| Balanoglossus | |
|---|---|
| |
| Unidentified specimen from Réunion | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Hemichordata |
| Class: | Enteropneusta |
| Order: | Enteropneusta |
| Family: | Ptychoderidae |
| Genus: | Balanoglossus Delle Chiaje, 1829 |
| Species | |
|
See text. | |
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, and resembles the sea squirts (Ascidiacea) in that it possesses branchial openings, or "gill slits". 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).
The discovery of gill-slits in this animal by Alexander Kovalevsky (1865) led to the creation of the class Enteropneusta by Carl Gegenbaur (1870).
William Bateson (1885) originally included them in phylum Chordata.[1] Hyman (1959), however, placed them near Echinodermata and gave Hemichordata a status of an independent phylum.
Balanoglossus is a tuberculos[spelling?] (burrowing) and exclusively marine animal. It is found in shallow waters between tide marks along the coast of warm and temperate oceans.
The World Register of Marine Species lists the following species:[2]
