Cnideria (Stinging Cells)

Family: Cnideria
This family is comprised of jellyfish, coral, sea pens, sea anemones, and diverse group of freshwater cniderians. These organisms are grouped together because they have specialized cells that they used mainly for capturing prey. All of them have either tentacles or thorns that contain stinging cells to paralyze their prey, which can include fish, crustaceans, or other soft-bodied organisms. Their body structure also affects how they kill prey. Jellyfish have a medusoid shape, which is a jelly-like umbrella and stinging tentacles emerging from it. Anemones have a polypoid shape, being immobile but stings unsuspecting prey with their tentacles or thorns.

True Jellyfish (Scyphozoa)
These organisms are soft-bodied aquatic creatures with a gelatinous umbrella-shaped bell and trailing tentacles. Jellyfish mainly like to digest plankton, crustaceans, fish eggs, small fish, the larvae of many sea creatures, and rarely other jellyfish. Around the world, there are jellyfish of many colors and shape which are controlled by their environment. Jellyfish are found in all of the Earth's oceans, including the very deep sea, as well as shallow saltwater lakes. Various jellyfish species have a wide range of living preferences, with some preferring arctic waters, and others preferring warmer tropical waters.

Sea anemones
They have a polypoid shape and are mostly sessile. However, all sea anemones have a sticky, muscular foot. This can enable them to move around and stick to a varied rock or even other animals. Most anemones prefer to stay stuck where they are. But some move by sliding along slowly on their feet. To eat, small fish, shrimp, or plankton get stung by it venom. It paralyzes the prey so the anemone can move it to the mouth for digestion inside the gastrovascular cavity.

True corals
These are marine invertebrates that comprise the great reefs of the sea. There are two types of true corals, which included octocorals (with eight body partitions), and hexacorals (with tentacles and partitions in multiples of six).

Sea pens
These are colonial marine invertebrates that produces in shallow and deep waters from polar seas to the tropics.Their shape and size looks like a quill pen, giving them the name sea pen.

Cubozoa
This lower classification consists of box jellies. In contrast from true jellyfish, box jellies maneuvers quickly, and their hood is in the shape of a cube. They also have four evenly shaped tentacles or a cluster of long tentacles in contrast between the true jellyfishes, and they inhibit a deadly venom.

​Hydrozoa
This classification is comprise of a diverse group of cnidarians, ranging from siphonophores, hydroids, fire corals, and many medusae.

Siphonophores
All siphonophores are predators, and use their many tentacles to capture crustaceans and small fish. They come in all shape and sizes, mimicking like jellyfishes or clusters of balls.

Hydroids
Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater Hydra are solitary, with the polyp attached directly to the substrate.