animals

Synapomorphies: Shared derived characteristics.
  - Lophophore: A feeding structure found in some aquatic invertebrates, characterized by ciliated tentacles.
  - Trochophore: A type of larval stage common in lophotrochozoans; has prototroch and telotroch for locomotion.
  - Spiral Cleavage: A developmental process where cells divide at an angle, resulting in a coiled pattern of cells.

General Characteristics:
- Small, multicellular, and complex microscopic animals.
- Exhibit a psuedocoelomate body plan.
Mastax: A muscular pharynx used for grinding food particles.
Habitat: Found in marine or freshwater environments, they are primarily filter-feeders.
Protonephridia: Excretory structures that function in osmoregulation.
Reproduction: Often exhibit parthenogenesis, allowing females to reproduce without fertilization.
- Corona/Wheel Organ: A structure with cilia that creates water currents for feeding.

General Characteristics:
- Acoelomate (lack a true coelom).
- Have protonephridia for excretion.
Classes:
  - Class Turbellaria: Free-living flatworms, such as planarians.
  - Class Trematoda: Flukes; parasitic flatworms typically possessing complex life cycles.
  - Class Monogenea: Monogenic flukes, usually ectoparasites of fish.
  - Class Cestoda: Tapeworms, characterized by a scolex (attachment organ) and proglottids (body segments).

Phylum Mollusca: Mollusks
- Notable features include a radula (a toothed structure for feeding) and a mantle (a significant body part that can form shells).
Classes:
  - Class Gastropoda: Univalves (single shell) or reduced/missing shells (e.g., snails, slugs).
  - Class Bivalvia: Clams and oysters; lack a head and radula; have two shells.
  - Class Cephalopoda: Includes cuttlefish, octopus, and squid; generally have reduced shells.
    - Notable Species: Chambered Nautilus (Nautilus).

Phylum Annelida: Annelids
General Characteristics:
- Metameric segmentation (body divided into segments).
- Organs and systems repeated in each segment, contributing to coelomate body plan.
Classes:
  - Class Polychaeta: Diverse; many are burrowing or filter-feeders and possess paired parapodia for movement.
    - Polyphyletic in nature.
  - Class Oligochaeta: Includes earthworms; paraphyletic group without parapodia.
  - Class Hirudinea: Leeches, often used in medicine for bloodletting.

Synapomorphies: Characteristics including a nonelastic cuticle or exoskeleton.
Molting/Ecdysis: The process of shedding the exoskeleton to allow for growth.

General Characteristics:
- Have a collagenous cuticle and longitudinal muscles only; pseudocoelomate body plan.
- Many are parasitic, affecting plants and animals.
Notable Species:
  - Ascaris: Intestinal roundworm.
  - Trichinella: Causes trichinosis; muscle parasites in humans.
  - Enterobius: Pinworm, common in humans.

Phylum Arthropoda: Arthropods
- Characteristics include jointed legs and a chitinous exoskeleton.
- Metameric Segmentation: Body organized into segments.
General Features:
- Open circulatory system for nutrient transport.

Characteristics:
  - Possess chelicerae (mouthparts).
  - Two tagmata: cephalothorax and abdomen.
  - Have six pairs of limbs (e.g., arachnids).

General Features:
- Comprises three tagmata: head, thorax, and abdomen.
- Ancestrally biramous appendages (two-branched).
Classes:
- Class Malacostraca: Includes large crustaceans (crabs, lobsters).
- Class Insecta: Insects; have three tagmata and features like tracheae and Malpighian tubules for respiration and excretion.

General Characteristics:
- Endoskeleton composed of calcareous ossicles; can be articulated or fused.
- Contains a water-vascular system with a complex network of canals facilitating movement.
Classes:
  - Class Asteroidea: Sea stars and sun stars, capable of regeneration.
  - Class Ophiuroidea: Brittle stars, have long, slender arms.
  - Class Echinoidea: Sea urchins and sand dollars; Aristotle’s lantern is a notable feeding structure.
  - Class Holothuroidea: Sea cucumbers, soft-bodied and can extrude their internal organs when threatened.
  - Class Crinoidea: Sea lilies, filter feeders that live anchored to the sea floor.

General Characteristics:
- Over 60,000 species characterized by the presence of a dorsal hollow nerve cord, notochord, post-anal tail, and pharyngeal slits during some stage of development.
Subphylum Urochordata:
- Includes sea squirts; exhibit a motile larval form and have a tunic made of cellulose known as tunicates.
Subphylum Craniata (Alt. name: Vertebrata)
  - Contains vertebrates with a complex brain and a closed circulatory system.
  - Hierarchy:
    - Superclass Agnatha:
      - Class Myxini: Hagfish, jawless fish.
      - Class Petromyzontes: Lampreys; also jawless.
    - Superclass Gnathostomata: Jawed vertebrates.
      - Class Chondrichthyes: Cartilaginous fish (sharks and rays).
      - Class Actinopterygii: Ray-finned fishes.
      - Class Sarcopterygii: Lobe-finned fishes; paraphyletic group containing ancestors of tetrapods.
        - Lineages: Actinistia (coelacanths), Dipnoi (lungfish), Tetrapods (four-legged vertebrates).
      - Class Amphibia: Amphibians, transition between water and land.
      - Class Mammalia: Mammals with features such as fur or hair and milk production.
      - Class Reptilia: Reptiles; paraphyletic due to its most basal forms.
      - Class Aves: Birds, evolved from theropod dinosaurs.