Concepts that Guide Zoologists’ Thinking: include that of unifying traits and diversifying variations of animal life, including protozoa, cell, food gatherer, phylum, class, order, family, genus, species, morphology (systems of muscles or bones), histology (body tissues), cytology (cells and their components), neurology, embryological origin, animal physiology, anatomy, homeostasis, heredity, genetics, ecology, biochemistry, invertebrate zoology, entomology (insects), malacology (mollusks), vertebrate zoology, ichthyology (fish), herpetology (amphibians and reptiles), ornithology (birds), mammalogy (mammals), vertebrate zoology.