Balanoglossus
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 and 5 mm 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 led to the creation of the class Enteropneusta by Carl Gegenbaur.
Classification
William Bateson originally included them in phylum Chordata. Hyman, however, placed them near Echinodermata and gave Hemichordata 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 lists the following species:Balanoglossus apertus Spengel, 1893Balanoglossus aurantiaca Girard, 1853Balanoglossus australiensis Hill, 1894Balanoglossus biminiensis Willey, 1899Balanoglossus borealis Willey, 1899Balanoglossus capensis Gilchrist, 1908Balanoglossus carnosus Willey, 1899Balanoglossus clavigerus Delle Chiaje, 1829Balanoglossus gigas Müller in Spengel, 1893Balanoglossus hydrocephalus van der Horst, 1940Balanoglossus jamaicensis Willey, 1899Balanoglossus misakiensis Kuwano, 1902Balanoglossus natalensis Gilchrist, 1908Balanoglossus numeensis Maser, 1913Balanoglossus occidentalis Ritter, 1902Balanoglossus parvulus Punnett, 1903Balanoglossus proterogonius Belichov, 1928Balanoglossus robinii Giard, 1882Balanoglossus salmoneus Belichov, 1928Balanoglossus simodensis Miyamoto & Saito, 2007Balanoglossus stephensoni van der Horst, 1937Balanoglossus studiosorum van der Horst, 1940