Chordates, Urochordates Flashcards
What are cephalochordates?
Subphylum – lancelets/amphioxus/branchiostoma
They are characterized by a notochord and have existed since the Middle Cambrian, approximately 505 million years ago.
What is the larval stage of cephalochordates like?
Free swimming, feed on plankton, stick into sand with tentacle to attract water
The larvae are mobile and actively feed on plankton.
What distinguishes adult cephalochordates?
Sedentary
They remain in one place as adults.
What is a notochord?
Stiffening rod to hold shape, precursor of a backbone
The notochord is a defining feature of chordates.
What are gill slits in cephalochordates similar to?
Human embryos
This similarity indicates a shared evolutionary ancestry.
What are urochordates also known as?
Tunicates/sea-squirts
They are a group of marine animals within the chordates.
Why are fossil tunicates rare?
Found in maotianshan shale, body plan hasn’t changed in 520 million years
This indicates a long evolutionary stasis.
How does the body plan of urochordate larvae compare to adults?
Body plan changes drastically
This metamorphosis reflects significant developmental changes.
What are the two theories regarding the evolution of vertebrates?
- Evolution from lancelet ancestor and tunicates
- Evolution from tunicate ancestor to lancelet-like species to vertebrates
These theories are highly debated among scientists.
What is the current consensus on the ancestor of vertebrates?
Tunicate ancestor
Evidence indicates that tunicates share a more recent common ancestor with vertebrates.
What do all chordates possess?
- Notochord
- Dorsal hollow nerve
- Post-anal tail
- Pharyngeal slits
These four features are defining characteristics of the phylum Chordata.
What are the derived characteristics of craniates?
- 2 sets of Hox genes
- Evolution of neural crest
Hox genes are crucial for body plan development, while the neural crest gives rise to various anatomical features.
What does the neural crest give rise to?
- Teeth
- Parts of skull
- Inner layer of facial skin
- Types of neuron
Neural crest cells are pivotal in the development of many structures in vertebrates.
What defines craniates?
Chordates with a head
This group includes all vertebrates and some non-vertebrate chordates.
What is significant about the Maotianshan shales?
530 million years ago – Cambrian explosion
This period marks a significant increase in the diversity of life forms.
What is Haikouella?
Lancelet-type organism with brain and paired eyes, but no skull
It provides insight into early vertebrate evolution.
What is Myllokunmingia?
Ear and ear capsule = skull, a true craniate
This organism is significant for understanding the early development of craniates.
What are myxini?
Hagfish, only surviving craniates
They have unique features such as a cartilaginous skull and the ability to produce slime.
What are the characteristics of myxini?
- Cartilaginous skull
- No jaws or vertebrae
- Segmented muscles and notochord for swimming
- Paired sensory capsules
- Produces slime to deter predation
- Can tie itself in knots
These adaptations help them evade predators.
What defines vertebrates?
Craniates with a backbone
Vertebrates are a subgroup within craniates, characterized by a vertebral column.
What is agnatha?
Jawless fish
This class includes species such as lampreys and hagfish.
What characterizes lampreys?
- Oldest living vertebrate lineage
- Cartilaginous skull and vertebrae
- Marine and freshwater
- Larvae = filter feeders, look like lancelets
- Adults = parasitic
Lampreys have a unique life cycle and feeding strategy.
Describe the life cycle of lampreys.
- Adult lampreys construct nests
- Fertilised eggs hatch in gravel
- Larvae drift downstream
- Larvae burrow and transform into parasites
- Adults feed on fish
- Ascend streams to spawn
This cycle shows their complex reproductive behavior.
What was the original composition of vertebrate skeletons?
Unmineralized cartilage
Cartilage serves as a flexible support structure before the evolution of bones.
