Distinguishing Characteristics

In the animal kingdom, there are several distinguishing characteristics that set them apart from other organisms in different kingdoms of life. Animals are multicellular eukaryotes, which means that they are made up of multiple cells and their cells have a nucleus and other membrane-bound organelles. Additionally, animals are ingestive heterotrophs, meaning they obtain their energy by consuming other organisms.

One key characteristic that separates animals from one another is whether or not they have a backbone. Invertebrates are animals without a backbone, which makes up between 95 and 99 percent of all animal species. Invertebrates tend to have an exoskeleton, a hard or tough outer covering that provides support, protects body tissues, prevents water loss, and protects the organism from predation. On the other hand, vertebrates are animals with an endoskeleton and a backbone, which includes fish, amphibians, reptiles, birds, and mammals.

Embryonic Development

In sexual reproduction, a zygote is formed when a sperm cell penetrates an egg. The zygote is the first cell stage and eventually develops into an embryo. The two-cell stage is known as an embryo, and the blastula is a fluid-filled ball of cells formed by mitotic cell division of the embryo. The gastrula is a two-cell-layer sac with an opening at one end that forms from the blastula during embryonic development. The inner layer of cells in the gastrula that develops into digestive organs and the digestive tract lining is called the endoderm, while the outer layer of cells in the gastrula that develops into nervous tissue and skin is called the ectoderm. The layer of cells between the endoderm and the ectoderm that can become muscle tissue and tissue of the circulatory, respiratory, and excretory system is called the mesoderm.

Symmetry

Symmetry is another characteristic that sets animals apart from one another. Radial symmetry is a body plan that can be divided along any plane, through a central axis, into roughly equal halves. An example of an animal with radial symmetry is a starfish. Bilateral symmetry is a body plan that can be divided into mirror images along only one plane through the central axis. Animals with bilateral symmetry have an anterior, which is towards the head end, and a posterior, which is away from the head end. The tendency to concentrate sensory organs and nervous tissue at an animal's anterior end is known as cephalization. The backside of an animal with bilateral symmetry is called the dorsal side, while the underside or belly is called the ventral side.

Body Cavity

Animals can also be classified based on the type of body cavity they possess. The coelom is a fluid-filled body cavity completely surrounded by mesoderm, while the pseudocoelom is a fluid-filled body cavity between the mesoderm and the endoderm. An animal with a solid body that lacks a fluid-filled body cavity between the gut and the body wall is called an acoelomate. Additionally, animals can be classified as either protostomes or deuterostomes. A protostome is a coelomate animal whose mouth develops from the opening in the gastrula, while a deuterostome is a coelomate animal whose anus develops from the opening in the gastrula.

Fish

Fish, a type of vertebrate, have unique characteristics that set them apart from other animals. Fins are paddle-shaped structures used for steering, balance, and propulsion. Scales are small, flat, plate-like structures near the surface of the skin of most fishes. The operculum is a movable, protective flap that covers a fish's gills and helps to pump water that enters the mouth and moves over the gills to allow for gas exchange. Fish also have a lateral line system, which is a series of sensory organs that detect pressure changes and vibrations in the water. Additionally, fish are ectothermic, meaning their body temperature is determined by the temperature of their environment.

Amphibians

Amphibians, another type of vertebrate, have a unique life cycle that involves both aquatic and terrestrial environments. They typically begin their lives as aquatic larvae, breathing through gills, and eventually metamorphose into adults that breathe through lungs and their skin. Amphibians have moist skin that helps them breathe, and many species have toxins in their skin as a defense mechanism.

Reptiles

Reptiles, including snakes, lizards, turtles, and crocodilians, are also vertebrates with unique characteristics. Reptiles are ectothermic, meaning their body temperature is determined by their environment, and most have dry, scaly skin that helps prevent water loss. Reptiles also have a three-chambered heart, except for crocodilians, which have a four-chambered heart. Additionally, reptiles lay eggs with a leathery or hard shell, which protects the developing embryo.

Birds

Birds, another type of vertebrate, are endothermic, meaning they can regulate their body temperature internally. They have feathers that provide insulation and aid in flight, and their bones are hollow and lightweight to aid in flight as well. Birds also have a four-chambered heart, and their respiratory system is unique in that they have air sacs that allow for more efficient gas exchange during flight.

Mammals

Mammals, the final type of vertebrate, are endothermic and have hair or fur on their bodies. They also have mammary glands that produce milk to nourish their young. Mammals have a four-chambered heart, and their respiratory system includes lungs and a diaphragm to aid in breathing. Additionally, mammals have different types of teeth specialized for different functions, such as tearing, crushing, and grinding.

Summary

In summary, the animal kingdom is diverse and encompasses a wide range of organisms with unique characteristics. Animals can be distinguished by whether they have a backbone, their symmetry, their body cavity type, and their embryonic development. Vertebrates, a subset of animals, include fish, amphibians, reptiles, birds, and mammals, each with their own unique features and adaptations."

Invertebrates

Distinguishing Characteristics

Invertebrates are animals without a backbone, which makes up the vast majority of all animal species. They are incredibly diverse and are found in a variety of habitats, from the depths of the ocean to the soil in your backyard. Invertebrates can be grouped into several different phyla, each with their own unique characteristics.

Arthropods

One of the largest phyla of invertebrates is the arthropods, which includes insects, spiders, crabs, and other animals with jointed legs and a hard exoskeleton. Arthropods have been incredibly successful in colonizing different environments and make up the majority of animal species on Earth. They play important roles in ecosystems as pollinators, predators, and decomposers.

Mollusks

Another phylum of invertebrates is the mollusks, which includes snails, clams, and squids. Mollusks are known for their soft bodies and hard shells, which are used for protection. They have a muscular foot that they use for movement and a radula, a tongue-like structure covered in tiny teeth that they use for feeding.

Echinoderms

Echinoderms, such as starfish and sea urchins, are a unique group of invertebrates that have radial symmetry and a water vascular system. They move using hundreds of tiny tube feet and are important members of marine ecosystems.

Worms

Worms, such as earthworms and leeches, are another phylum of invertebrates. They have long, slender bodies and are important decomposers in soil and aquatic environments.

Summary

Overall, invertebrates are incredibly diverse and play important roles in ecosystems and scientific research.