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34.1 Ctenophores: The Earliest Animals
A sticky substance is released from the two long tentacles of most comb jellies.
Small Prey include ceans called copepods and small fishes.
In the 1980s, comb was introduced into the Black and Caspian seas.
The free-swimming larva is very similar to the adult.
It was particularly evident at night.
Sometimes they wash up on the shore and make the sand or mud glow.
Ctenophores have both muscle and nerve cells that are close rel organized as a diffuse net at an elementary brain.
The ctenophore nervous system has different types of corals and different types of ters.
The presence of muscle cells from recent studies has changed the view that ctenophores share a three-germ-layer embryonic farther apart on the animal evolutionary tree.
There are genes involved in specifying bilaterian mesoderm.
The ctenophores are propelled by coordinated beating of the cilia.
Bilaterian neuron-specific genes are absent or not expressed in ctenophores.
The findings argue against a linear march of evolutionary forms from simpler animals to more complex ones.
The studies suggest that ctenophores were the earliest animals to have a simple nervous system.
The ctenophores have a different way of forming the mesoderm than the bilaterians.
Ctenophores are commonly referred to as sponges.
The eight rows of cilia on the sponges' surfaces look like combs.
The sponges are anchored in place.
Small particulate matter and tiny plankton are eaten by choanocytes in the pro cess.
A common sponge found on Caribbean reefs is the stovepipe sponge.
There are sponges with a vaselike shape.
sponges are multicellular animals, having various cell types but as a mode of feeding, and using a cross section to reveal this.
Skeletal fibers formed by amoebocytes may explain why sponges are rare.
The sponge has its body.
Spongin skeletons are still commercially harvested and sold as bath examples.
Many species produce toxic defensive chemicals by having needle-like silica spicules that form elabo, which are being tested as possible anticancer and anti- inflammatory rate lattice-like skeletons.
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