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Do cnidarians have no symmetry?
Body Symmetry of Cnidarians Cnidarians exhibit either the polyp or medusa body plan. The polyp body plan is cylindrical with one end attached to a surface and the other end containing a mouth surrounded by tentacles. Even though cnidarians vary a great deal, they all have radial symmetry as a common characteristic.
What do all cnidarians have in common?
All Cnidaria are aquatic, mostly marine, organisms. They all have tentacles with stinging cells called nematocysts that they use to capture food. Cnidarians only have two body layers, the ectoderm and endoderm, separated by a jelly-like layer called the mesoglea. Most Cnidarians have radial symmetry.
What distinguishes cnidarians from other animals?
Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are usually used mainly to capture prey. In some species, cnidocytes can also be used as anchors.
What animal does not have a brain?
There is one organism that has no brain or nervous tissue of any kind: the sponge. Sponges are simple animals, surviving on the sea floor by taking nutrients into their porous bodies.
Is a Cnidaria symmetrical?
Cnidarians are radially symmetrical (i.e., similar parts are arranged symmetrically around a central axis). They lack cephalization (concentration of sensory organs in a head), their bodies have two cell layers rather than the three of so-called higher animals, and the saclike coelenteron has one opening (the mouth).
Are there any cnidarians that have simple eyes?
Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually, with many species having complex life cycles of asexual polyp stages and sexual medusae.
How are cnidarians different from all other animals?
Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are usually used mainly to capture prey. In some species, cnidocytes can also be used as anchors.
What was the last common ancestor of cnidarians?
Our ancestral state reconstruction strongly suggests that the last common cnidarian ancestor ( Figure 1 A), as well as key ancestors in major medusozoan classes (Staurozoa, Scyphozoa, Cubozoa, and Hydrozoa), lacked eyes ( Figure 1 B).
Where are nerve cells located in the Cnidaria?
Main cell layers. These appear between or sometimes on top of the muscle cells. Nerve cells. Sensory cells appear between or sometimes on top of the muscle cells, and communicate via synapses (gaps across which chemical signals flow) with motor nerve cells, which lie mostly between the bases of the muscle cells.