Lecture Seventeen - Animal diversity III Flashcards
How did the mesoderm and coelom develop?
What are echinoderms?
Deutrostomes.
Secondary radial symmetry (5 limbs).
Calcarious skeletaton under skin.
Unique water vascular system.
Describe the phylum chordate.
Bilaterally symmetrical.
Triploblastic - three germ layers.
Coelomates.
Deuterostomes.
Characteristics:
Notochord = skeletal rod of fluid filled compartements.
Dorsal hollow nerve chrod = develops into the CNS.
Pharyngeal slits = pouches of the pharync forming structures to the out side. Used for feeding, gas exchange and bodily structures in some chordates.
Post anal tail = In some species, tail is greatly reduced in embryonic development. Provides propelling force in many aquatic chordates.
What are the four chordate characters?
1) Notochord = skeleton.
- Flexible but stiff rod of fluid filled compartments.
- Skeletal support for most of the length of the animal. - Present in the embryo.
- Most vertebrates develop a more complex, jointed skeleton with adult retaining only remnants of it.
2) Dorsal hollow nerve chord = nervous system.
- Develops form a plate of dorsal ectoderm that folds inward and rolls into a tube.
- Other animal phyla have solid nerve chords.
- Develops into the central nervous system
- > the brain and spinal chord.
3) Pharyngeal slits = feeding -> breathing -> other structures.
- Pouches of pharynx forming openings to the outside.
- Different functions in different groups.
- Suspension feeding structures (early chordates).
- Gas exchange (fish).
- Develop into parts of the ear, neck and head (tetrapods).
4) Post anal tail = locomotion.
- Muscular tail posterior to the anus.
- In some species, the tail is greatly reduced during embryonic development.
- Contains skeletal elements and metameric muscles.
- It provides propelling force in many aquatic species.
What are cephalochrodates (lancelets)?
Small (few cm) suspension feeders.
Retain basic characters of chordate body plan.
Gill slits have a feeding function.
Particles trapped in mucus.
Gas exchange by diffusion.
A small elongated marine invertebrate that resembles a fish but lacks jaws and obvious sense organs.
Lancelets possess a notochord and are among the most primitive chordates.
Are craniates vertebrates?
Shared characteristics include:
Head (skull)
Brain
Eyes
Other sensory structures
Duplications of developmental genes
A neural crest
Some, but not all, craniates are vertebrates.
Describe the Myxini (hagfish).
Deuterostomes.
Notochord retained in adults (cartilage) - no vertebrae.
No paired appendages.
Cartilagious skull.
No jaws.
Few species (30 or so) all marine. Is a craniate, but not a vertebrate.
Describe the subphylum vertebrata.
Craniates with a backbone - vertebrae.
Paired appendages.
- Pectoral fins ~ arms.
- Pelvic fins ~ legs.
Compare the different kinds of skeletons.
Hydrostatic = Heavy, flexible, cannot support body weight.
Exoskeleton = heavy, can support body weight, moulting necessary which leaves organism vulnerable, lighter than a hydrostatic skeleton.
Endoskeleton = light, can support body weight, can grow.
Describe the petromyzontida (lampreys).
Oldest vertebrate lineage still in existence.
No paired appendages.
No jaws.
Skeleton = notochord in larvae (filter feeders similar to lancelets), cartilage in adults.
Adult often parasitic.
Habitats = marine and freshwater.
Describe the development of paired fins.
Paired appendages marked the first step towards fin (and later limb) based locomotion.
Earliest vertebrate fossils lacked paired fins but some possessed ventro-lateral folds in body wall.
These were reduced to anterior and posterior pairs and stiffened by transverse series of endoskeletal elements.
Eventual extension of proximal elements forms supporting girdles.
Describe gnathostomes (jawed vertebrates). How did their jaws develop?
Most extant vertebrates are gnathostomes.
Many fossil groups - placoderms and acanthodians.
450-420 mya.
Extant groups = chondrichtyans, actynopterygii and sarcopterygii.
Jaws are hinged skeletal structures.
Usually have teeth.
Current theory:
- Skeletal rods between gill slits.
- Change of feeding method.
- Loss of and/or modification.
Important in vertebrate evolution:
- Exploit wider variety of food.
- Develop other structures.
Describe the class of Chondrichthyes (cartilaginous fish).
Skeleton predominantly composed of cartilage.
- Calcium may be present.
- Loss of ossified (boney) bone is derived a condition. Originate ~450mya.
Heavier than water, buoyancy from:
- Oil in large liver. Constant movement provides lift form pectoral fins and tail. E.g. Sharks, rays and skates.
Describe the class Actinopterygii (ray-fins).
Fins supported by dermal rays.
Mucles do not extend into fins.
Originate 400 mya.
Dominant class of vertebrates (27,000 species).
Habitat - marine and freshwater.
Describe the class Sarcopterygii (lobe fish).
Lobe finned:
- Rod shaped bones.
- Muscles.
Locomotion:
- Swimming.
- ‘walk’ under water.
Only a few species left:
- Coelacanths.
- Lung fish.
