Is cnidaria a phylum?

Cnidaria ( / naɪˈdɛəriə /) is a phylum under Kingdom Animalia containing over 11,000 species of animals found exclusively in aquatic (freshwater and marine) environments: they are predominantly marine. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey.

How old is Cnidaria?

Cnidaria. However, molecular clock analysis of mitochondrial genes suggests a much older age for the crown group of cnidarians, estimated around 741 million years ago, almost 200 million years before the Cambrian period as well as any fossils.

Are cnidarians triploblastic?

However, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer. As a result, some recent text books classify ctenophores as triploblastic, and it has been suggested that cnidarians evolved from triploblastic ancestors.

Why are cnidarians limited to shallow waters?

Many cnidarians are limited to shallow waters because they depend on endosymbiotic algae for much of their nutrients. The life cycles of most have polyp stages, which are limited to locations that offer stable substrates. Nevertheless, major cnidarian groups contain species that have escaped these limitations.

What are the 4 types of cnidarians?

Modern cnidarians are generally classified into four main classes: sessile Anthozoa (sea anemones, corals, sea pens); swimming Scyphozoa (jellyfish) and Cubozoa (box jellies); and Hydrozoa, a diverse group that includes all the freshwater cnidarians as well as

What is the prey of cnidarians?

Prey of cnidarians ranges from plankton to animals several times larger than themselves. Some cnidarians are parasites, mainly on jellyfish but a few are major pests of fish.

What type of symmetry do cnidarians have?

Cnidarians exhibit primary radial symmetry. In the Hydrozoa and Scyphozoa all diameters are apolar (i.e. have like ends). Furthermore, any two diameters at right angles to each other are also alike, dividing the animal into