1B) and fecal mounds of hemichordates
. Snails like the scavenger Nassarius luteostoma and the predator Natica unifasciata crawl on the sediment surface year around, while the sand dollar Encope stokessi is more frequent during the dry seasons.
"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.
Because echinoderms and hemichordates
are sister groups, it is probable that certain aspects of the regeneration process are shared between the two groups.
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.
The deuterostome superphylum comprises the chordates, which include all vertebrates, hemichordates
(acorn worms), and echinoderms (Satoh et al., 2014); echinoderms themselves are comprised of sea urchins, sea stars, brittle stars, sea cucumbers, sand dollars, and crinoids.
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).
(Saccoglossus kowalevskii), echinoderms (Strongylocentrotus purpuratus), and some vertebrates (see Table 2 for GenBank sequence accession numbers for the data in Fig.
Acorn worms (Enteropneusta), a solitary class of hemichordates
, are marine vermiform invertebrates that generally live concealed in burrows (Hyman, 1959).
, a small marine phylum integral to hypotheses on deuterostome and chordate evolution, occur throughout the world's oceans.