A marine invertebrate of the phylum Hemichordata; an acorn worm.
- The molecular phylogeny does agree in one respect with the morphological one in that there are close similarities between the larvae of hemichordates (acorn worms and pterobranchs) and some echinoderms.
- Unfortunately, a change in the genetic code of the mitochondrial genome in both enteropneusts and echinoderms strongly rejects chordate affinities of the hemichordates.
- Size comparisons between living and extinct hemichordate zooids are not conclusive evidence, however, as it is easy to imagine a small, hypothetical, zooid that possessed multiple tentaculated arms.
Relating to or denoting hemichordates.
- Evidence for the hemichordate affinity of the extinct graptolites has been steadily amassing.
- The hemichordate sequences always contained considerable support for both hypotheses.
- They lack two others, the notochord and post-anal tail, hence the name hemichordate.
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