''Balanoglossus'' is a genus of ocean-dwelling

acorn worm The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in th ...

s (Enteropneusta). It has zoological importance because, being

hemichordate Hemichordata is a phylum which consists of triploblastic, enterocoelomate, and bilaterally symmetrical marine deuterostome animals, generally considered the sister group of the echinoderms. They appear in the Lower or Middle Cambrian and includ ...

s, they are an "evolutionary link" between

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s and

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...

s. ''Balanoglossus'' is a deuterostome, and resembles the sea squirts (

Ascidiacea Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" ...

) in that it possesses branchial openings, or "

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s". It has a notochord in the upper part of the body and has no nerve chord. It does have a stomochord, however, which is a gut chord within the collar. Their heads may be as small as per 2.5 mm (1/10 in) or as large as 5 mm (1/5 in).

Discovery

The discovery of gill-slits in this animal by

Alexander Kovalevsky Alexander Onufrievich Kovalevsky (russian: Алекса́ндр Ону́фриевич Ковале́вский, 7 November 1840 in Vārkava parish, Vorkovo, Dvinsky Uyezd, Vitebsk Governorate, Russian Empire – 1901, St. Petersburg, Russian Empi ...

(1865) led to the creation of the class

Enteropneusta The acorn worms or Enteropneusta are a hemichordate class of invertebrates consisting of one order of the same name. The closest non-hemichordate relatives of the Enteropneusta are the echinoderms. There are 111 known species of acorn worm in the ...

Karl Gegenbaur Karl Gegenbaur (21 August 1826 – 14 June 1903)"Karl Gegenbaur – Encyclopædia Britannica" (biography), ''Encyclopædia Britannica'', 2006, Britannica.coBritannica-KarlG was a German anatomist and professor who demonstrated that the field of c ...

(1870).

Classification

William Bateson William Bateson (8 August 1861 – 8 February 1926) was an English biologist who was the first person to use the term genetics to describe the study of heredity, and the chief populariser of the ideas of Gregor Mendel following their rediscove ...

(1885) originally included them in phylum Chordata. Hyman (1959), however, placed them near

Echinodermata An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

and gave Hemichordata a status of an independent phylum.

Habitat

Balanoglossus is a tuberculos (burrowing) and exclusively marine animal. It is found in shallow waters between tide marks along the coast of warm and temperate oceans.

Species

The

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained by scientific specialis ...

lists the following

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

:Balanoglossus - delle Chiaje, 1829
World Register of Marine Species. Retrieved 2022-12-14. * ''

Balanoglossus apertus ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Spengel, 1893 * ''

Balanoglossus aurantiaca ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Girard, 1853 * '' Balanoglossus australiensis'' Hill, 1894 * ''

Balanoglossus biminiensis ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Willey, 1899 * '' Balanoglossus borealis'' Willey, 1899 * '' Balanoglossus capensis'' Gilchrist, 1908 * ''

Balanoglossus carnosus ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Willey, 1899 * '' Balanoglossus clavigerus'' Delle Chiaje, 1829 * '' Balanoglossus gigas'' Müller in Spengel, 1893 * '' Balanoglossus hydrocephalus'' van der Horst, 1940 * ''

Balanoglossus jamaicensis ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome ...

'' Willey, 1899 * '' Balanoglossus misakiensis'' Kuwano, 1902 * '' Balanoglossus natalensis'' Gilchrist, 1908 * '' Balanoglossus numeensis'' Maser, 1913 * ''

Balanoglossus occidentalis ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Ritter, 1902 * '' Balanoglossus parvulus'' Punnett, 1903 * ''

Balanoglossus proterogonius ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Belichov, 1928 * ''

Balanoglossus robinii ''Balanoglossus'' is a genus of ocean-dwelling acorn worms (Enteropneusta). It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, ...

'' Giard, 1882 * '' Balanoglossus salmoneus'' Belichov, 1928 * '' Balanoglossus simodensis'' Miyamoto & Saito, 2007 * '' Balanoglossus stephensoni'' van der Horst, 1937 * '' Balanoglossus studiosorum'' van der Horst, 1940

References

{{Taxonbar, from=Q1768028 Enteropneusta Hemichordate genera