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

acorn worms 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 ...

. It has zoological importance because, being

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

s, they are an "evolutionary link" between

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s and

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s. ''Balanoglossus'' specimens are

deuterostomes Deuterostomes (from Greek: ) are bilaterian animals of the superphylum Deuterostomia (), typically characterized by their anus forming before the mouth during embryonic development. Deuterostomia comprises three phyla: Chordata, Echinodermata, ...

, and resemble the

chordates A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...

in that they possess branchial openings. Their heads are between 2.5 mm (1/10 in) and 5 mm (1/5 in) wide.

Discovery

Johann Friedrich von Eschscholtz Johann Friedrich Gustav von Eschscholtz (1 November 1793 – 7 May 1831)Sterling (1997) was a Baltic German physician, naturalist, and entomologist. He was one of the earliest scientific explorers of the Pacific region, making significant collec ...

discovered ''Balanoglossus'' in 1825 on Mashail Island, and described it as a worm-like

holothurian Sea cucumbers are echinoderms from the class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number being in the Asia� ...

. The discovery of gill slits in these animals by

Alexander Kovalevsky Alexander Onufrievich Kovalevsky (; 7 November 1840 – 1901) was a Russian embryologist, who studied medicine at the University of Heidelberg and became professor at the University of St Petersburg. He was the brother of the paleontologist V ...

(1865) led to the creation of the class Enteropneusta by

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

(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 rediscover ...

(1885) originally included them in

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Chordata A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (Apomorphy and synapomorphy, synapomorphies) th ...

. Hyman (1959), however, placed them near

Echinodermata An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, ...

and gave

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

a status of an independent phylum.

Habitat

''Balanoglossus'' are burrowing, exclusively marine animals. They are 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 catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

lists the following

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

:Balanoglossus - delle Chiaje, 1829
World Register of Marine Species. Retrieved 2022-12-14. * ''Balanoglossus apertus'' Spengel, 1893 * ''Balanoglossus aurantiaca'' Girard, 1853 * ''

Balanoglossus australiensis ''Balanoglossus australiensis'' is a species of long acorn worm in Ptychoderidae family which can be found in Gulf of Carpentaria, New Zealand, Australian cities such as Hawkesbury and Manning as well as Solomon Archipelago and its sea ...

'' Hill, 1894 * ''Balanoglossus biminiensis'' Willey, 1899 * ''Balanoglossus borealis'' Willey, 1899 * ''Balanoglossus capensis'' Gilchrist, 1908 * ''Balanoglossus carnosus'' Willey, 1899 * ''Balanoglossus clavigerus'' Delle Chiaje, 1829 * ''

Balanoglossus gigas ''Balanoglossus gigas'' is a species of large free-living enteropneust (acorn worm) found in the Atlantic Ocean. It is the largest acorn worm currently known, and has a strong iodoform-like odour. It is bioluminescent. Description Size ''B ...

'' Müller in Spengel, 1893 * ''Balanoglossus hydrocephalus'' van der Horst, 1940 * ''Balanoglossus jamaicensis'' Willey, 1899 * ''Balanoglossus misakiensis'' Kuwano, 1902 * ''Balanoglossus natalensis'' Gilchrist, 1908 * ''Balanoglossus numeensis'' Maser, 1913 * ''Balanoglossus occidentalis'' Ritter, 1902 * ''Balanoglossus parvulus'' Punnett, 1903 * ''Balanoglossus proterogonius'' Belichov, 1928 * ''Balanoglossus robinii'' 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