Balanoglossus is a genus of ocean-dwelling acorn worms. It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. Balanoglossus specimens are deuterostomes, and resemble the chordates 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 discovered Balanoglossus in 1825 on Mashail Island, and described it as a worm-like holothurian. The discovery of gill slits in these animals by Alexander Kovalevsky (1865) led to the creation of the class Enteropneusta by Carl Gegenbaur (1870).
Classification
William Bateson (1885) originally included them in phylum Chordata. Hyman (1959), however, placed them near Echinodermata and gave Hemichordata a status of an independent phylum.
Habitat
alt=1. Ptychodera clavigera, von der dorsalen Seite. 1 / l . Nach dem Leben. 2. Ptychodera minuta q 1, von der ventralen Seite. 2 /i- Nach dem Leben. 3. desgl. Q, von der dorsalen Seite. 2 /j. Nach dem Leben. 4. Ptyclwdera erythraea, von der dorsalen Seite. Vi- Nach den vorhandnen Bruchstücken des einzigen, in Spiritus conservirten Exemplars. 5. ScMzocardium brasiliense, von der Seite. Nach dem Leben. 6. Glandiceps talaboti. Vorderkörper, von der dorsalen Seite, '/i* Nach dem Leben. 7. Glandiceps haeksi, erwachsen, Vorderkörper von der ventralen Seite. Vi- Nach dem mir vor- liegenden Spiritus -Exemplar. 8. Dasselbe Exemplar von der dorsalen Seite. 9. Junges Individuum derselben Art. 2 /i- Nach einem Spiritus -Exemplar. 10. Balanoglossus Jcoicalevskii. 4 /i- Nach dem Leben. 11. Balanioglossus hupfferi. i / i . Nach dem Leben. Die Originale zu Fig. 2, 3, 4, 7, 8 sind von Herrn O. Peters in Göttingen, zu Fig. 5 von Herrn Prof. E. Selenka in Erlangen, zu Fig. 6 von Herrn Merculiako in Neapel, zu Fig. 10 von Herrn Prof. Charles S. Minot in Boston, zu Fig. 1, 9 und 11 von mir angefertigt.|thumb|Acorn worms. Specimens 10 and 11 are Balanoglossus.
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 lists the following species:
- Balanoglossus apertus <small>Spengel, 1893</small>
- Balanoglossus aurantiaca <small>Girard, 1853</small>
- Balanoglossus australiensis <small>Hill, 1894</small>
- Balanoglossus biminiensis <small>Willey, 1899</small>
- Balanoglossus borealis <small>Willey, 1899</small>
- Balanoglossus capensis <small>Gilchrist, 1908</small>
- Balanoglossus carnosus <small>Willey, 1899</small>
- Balanoglossus clavigerus <small>Delle Chiaje, 1829</small>
- Balanoglossus gigas <small>Müller in Spengel, 1893</small>
- Balanoglossus hydrocephalus <small>van der Horst, 1940</small>
- Balanoglossus jamaicensis <small>Willey, 1899</small>
- Balanoglossus misakiensis <small>Kuwano, 1902</small>
- Balanoglossus natalensis <small>Gilchrist, 1908</small>
- Balanoglossus numeensis <small>Maser, 1913</small>
- Balanoglossus occidentalis <small>Ritter, 1902</small>
- Balanoglossus parvulus <small>Punnett, 1903</small>
- Balanoglossus proterogonius <small>Belichov, 1928</small>
- Balanoglossus robinii <small>Giard, 1882</small>
- Balanoglossus salmoneus <small>Belichov, 1928</small>
- Balanoglossus simodensis <small>Miyamoto & Saito, 2007</small>
- Balanoglossus stephensoni <small>van der Horst, 1937</small>
- Balanoglossus studiosorum <small>van der Horst, 1940</small>