Phylogenetic Tree of Animals

Phylogenetic Tree of Animals

Eumetazoa

  • Defined by bilateral symmetry and being triploblastic.

  • Possession of a body cavity.

Major Groups

  • Choanoflagellata
      - Characterized by single flagellate organisms.
      - Exhibits motile flagellates.
      - Forms colony of cells that aggregate to form a hollow sphere.

  • Metazoa (Animals)
      - Classification includes:
        - Acoelomates: Organisms without a coelom.
        - Radiata: Exhibits radial symmetry and is diploblastic.
        - Parazoa: Organisms lacking true tissues.
        - Protostomia: Major subgroup of coelomates.
          - Ecdysozoa: Notable for molting (ecdysis).
          

Structural Features

  • Lophophore
      - Characteristic tentacles associated with feeding.
      - Apical tuft: Anterior arrangement of cilia which assists in feeding.

  • Body Structure
      - Mouth, gut, trunk, anus structure as follows:
        - Trunk is divided into anterior (mouth) and posterior (anus) sections.
        - Digestive system organized with a defined gut.

Lophotrochozoa Groups Include:

  • Arthropoda (Arthropods)

  • Nematoda (Roundworms)

  • Platyhelminthes (Flatworms)

  • Rotifera (Rotifers)

  • Ectoprocta (Bryozoans)

  • Brachiopoda (Brachiopods)

  • Annelida (Annelids)

  • Mollusca (Mollusks)

  • Chordata (Chordates)

Deuterostomia Groups Include:

  • Echinodermata (Echinoderms)

  • Acoela

  • Cnidaria (Cnidarians)

  • Placozoa

  • Basal

  • Porifera (Sponges)

  • Ctenophora (Comb Jellies)

Deuterostomes

Key Characteristics

  • Cleavage Type: Radial and indeterminate.

  • Anus Development: Anus develops at or near the blastopore; the mouth develops elsewhere.

  • Eucoelomate Formation: Achieved through enterocoely.

Notable Groups Include:

  • Echinoderms

  • Cephalochordates

  • Chordates

  • Urochordates

  • Vertebrates

Echinodermata

Overview

  • Include species such as sea stars, sea urchins, sea cucumbers, and sea lilies.

  • Unique characteristics:
      - Pentamerous radial symmetry as adults (not seen in larvae).
      - Internal skeleton composed of calcium-rich plates forming an endoskeleton with spines.
      - Features mutable connective tissue.
      - Exclusive to marine environments, incapable of osmoregulation.
      - Lack cephalization: possess a central nerve ring with branches instead.
      - Possess an extensive coelom housing a water vascular system.

  • Approximately 6,500 species documented.

Water Vascular System Structure

  • Madreporite: Entry point of the water vascular system.

  • Stone canal: Connects madreporite to ring canal.

  • Ring canal: Circulates water from the stone canal to radial canals.

  • 5 Radial canals: Extend into each arm of the starfish.

  • Lateral canals: Connect radial canals to tube feet.

  • Ampulla: Storage structures controlling tube feet extension.

  • Tube foot: Extension for locomotion and feeding.

  • Polian vesicles: Stores water for the system.

  • Tiedemann’s bodies: Structures associated with filtering system.

Additional Structures in Echinodermata

  • Pedicellariae: Minute pincers located on the aboral surface that serve to protect and clean, composed of movable ossicles.

  • Dermal Branchiae (Papulae): Projections of the coelomic cavity utilized for respiration and excretion.

  • Evisceration: Ability to expel internal organs in response to stress or predation.

  • Regeneration and Autotomy: Capabilities of regrowing lost parts; autotomy involves self-amputation of a limb.

Chordata - The Chorded Animals

Five Main Characteristics (Present in all members at some point)

  1. Notochord:
       - A dorsal elastic supporting rod extending along the length of the body.
       - Composed of a semi-rigid body of cells encased in a fibrous sheath, providing structural support and an axis for muscle attachment.

  2. Nerve Cord:
       - Dorsal, hollow, tube-like structure.
       - Anterior end enlarges to form the brain.

  3. Pharyngeal Pouches (Gills Slits):
       - Slit-like openings leading from the pharyngeal cavity to the exterior; originally functioning as a filter-feeding device.

  4. Tail:
       - A post-anal extension added behind the end of the digestive tract; has evolved for propulsion in aquatic environments.

  5. Endostyle/Thyroid Gland:
       - Secretes iodinated hormones involved in metabolism regulation.

Cephalochordata (Lancelets)

Characteristics

  • Size: Typically 5 to 7 cm in length.

  • Habitat: Marine environments, particularly sandy coastal waters.

  • Morphology: Elongated, fish-like organisms.

  • Development: Both the notochord and nerve cord extend the length of the body.

  • Adult Forms: Retain all five chordate characteristics.

  • Evolutionary Significance: Closest known relative of vertebrates, identified as a potential ancestor.

Urochordata (Tunicates)

Life Stages

  • Tadpole Larva: Exhibits all five chordate characteristics during its larval stage.

  • Adult Stage:
      - Encased in a protective tunic, exhibiting specialized sessile adaptations for filter feeding.
      - Retains pharyngeal gill slits and endostyle for feeding processes.

Evolutionary Importance

  • Considered a close ancestral form to vertebrates due to shared characteristics.

  • Paedomorphosis: An evolutionary process where larval or juvenile features are transitioned into adult forms of subsequent species descendants.

Chordate Origins

  • Lineage indicates that all chordates evolved from ancestral deuterostome origins.

  • Ancestry traced back to:
      - Cephalochordates
      - Urochordates
      - Echinoderms
      - Acknowledging Tadpole Larva as presenting key features that suggest a link to vertebrates.

  • Paedomorphosis once more highlighted as a critical evolutionary mechanism in this lineage.