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Kingdom Animalia: Subkingdom Eumetazoa, Bilateria, Deuterostomia

THE DEUTEROSTOMES

Like the protostomes, the deuterostomes are

  • bilaterally symmetrical
  • triploblastic
  • coelomate

    But unlike the protostomes, in deuterostomes

  • blastopore becomes the anus (secondary opening becomes the mouth)
  • coelom derived via enterocoely
  • cleavage is radial and indeterminate
  • nervous system is primitively dorsal
  • circulatory system is primitively ventral

    PHYLUM ECHINODERMATA - The Spiny-skinned Animals

    What's an echinoderm?

    Let's look at the anatomy.

    An echinoderm is...

  • A slow-moving, pentaradially symmetrical deuterostome animal
  • has an internal skeleton constructed of calcium carbonate plates called OSSICLES
  • Larva is bilaterally symmetrical. Various larval types occur, with the most primitive larvae in the most primitive classes.
  • Coelom is highly derived WATER VASCULAR SYSTEM used for locomotion & feeding

    Echinoderm Diversity: The Most Familiar Groups

    PHYLUM HEMICHORDATA - The Acorn Worms

    This group is of interest primarily because it has characteristics linking it to both the echinoderms and the chordates.

  • Echinoderm-like characters:

  • Chordate-like characters:

    The acorn worms are rather nondescript, vermiform creatures that spend their lives burrowing through muddy substrate in detritivorous bliss.

    PHYLUM CHORDATA - The Chordates

    Three Subphyla of Chordates:

    And all share the following synapomorphies that set them apart from other animal phyla:

    Have a look at Chordate Phylogeny to better understand their evolutionary relationships.

    Kingdom Animalia: Subkingdom Eumetazoa, Bilateria, Deuterostomia, Phylum Chordata, Subphylum Vertebrata

    Let's meet the Vertebrates

    Vertebrates share synapomorphies with each other that the Cephalochordata (lancelets) and Urochordata (tunicates) lack:

  • internal skeleton constructed of bone
  • articulated, dorsal vertebral column housing the nerve cord (except hagfishes)
  • bony cranium housing the brain
  • dorsal, hollow nerve cord develops from special embryonic neural crest cells. Each subtaxon within Vertebrata has synapomorphies that set its members apart from the other vertebrates, and the specifics of some of these phlyogenies are still being argued. As we take a tour of each group, you'll notice these similarities and differences.

    THE VERTEBRATE BAUPLAN: How are we built?

    Vertebrate tissues, organs, and organ systems
    • Two-layered integument: epidermis above, dermis below. The epidermis is ectodermal; the dermis is mesodermal, and made primarily of connective tissue

    • Integument may have specialized derivatives such as scales, feathers, hair, claws, horns, glands, etc.

    • All surfaces lined by epithelium (of which epidermis is one type)

    • Endoskeleton made of bone, cartilage, and connective tissue

    • Muscular pharynx with multiple slits
      • in fishes, these bear the respiratory organs, the gills and the arches of the aortas (arteries exiting the heart)
      • in tetrapods, the gill branches give rise to glandular tissue, and in mammals, to the bones of the inner ear.

    • articulated vertebral column

    • bony cranium encasing the brain

    • a (primitively) ventral heart consisting of at least one ventricle and one atrium (heart chambers)

    • a closed circulatory system of
      • arteries - carry newly oxygenated blood from the heart to the rest of the body
      • veins - carry unoxygenated blood from the body back to the heart, via the lungs

    • Coelom encloses the internal organs
      • pericardium surrounds the heart
      • peritoneum surrounds the viscera

    • Three different types of muscle, each with a specific function.

    • Muscles are attached via TENDONS to bones, and move the skeleton. (Ligaments connect bone to bone.)

    • Paired kidneys remove nitrogenous waste from the bloodstream

    • Complex, sophisticated NERVOUS SYSTEM
      • Highly specialized and differentiated central nervous system (CNS) consisting of BRAIN and spinal cord.
      • PERIPHERAL NERVOUS SYSTEM consisting of 10-12 cranial nerves (originating directly from the brain), spinal nerves (originating from the spinal cord) and ganglia (nerves not directly connected to the CNS)
      • High degree of cephalization with paired sense organs for
        • complex vision
        • olfaction/chemoreception (smell and taste)
        • hearing
        • balance
    • Neurons (nerve cells) sheathed in a fatty substance called myelin, which increases the speed and efficiency of nerve signal transmission.

    • Endocrine system: ductless glands throughout the body, the products of which are transported by the circulatory system.
    • Sexually reproducing (at least primitively)
    • Bauplan: head, trunk, postanal tail. (Neck and appendages are extra!)
      • Note: In mammals only, the trunk is divided by the flat, muscular diaphragm into the thorax ("chest") and abdomen ("belly"). The diaphragm is responsible for inflation and deflation of the lungs, and mammals are the only vertebrates that have this muscle.