Animal Kingdom Classification: Vertebrates & Invertebrates

Animal Kingdom: Fundamental Characteristics

Animals are multicellular organisms that possess tissues, and their nutrition is heterotrophic, meaning they obtain nutrients by consuming other organisms.

Vertebrates: Animals with a Backbone

Vertebrates include:

• Fish
• Amphibians
• Reptiles
• Birds
• Mammals

They are characterized by having an internal skeleton that includes a vertebral column (backbone).

Invertebrates: Animals Without a Backbone

Invertebrates encompass a vast group, including:

• Porifera (Sponges)
• Coelenterata (Cnidarians)
• Worms
• Mollusks
• Arthropods
• Echinoderms

These animals may have an internal or external skeleton, or no skeleton at all, and they lack a vertebral column. They can be found in both freshwater and saltwater environments.

Porifera (Sponges): Simple Aquatic Animals

Porifera are marine aquatic animals with a soft body and numerous pores through which water circulates. Water exits through a larger opening called an osculum, which communicates with the exterior. Sponges have no specialized apparatus or organs and reproduce both asexually and sexually.

Coelenterata (Cnidarians): Tentacled Marine Life

Coelenterata are aquatic marine animals with a soft and translucent body. They possess a central mouth surrounded by tentacles. They typically exhibit two life phases:

• The polyp, which is sessile and attached to a substrate.
• The medusa (jellyfish), which is free-swimming and often reproduces asexually.

Worms: Diverse Forms and Habitats

Worms are characterized by their cylindrical or flat bodies. They inhabit various environments, including land, freshwater, and saltwater. Examples include Earthworms and Flatworms.

Echinoderms: Spiny-Skinned Marine Animals

Echinoderms are marine animals whose bodies are covered by protective plates and spines. A unique feature is their ambulacral system, which consists of vesicles and water-filled canals used for locomotion, feeding, and respiration.

Mollusks: Soft-Bodied Animals with Shells

Mollusks are soft-bodied animals distinguished by a muscular foot, a protective shell (in most species), and a visceral mass containing their organs. Some mollusks possess a small, toothed ribbon called a radula, used for feeding. They reproduce sexually. There are three main types:

• Bivalves
• Gastropods
• Cephalopods

Bivalves: Two-Shelled Marine Inhabitants

Examples include Clams. Bivalves have a divided shell, are marine, and respire through gills. Their foot is typically small.

Gastropods: Snails and Slugs

Examples include Snails and Conchs. Gastropods live in freshwater, on land, or in marine environments. They have a large foot used for crawling.

Cephalopods: Intelligent Marine Predators

Examples include Octopus. Cephalopods are marine animals whose foot is modified into tentacles surrounding their mouth. They have a distinct head and may possess an internal hard piece (like a pen or cuttlebone).

Arthropods: Segmented Bodies and Jointed Legs

Arthropods are animals characterized by an exoskeleton formed by articulated pieces and distinctive jointed legs. They inhabit diverse environments, and their diets are varied.

Arthropod Classification: Major Groups

Arachnida: Spiders and Scorpions

Examples include Spiders. Arachnids are terrestrial. Their head and thorax are fused, forming a cephalothorax. They typically have 8 legs.

Crustacea: Crabs, Lobsters, and Shrimp

Examples include Crabs. Crustaceans are primarily aquatic. They also possess a cephalothorax and typically have 10 legs.

Myriapoda: Centipedes and Millipedes

Examples include Centipedes. Myriapods are terrestrial. Their body is divided into many segments, with most segments having two pairs of legs.

Insects: The Most Diverse Group

Examples include Beetles. Insects have a body divided into three distinct parts: a head, thorax, and abdomen. They typically have 6 legs, 2 antennae, and 4 wings (though wing presence and form can vary).

Common Insect Orders

• Coleoptera (Beetles)
• Lepidoptera (Butterflies and Moths)
• Diptera (Flies and Mosquitoes)
• Hemiptera (True Bugs)
• Orthoptera (Grasshoppers and Crickets)
• Odonata (Dragonflies and Damselflies)
• Hymenoptera (Ants, Bees, and Wasps)

Many insects undergo metamorphosis, a significant change in form from their larval stage to adulthood.