Cnidarians are invertebrates, mainly living in the sea that has a single space inside them where food is digested. A mouth leads from the outside to the space, which is called the coelenteron. Often the mouth is surrounded by tentacles, which help to catch food and pass it into the coelenteron. Corals, sea anemones and jellyfish are all cnidarians. Both corals and sea anemones can look like plants at first sight.
Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a vertebral column, and some have evolved a shell or a hard exoskeleton. As on land and in the air, marine invertebrates have a large variety of body plans, and have been categorised into over phyla. They make up most of the macroscopic life in the oceans.
The earliest animals were marine invertebrates, that is, vertebrates came later. Animals are multicellular eukaryotes, and are distinguished from plants, algae, and fungi by lacking cell walls. Marine invertebrates are animals that inhabit a marine environment apart from the vertebrate members of the chordate phylum; invertebrates lack a vertebral column. Some have evolved a shell or a hard exoskeleton.
Picture Credit : Google
