The word “animal” refers to any member of the animal kingdom with a nervous system capable of moving, eating, breathing, and feeling. Humans are mammals, a class of mammal which includes all vertebrate animals. Other animals are unicellular, meaning they are not multicellular. They are made up of cells with a single nucleus and a series of organs including a gill, mouth, anus, and genitalia. Humans can be classified as bony animals, owing to the fact that their bones are made up of very small bones called osteoderms.

Animals are classified into four major classes: land animals, sponges, marine animals, and invertebrates. Animals are classified by how they move, their organs, and their mode of reproduction. Humans are an animal, as we know ourselves, and all other animals are classified into one of these four major categories based on their arrangement in nature. Humans are mammals, another class of mammal which includes all of the animals with a nervous system capable of moving, breathing, and changing shape; although, humans are not considered a true animal, due to the fact that we are covered with fur, a type of dense, insulating material.

Cephalopods, include some of the animals with a nervous system, including molluscs, snails, squids, oysters, clams, and corals. These animals have gills that allow them to absorb water and breathe atmospheric air, which is their only means of survival. All cephalopods have cell walls, and these cell walls are composed of meshlike proteins. Multicellular organisms are animals with a cell wall composed of multiple protein complexes rather than a single protein.

The other animals commonly classified under Cephalopoda are the Blastula (elephants, since they give birth to a baby in an instant), Amniotic fluid-producing animals such as sheep, cattle, horses, ostriches, monkeys, parrots, cats, dogs, hamsters, guinea pigs, and the ovary-producing glands of females. Blastula do not have nervous systems but are instead born with an egg, forming a zygote (a kind of baby) which will then be enveloped in amniotic fluid. When fertilized by a male sperm and an egg produced by a female sperm, these zygotes will then fuse together and create a living embryo.

Most animals belong to one of the three basic types of animals: land animals (plant and animal), aquatic animals (plant and animal), and semi-precious/fish-based animals (mammal, reptile, fish). Animals within each class have different traits, and the latter two are classified according to whether or not they consume organic matter (inorganic or organic). Virtually all animals consume both organic and inorganic matter, which means that they can be divided into three broad categories: animals that eat either completely (e.g., cows, pigs, chickens, etc. ), animals that partially consume (e.g., whales, birds, balegards, turtles, etc. ), and animals that completely consume (e.g., omnivores, carnivores, herbivores).

The phylum Porifera, which includes all the classes mentioned so far, is the only animal kingdom in which all animals are considered to be members. The four phylum Porifera include twenty-eight different animal species, including twelve true poriferan species. One of the five recognized phylum crustaceans is the testudines (e.g., movies, zebra fish, cephalopods, shrimp, etc.). A few crustaceans have closed shells (e.g., cut shrimp, mollusks, crabs, snails, etc. ).