What are cnidarians?
Cnidarians are a diverse group of invertebrates that come in many shapes and sizes but there are some basic features of their anatomy that most share in common. 01. of 10.
What are the two forms of a cnidarian?
Cnidarians take on two basic forms, a medusa and a polyp. The medusa form is a free-swimming structure which consists of an umbrella-shaped body (called a bell), a fringe of tentacles that hang from the edge of the bell, a mouth opening located on the underside of the bell, and a gastrovascular cavity.
How do tentacles work?
They use their tentacles to draw the food into their mouth and gastrovascular cavity. Once in the gastrovascular cavity, enzymes secreted from the gastrodermis break down the food. Small hair-like flagella that line the gastrodermis beat, mixing enzymes and food until the meal has been fully digested.
What are the different types of corals?
Corals belong to a group of cnidarians known as the Anthozoa. There are many types of coral and it should be noted that the term coral does not correspond to a single taxonomic class. Some groups of corals include: 1 Alcyonacea (soft corals) 2 Antipatharia (black corals and thorny corals) 3 Scleractinia (stony corals)
What is the internal sac of a cnidaria?
Purestock / Getty Images. Cnidarias have an internal sac for digestion which is called the gastrovascular cavity. The gastrovascular cavity has only one opening, a mouth, through which the animal takes in food and releases waste. Tentacles radiate outward from the rim of the mouth.
How many arms does a jellyfish have?
For example, many jellyfish have four oral arms that extend below their body and their body structure can therefore be divided into four equal parts. This type of radial symmetry is referred to as tetramerism. Additionally, two groups of cnidarians, corals and sea anemones, exhibit six- or eight-fold symmetry.
What is the outer layer of a cnidarian?
The body wall of a cnidarian consists of three layers, an outer layer known as the epidermis, a middle layer called the mesoglea, and an inner layer referred to as the gastrodermis. The epidermis contains a collection of different types of cells. These include epitheliomuscular cells which contract and enable movement, ...
What are the two body types of cnidarians?
They are the most primitive of animals whose cells are organized into distinct tissues, but they lack organs. Cnidarians have two body forms— polyp and medusa —which often occur within the life cycle of a single cnidarian. Chrysaora. Sea nettle ( Chrysaora fuscescens ). © Bobby Deal/RealDealPhoto/Shutterstock.com.
What is a cnidarian?
Cnidarian, also called coelenterate, any member of the phylum Cnidaria (Coelenterata), a group made up of more than 9,000 living species. Mostly marine animals, the cnidarians include the corals, hydras, jellyfish, Portuguese men-of-war, sea anemones, sea pens, sea whips, and sea fans. A sea anemone from the genus Tealia attached to a rock.
How big are cnidarian polyps?
Many cnidarian polyps are individually no more than a millimetre or so across. Polyps of most hydroids, hydrocorals, and soft and hard corals, however, proliferate asexually into colonies, which can attain much greater size and longevity than their component polyps. Certain tropical sea anemones (class Anthozoa) may be a metre in diameter, and some temperate ones are nearly that tall. Anthozoans are long-lived, both individually and as colonies; some sea anemones are centuries old. All medusae and sea anemones occur only as solitary individuals. Scyphomedusae can weigh more than a ton, whereas hydromedusae are, at most, a few centimetres across. Tentacles of medusae, however, may be numerous and extensible, which allows the animals to influence a considerably greater range than their body size might suggest. Large populations of hydroids can build up on docks, boats, and rocks. Similarly, some medusae attain remarkable densities—up to thousands per litre of water—but only for relatively brief periods.
Which is larger, a medusa or a polyp?
One body form may be more conspicuous than the other. For example, scyphozoans are commonly known as true jellyfishes, for the medusa form is larger and better known than the polyp form. In hydrozoans, the polyp phase is more conspicuous than the medusa phase in groups such as hydroids and hydrocorals. Hydromedusae are smaller and more delicate than scyphomedusae or cubomedusae; they may be completely absent from the life cycle of some hydrozoan species. Some other species produce medusa e, but the medusa e never separate themselves from the polyps. Cubozoans have medusae commonly known as box jellyfish, from their shape. Some of these are responsible for human fatalities, mostly in tropical Australia and Southeast Asia, and include the so-called sea wasps. The polyp is tiny and inconspicuous.
What is the shape of a jellyfish?
The body of a medusa, commonly called a jellyfish, usually has the shape of a bell or an umbrella, with tentacles hanging downward at the margin. The tubelike manubrium hangs from the centre of the bell, connecting the mouth at the lower end of the manubrium to the coelenteron within the bell.
Which is more conspicuous, a medusa or a scyphozoan?
One body form may be more conspicuous than the other. For example, scyphozoans are commonly known as true jellyfishes, for the medusa form is larger and better known than the polyp form. In hydrozoans, the polyp phase is more conspicuous than the medusa phase in groups such as hydroids and hydrocorals.
What is a coelenterate?
As first defined, coelenterates included not only the animals now designated cnidarians but also sponges (phylum Porifera) and comb jellies (phylum Ctenophora). In contemporary usage, “coelenterate” generally refers only to cnidarians, but the latter term is used in order to avoid ambiguity.
Which cnidarians have a small polyp stage?
Cnidarians that have a small polyp stage, but the dominant stage is free-swimming medusa. They include jellies.
What is the cnidocyte?
In a cnidocyte of a cnidarian, a specialized capsule-like organelle containing a coiled thread that when discharged can penetrate the body wall of the prey.
Which organisms are only polyps?
Cnidaria that occur only as polyps, including coral and sea anemones.
