NW Marine Life


Cnidarians: Lifestyle And Facts

There are over 9000 species of Cnidaria. They can mostly be found in the sea. They are invertebrates you don’t see everywhere. In fact, some of the species of this animal are so rare that you may never have seen them anywhere. A cnidarian is a member of the Cnidaria phylum.

There are many species that fall within this category including sea whips, jellyfish, sea pens. Most of the Cnidarians you’ll see all belong to the same origin. As such, they have a simple structure and they share similarity in features. Whether you’re a scientist or a layman, the features of this animal keep fascinating everyone.

For many tropical areas you’ll find, the skeletons of these animals are what you’ll find atop the areas. Their skeletons have created a structure for many tropical areas. This includes the great reef, which is located over 2000 kms along Australia’s Northern coast.

Features And Structure

These animals are symmetrical. Also, they do not have a concentration of sense organs. This is unlike the regular structure where an animal has the sensory organs all in the head. This is not the case with Cnidarians, as they lack such a structure.

They also have layers of two cells, which is predominantly how their structure is formed. Among the animals with two layer cells, these animals are the most primitive of all. Within their single life, there are two body forms, which they go through. These are medusa and polyp.

The medusa body is one which is often referred to as jellyfish. It mostly looks like an umbrella or a bell, and the tentacles hang down. Most medusa animals swim very slowly. On the flipside, a polyp would swim faster because the surrounding tentacles and the mouth are faced upwards, which account for why they may move at a fast pace.

Cnidarians And Humans

Most Cnidarians can affect human beings. While these animals are not exactly harmful, they can pose health risks in certain instances. For one, the Portuguese man-of-war can be injurious to human health.

Also, there are other species that are not palatable with human health. These species might become deadly in cases where they are too much or there has been an overdose. The species that are directly harmful to humans include the boxy jellyfish or the cubomedusae.

Cnidarian species can sexually reproduce at one particular phase all through their life cycle. This phase is often the medusae phase. It is also possible that polyps might remain joined with each other all through their cycle. In that case, the polyps will be using a coelenteron, which facilitates the redistribution of food when there’s one.


The preferred habitat for most polyps will be solid substrata to appropriately attach. There are some that will dig deep into soft sediment and leave only their tentacles out. These polyps are several in shallow waters.

A unique thing about Cnidarians is that there is restriction against the extent and area which predators can prey on. This keeps the fish safe. It also offers Cnidarians the opportunity to prey on competitors in order to secure space for expansion and dominance.