But unlike the protostomes, in deuterostomes

PHYLUM ECHINODERMATA - The Spiny-skinned Animals

Let's look at the anatomy.

An echinoderm is...

• water intake via the aboral madreporite
• water distributed radially via the
  • stone canal
  • ring canal
  • radial canals
  • tube feet
  The water vascular system is used, not for circulation, but for locomotion, as this MOVIE shows.
• Complete digestive tract, with anus generally on aboral side, away from the substrate
• Excretory system is secondarily lost
• Reduced circulatory system, composed of coelomic tissue, but NOT related to the water-vascular system
• Nervous system diffuse and decentralized, as is typical in radially symmetrical animals.
• Mostly dioecious with direct or indirect development

Echinoderm Diversity: The Most Familiar Groups

• Class Crinoidea - Sea lilies
• Class Asteroidea - Sea Stars
• Class Ophiuroidea - Brittle (or "Serpent") Stars
• Class Echinoidea - Sea Urchins & Sand Dollars
• Class Holothuroidea - Sea Cucumbers

PHYLUM HEMICHORDATA - The Acorn Worms

• its TORNARIA larva is very similar to the echinoderm larva

• ciliated, pharyngeal gill slits
• dorsal, sometimes hollow nerve cord (homology with chordate nerve cord uncertain)

The acorn worms are rather nondescript, vermiform creatures that spend their lives burrowing through muddy substrate in detritivorous bliss. You'll see them in lab.

PHYLUM CHORDATA - The Chordates

• Subphylum Urochordata - The Tunicates
• Subphylum Cephalochordata - The Lancelets
• Subphylum Vertebrata - The Vertebrates

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

• pharyngeal gill slits present during some stage of development
• dorsal, cartilaginous notochord at some stage of development
• dorsal, hollow nerve cord
• having an endostyle (Urochordata, Cephalochordata) or homologous thyroid gland (Vertebrata)
• tail posterior to the anus (primitively muscular and used for locomotion)

What Sets Vertebrates Apart from Other Chordates?

Vertebrates share the following synapomorphies with each other (with respect to the Cephalochordata and Urochordata, which lack these characters):

• skeleton constructed of bone
• articulated, dorsal vertebral column housing the nerve cord
• bony cranium housing the brain

THE VERTEBRATE BAUPLAN: How are we built?

• 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 animals that have this muscle.

• 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 well-developed epithelium (of which epidermis is one type)

• Endoskeleton made of bone, cartilage, and connective tissue
  • articulated vertebral column
  • bony cranium encasing the brain

• 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.

• a (primitively) ventral circulatory system
  • 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 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)
  • neurons (nerve cells) sheathed in a fatty substance called myelin, which increases the speed and efficiency of nerve signal transmission.
  • High degree of cephalization with paired sense organs for
    • vision
    • olfaction/chemoreception
    • hearing
    • balance

• Endocrine system: ductless glands throughout the body, the products of which are transported by the circulatory system. Hormones may be
  • peptides (short sequences of amino acids)
  • proteins (longer sequences of amino acid w/ complex structure
  • glycoproteins (protein/carbohydrate complex)
  • amines (single amino acid-like compound)
  • steroids (a lipid characterized by a carbon "skeleton" consisting of four rings with various functional groups attached to those rings)

• Sexually reproducing (at least primitively), though there are derived "variations on the theme":
  • parthenogenesis (from the Greek for "virgin birth")
    • Cnemidophorus spp.
    • in the "inverts," animals develop from haploid, unfertilized ova. In vertebrates, however, haploidy doesn't work. Adult females develop from diploid "zygotes" that have undergone chromosomal doubling after meiosis.
  • sequential hermaphroditism, in which an individual reverses its sex during its lifetime:
    • protogynous (female first, switching to male later)
    • protandrous (male first, switching to female later)
  (A note about the relative sizes of male and female animals...)