The acorn worms are rather nondescript, vermiform creatures that spend
their lives burrowing through muddy substrate in detritivorous bliss.
And all share the following synapomorphies that set them apart from
other animal phyla:
Kingdom Animalia: Subkingdom Eumetazoa, Bilateria, Deuterostomia, Phylum
Chordata, Subphylum Vertebrata
Vertebrates share synapomorphies with each other that the Cephalochordata
Urochordata (tunicates) lack:
internal skeleton constructed of bone
articulated, dorsal vertebral column housing the nerve cord (except
bony cranium housing the brain
dorsal, hollow nerve cord develops from special embryonic neural
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
- Highly specialized and differentiated central nervous system
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)
- 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
- 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.