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Australia: The Land Where Time Began |
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Cambrian Explosion - Chaetognatha The phylum Chaetognatha, small-bodied predators
that are largely pelagic, is likely to be represented by hook-shaped
spines in functional sets closely resembling grasping apparatuses of
chaetognaths in the Cambrian (Szaniawski, 1982) as well as body fossils
from the Chengjiang Fauna (J.Y. Chen & Huang, 2002) and the
Burgess
Shale (Szaniawski, 2005). Being neither spiralian nor lophophorate, the
Chaetognatha are suggested by molecular evidence to be protostomes
allied to Lophotrochozoa, and are possibly basal to those 2 groups
(Matus, Copley et al., 2006).
The clade, including Chaetognatha may include the LCA of extant
lophotrochozoans, if the topology is correct. About 20 % of extant
species are benthic and have been studied (Casenove, Goto & Vannier,
2011) for the functional and morphological differences between benthic
and pelagic forms. It is suggested by their analysis that species from
the Cambrian had a pelagic lifestyle. Chaetognaths have radial cleavage
and are literally deuterostomes; therefore it may be that these features
were inherited by the lophophorates, though in the branch leading to
Spiralia it was replaced by spiral cleavage and protostomy.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |