trichocephalus) 129 brachiopods and 185 hemichordates
One of the big punchlines from my graduate work, was molecular evidence that enteropneusts and pterobranchs are closely related," said Cameron, a specialist on the taxonomy, evolution and biogeography of hemichordates
But Shu and others contested that interpretation, arguing in the April 4 NATURE that Yunnanozoon was a hemichordate
, a separate phylum that includes the modern acorn worm.
Biomineral ultrastructure, elemental constitution and genomic analysis of biomineralization-related proteins in hemichordates
The creature belongs to a group called pterobranch hemichordates
which are related to starfish and sea urchins but also show some characteristics that offer clues to the evolution of the earliest vertebrates.
In preliminary studies, Shu Degan of Xian Northwest University places Yunnanozoon in another phylum, the hemichordates
, which includes the modern acorn worms.
, a small marine phylum integral to hypotheses on deuterostome and chordate evolution, occur throughout the world's oceans.
Professor Max Telford, from the UCL Department of Genetics, Evolution and Environment, and joint leader of the research said: "Because the simple Xenacoelomorpha are descended from the same ancestor that gave rise to complex groups such as vertebrates, echinoderms and hemichordates
, these simple worms must have lost a lot of the complexity that they originally possessed.
proportion of taxa with hard parts that are likely to fossilize) is high in 14 % (bivalve and gastropod molluscs), intermediate in 26 % (brachiopods, echinoderms, arthropods) and low in 60 % that have only soft parts (polychaetes, turbellarians, oligochaetes, hemichordates
and nemerteans) (see Vargas 1987, 1988 b).
A 95% majority rule consensus tree for hemichordates
(40 million generations) was constructed from concatenated, but unlinked nucleotide sequences (with no regions excluded) in MrBayes 3.
Deuterostomia is a super phylum that encompasses hemichordates
(Enteropneusta), echinoderms (sea urchins), and chordates (vertebrates); along with the phylum protostomia, it represents all animals having bilateral symmetry at least early in development (Fig.
It has been considered to correspond, at least in part, to the protocoel of hemichordates
(MacBride, 1909), the original foregut of chordates (van Wijhe, 1913), the pre-premandibular head cavities of craniates (Neal, 1915), or the premandibular head cavities plus part of the adeno-hypophysis of craniates (Goodrich, 1917).