Animal Kingdom Classification: A Comprehensive Guide

Mollusks

Triploblasty, coelomates, not segmented. Bilateral symmetry. Soft body (head, visceral mass, foot). Limestone shell. Complete digestive tube (mouth-anus). Radula (in most). Open circulatory system (closed in cephalopods). Excretory system: 1 or 2 metanephridia. Ganglionic nervous system. Asexual or larval reproduction.

• Bivalves: Mussels
• Gastropods: Snails
• Cephalopods: Cuttlefish

Annelida

Triploblasty, coelomates. Bilateral symmetry. Elongated cylindrical body with rings or metamerism. Closed circulatory system. Ganglionic nervous system. Cutaneous respiration. Excretory system: metanephridia. Sexes separate or hermaphrodites. With or without a larval stage.

• Polychaetes: Marine worms
• Oligochaeta: Earthworms
• Hirudinea: Leeches

Arthropods

Triploblasty, coelomates. Bilateral symmetry. Body divided with jointed appendages (wings, legs, or antennae). Exoskeleton of chitin. Complete digestive system. Open circulatory system. Respiration: gills, trachea, or book lungs. Excretory system: Malpighian tubules or green glands. Ganglionic nervous system. Well-developed senses. Endocrine system controls reproduction. Mostly oviparous, some viviparous (e.g., scorpions). Development: egg-larva-pupa-adult.

• Arachnids
• Crustaceans
• Insects
• Myriapoda: Centipedes

Echinodermata

Triploblasty, coelomates. Radial symmetry. Endoskeleton. Nerve ring around the mouth and radial nerves. Water vascular system with tube feet. Poorly developed circulatory system. No excretory system (waste expelled through the epidermis). Respiration through gills and tube feet. Sexual reproduction. External fertilization. Some can reproduce asexually (e.g., starfish).

• Echinoids: Sea urchins
• Asteroidea: Starfish

Chordata

Triploblasty, deuterostomes. Bilateral symmetry. Well-developed coelom. Complete digestive tube with mouth and anus. Closed circulatory system. Heart is ventral to the digestive tract. Endoskeleton (cartilaginous or bony). Sexual reproduction. Separate sexes.

Vertebrates

Internal skeleton (axial, appendicular). Body with head, trunk, and tail. Nervous system: Brain, spinal cord. Digestive system: Complete tube with associated glands. Respiratory system: Gills, lungs. Closed circulatory system: Heart, arteries, capillaries. Lymphatic system: Vessels, capillaries, lymph nodes. Urinary system: Kidneys, nephrons. Sexual reproduction. Mostly oviparous, some viviparous. Skin with epidermis and dermis.