Animal Biology Review

Kingdom Animalia

• Includes a variety of organisms such as flatworms, centipedes, millipedes, spiders, reptiles, mammals, birds, and insects.
• Key groups within Animalia include arthropods (crustaceans), annelids, mollusks, roundworms (nematodes), and vertebrates.
• Other groups mentioned are sponges, cnidarians, amphibians, fish, and echinoderms.
• Classified under broader categories like protostomes, deuterostomes, acoelomates, pseudocoelomates, and coelomates.
• Evolutionarily linked to an ancestral protista.

Animalia Characteristics

• All animals are multicellular, eukaryotic, and heterotrophic.
• Animals are capable of movement at some point in their life cycle.
• Animal cells have an outer cell membrane but lack a cell wall.
• Most animals reproduce sexually, although some can reproduce asexually.

Animal Cell Structures

• Key organelles include mitochondria, rough and smooth endoplasmic reticulum, ribosomes (both free and bound), plasma membrane, cytoplasm, microtubules (part of the cytoskeleton), lysosomes, centrioles, nucleus, nucleolus, chromatin, nuclear pore, nuclear envelope, and the Golgi complex.
• Levels of organization: Cells → Tissues → Organs → Organ Systems → Organism.

Invertebrates vs. Vertebrates

• Approximately 95% of all animals are invertebrates.
• Invertebrates comprise over 90% of all animal species, including insects (49.8%), crustaceans (29.9%), chelicerates, myriapods, mollusks, and echinoderms.
• Vertebrates include fish, mammals, reptiles, birds, and amphibians.

Body Structure and Support

• Exoskeletons: Tough outer coverings that provide protection and prevent water loss; they must be shed as the animal grows (molting); found in invertebrates except echinoderms.
• Endoskeletons: Internal support frameworks found in vertebrates and echinoderms.
• Vertebrate endoskeletons consist of a backbone, with material varying: echinoderms use calcium carbonate, sharks use cartilage, and mammals use bone.

Animal Habitats

• Marine environments, including coral reefs and the benthic zone.
• Freshwater environments like rivers, streams, lakes, and ponds.
• Terrestrial environments such as deserts, grasslands, rainforests, and polar caps.

Animal Reproduction

• Asexual reproduction methods: budding, regeneration, and fragmentation.
• Mostly reproduce sexually via eggs and sperm.
• Some animals are hermaphrodites (e.g., earthworms), producing both eggs and sperm.

Animal Fertilization

• Internal Fertilization: Sperm and egg join inside the animal’s body, forming a zygote.
• External Fertilization: Sperm and egg join outside the animal’s body; requires an aquatic environment.

Animal Development

• Zygote undergoes mitosis to form an embryo.
• Development from two cells to a solid ball of cells.
• Formation of a blastula: a fluid-filled sphere of cells, described as a "hollow bubble".
• Formation of a gastrula: cells pinch inward, creating a "double bubble" structure.

Gastrulation and Cell Layers

• Cell layers of the gastrula develop into tissues.
  • Endoderm: Inner cell layer, forming digestive organs and digestive tract lining.
  • Mesoderm: Middle cell layer, forming muscle tissue and various systems.
  • Ectoderm: Outer cell layer, forming the skin.

Animal Evolution and Classification

• Animals are classified by body cavities, tissue layers, reproduction, development, digestion, symmetry, and anatomical features.
• Key classifications: Parazoa, Radiata, Bilateria, Protostomia, Deuterostomia, Ecdysozoa, Lophotrochozoa.

Evolutionary Traits

• Evolutionary trajectory:
  • Ancestral protozoan → sponges (no true tissues, multicellularity) → cnidarians (tissues, radial symmetry) → flatworms (acoelomate body cavity, bilateral symmetry) → roundworms (pseudocoelom) → rotifers, mollusks, annelids, arthropods (coelom, protostome development, segmentation) → echinoderms, chordates (deuterostome development, segmentation).

Animal Symmetry

• Symmetry: the similarity or balance among body structures of organisms.
  • Asymmetry: no symmetry (e.g., sponges).
  • Radial Symmetry: Body can be divided along any plane through a central axis into roughly equal halves (e.g., jellyfish, starfish, anemone).
  • Bilateral Symmetry: Body can be divided into mirror image halves only along one plane through the central axis (e.g., beetles).

Asymmetry

• Body cannot be divided evenly across a central plane or axis.
• Example: Sponges.

Radial Symmetry

• Body can be divided along any plane, through a central axis, into roughly equal halves.
• Examples: Jellyfish, Starfish, Anemone.
• Typically found in slow-moving organisms.

Radial Symmetry Body Plan

• Surface Terms:
  • Oral Surface: Surface with the mouth (underside).
  • Aboral Surface: Surface opposite the mouth.
• Example: Regular Echinoid (Strongylocentrotus)

Bilateral Symmetry

• Body can be divided into mirror image halves only along one plane through the central axis.
• Characteristic of many animals, including humans.

Bilateral Body Plan

• Exhibits cephalization (“head end” with concentrated nervous tissue).
• Anatomical terms: Anterior (head end), Posterior (tail end), Dorsal (backside surface), Ventral (belly/underside surface).

Comparing Invertebrate Animals

• Porifera (Sponges):
  • Simple, pore-bearing animals; asymmetrical or radial symmetry.
  • Filter feeding; digestion occurs via diffusion.
  • No nervous system; asexual and sexual reproduction.
  • Sessile (non-motile).
• Cnidaria (Jellyfish, Sea Anemones, Corals, Portuguese Man-of-War):
  • Have stinging cells (cnidocytes); radial symmetry.
  • Digestive cavity with one opening; circulation via diffusion.
  • Nerve net; asexual and sexual reproduction.
  • Muscles; two forms: polyps and medusa.
• Worms (Flatworms, Roundworms, Segmented Worms):
  • Bilateral symmetry, cephalization.
  • Digestive cavity (1 opening) or digestive tract (2 openings); simple diffusion or closed circulatory system.
  • Ganglia (cephalization), primitive brain; asexual, sexual, and hermaphroditic reproduction.
  • Muscles; first to have bilateral symmetry, segments, organs, cephalization, and separate sexes.
• Mollusca (Snails, Slugs, Clams, Oysters, Scallops, Mussels, Squid, Octopus):
  • Soft-bodied animals; bilateral symmetry, cephalization.
  • Digestive tract (2 openings); simple diffusion or closed circulatory system (squid, octopus).
  • Brain; sexual reproduction, hermaphroditic and separate sexes.
  • Known for muscular foot; medical research for anti-cancer drugs, environmental monitors (filter feeders).
• Echinodermata (Starfish, Sea Urchins, Sand Dollars, Sea Cucumbers):
  • Spiny skin; 5-part radial symmetry, bilateral larvae.
  • Digestive tract (2 openings); water vascular system.
  • Nerve ring; sexual reproduction, external fertilization.
  • Endoskeleton and water vascular system; regenerate, all marine, defense mechanisms (spines, shedding of arms, evisceration).
• Arthropoda (Crayfish, Crabs, Butterflies, Spiders, Scorpions, Beetles):
  • Jointed appendages; bilateral symmetry, cephalization.
  • Digestive tract (2 openings); open circulatory system.
  • Brain; sexual reproduction, internal and/or external fertilization.
  • Exoskeleton and muscles; molt to grow, exoskeleton made of chitin, land and water animals.

Additional Notes of Vertebrates

• Fish: Aquatic animals with gills that can adjust their body temperature through their external environment. Example: Angel fish.
• Amphibia: Start their life cycle underwater and move to land. Generally carnivorous while in the water, many undergo metamorphosis. Example: Salamander, Frog (Order Anura - tailless).
• Reptilia: Tetrapods (four legs or leg-like appendages) with three-chambered hearts (except crocodiles, which have four). Eyes are important sense organs. Example: Crocodile, Alligator. (Cold Blooded)
• Aves: Vertebrates with feathers, a strong skeleton, and large muscular stomachs. (Warm Blooded) Example: eagle, Penguin
• Mammalia: Have four heart chambers, hair, three middle ear bones, sweat glands, and endothermic body plan. Example: Chimpanzee, Koala.