issues with Velcro. The gene was re-named to puckered. In 2005, Pokémon threatened to sue the discoverer of POKEMON because the name was attracting attention when its link to the development of cancer was published.

Meioglossus

Meioglossus psammophilus is a species of acorn worm in the family Harrimaniidae, the only known species of the genus Meigolossus. It inhabits the Western Caribbean and Bermuda. The name of the species derives from two Greek words; psammon and philos which in translation means friend of the sands in reference to adult stage of species' lifestyle. The length of the species is 0.6 millimetres (0.024 in).

Mesoglossus caraibicus

Mesoglossus caraibicus is a species of acorn worm in the family Harrimaniidae, which can be found on Bahamas, Greater Antilles, Southern Caribbean, and Gulf of Mexico.

Mesoglossus pygmaeus

Mesoglossus pygmaeus is a species of acorn worm in the family Harrimaniidae, which is found in Europe, precisely in British Isles.

MirGeneDB

MirGeneDB is a database of microRNA genes that have been validated and annotated as described in Fromm et al. 2015. The initial version contained 1'434 microRNA genes for human, mouse, chicken and zebrafish. Version 2.0 will contain more than 10'000 genes from 45 organisms representing nearly every metazoan group, and these microRNAs can be browsed, searched and downloaded. Planned release data for 2.0 is December 2019.

Eutheria (Placental mammals)

• Human (Homo sapiens)

• Rhesus monkey (Macaca mulatta)

• House mouse (Mus musculus)

• Norway rat (Rattus norvegicus)

• Guinea pig (Cavia porcellus)

• Rabbit (Oryctolagus cuniculus)

• Dog (Canis familiaris)

• Cow (Bos taurus)

• Nine-banded armadillo (Dasypus novemcinctus)

• Lesser hedgehog tenrec (Echinops telfairi)Aves (Birds)

• Chicken (Gallus gallus)

• Rock pigeon (Columba livia)Crocodylia (Alligators and Crocodiles)

• American alligator (Alligator mississippiensis)Testudines (Turtles)

• Western painted turtle (Chrysemys picta bellii)Squamata (Lizards and snakes)

• Green anole lizard (Anolis carolinensis)Anura (Frogs and toads)

• Tropical clawed frog (Xenopus tropicalis)Teleostei (Teleost fish)

• Zebrafish (Danio rerio)Cephalochordata

• Florida lancelet (Branchiostoma floridae)Hemichordata

• Acorn worm (Saccoglossus kowalevskii)

• Acorn worm 2 (Ptychodera flava)Echinodermata

• Purple sea urchin (Strongylocentrotus purpuratus)

• Bat starfish (Patiria miniata)Hexapoda

• Fruit fly (Drosophila melanogaster)

• Red flour beetle (Tribolium castaneum)Crustacea

• Common water flea (Daphnia pulex)Chelicerata

• Black-legged tick (Ixodes scapularis)Nematoda

• Roundworm (Caenorhabditis elegans)

• Large roundworm (Ascaris suum)Mollusca

• Owl limpet (Lottia gigantea)

• Pacific oyster (Crassostrea gigas)Annelida

• Polychaete worm (Capitella teleta)

• Common brandling worm (Eisenia fetida)

Ptychodera

Ptychodera is a genus of acorn worm.

Saccoglossus

Saccoglossus is a genus of acorn worm (Class Enteropneusta). It is the largest genus in this class, with 18 species.This genus is characterized especially by the concentric rings of muscle fibers in the proboscis. Many Saccoglossus can be found in coastal mud and sand habitat, often near bays. They dig tubes in the substrate, ejecting conical piles of castings in a spiral fashion.Acorn worms of this genus are known for the production and accumulation of various halogenated phenols and pyrroles.

Saccoglossus bromophenolosus

Saccoglossus bromophenolosus is a species of acorn worm (class Enteropneusta) occurring in the northwestern Atlantic Ocean and the northeastern Pacific Ocean. It grows to a length of about 20 cm (8 in) and lives in a burrow in soft sediment in the intertidal and subtidal zones. The scientific name refers to 2,4-dibromophenol, a secondary metabolite present in this worm.

Spartobranchus tenuis

Spartobranchus tenuis is an extinct species of acorn worms (Enteropneusta). It existed in the Middle Cambrian (505 million years ago). Petrified mark animals were found in British Columbia, Canada in the formation Burgess Shale. It is similar to the modern representatives of the family Harrimaniidae, distinguished by branching fiber tubes. It is a believed predecessor of Pterobranchia, but this species is intermediate between these two classes. Studies show that these tubes were lost in the line leading to modern acorn worm, but remained in the extinct graptolites and saving still perystozyabernyh.

Yoda purpurata

Yoda purpurata is a species of acorn worm from the North Atlantic ocean, and the sole species of the genus Yoda. Ranging from 12 to 19 cm (4.7 to 7.5 in) in length, it was named after the fictional character Yoda from the Star Wars franchise. It is the only known hermaphroditic member within the phylum.

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