BIL 106 - Lecture 15

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

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

Echinoderm-like characters:

its TORNARIA larva is very similar to the echinoderm larva

Chordate-like characters:

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.

PHYLUM CHORDATA - The Chordates Three Subphyla of Chordates:

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

And all 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)

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.