Balanoglossus

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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. It has zoological importance because, being hemichordates, they are an "evolutionary link" between invertebrates and vertebrates. Balanoglossus specimens are deuterostomes, and resemble the sea squirts in that they possess branchial openings, or "gill slits".^[1] They have notochords and stomochords but no dorsal nerve cord.

Their heads are between 2.5 mm (1/10 in) and 5 mm (1/5 in) wide.