Phylum Chordata

Question 1

What are the four characteristics of Phylum Chordata?

Answer 1

1. Bilateral symmetry
2. Deuterostomes –> triploblastic and radial, indeterminate cleavage
3. Has Coelom
4. Segmented body (i.e. spine) note: spine and vertebrate are different things

Question 2

What is the name of one of the the synapomorphies of chordates in the phylogeny?

Answer 2

Presence of a Notochord

Question 3

What two species fit into the chordate phylum?

Answer 3

1. cephalochordate

2. Urochordata

Question 4

What are the 4 synapomorphies (shared, derived characteristics) of phylum chordata?

Answer 4

1. Notochord (back cord)
   - cartilaginous skeletal structure that is like a flexible rod thats located along their back between the digestive tube and nerve cord
   - provides support and present in chordate embryos
   - IN VERTEBRATES: the notochord is reduced to disks between the vertebrae
2. Dorsal, Hollow nerve cord
   - only chordates have a holo DORSAL (from head to tail)
   - this develops from neural plate of ectoderm which rolls into a tube during embryonic development
   - nerve cord is present in spinal cord, nervous system and brain
3. Pharyngeal Clefts (gills)
   - located posterior to mouth and along digestive tract
   - connects the pharynx to external environment
   - allows water entering mouth to exit without entering the whole digestive tract
   - modified for gas exchange in vertebrates (become gill slits)
   - in terrestrial vertebrates, the pharyngeal clefts do not turn into slits, they turn into jaw support and parts of the ear
4. Muscular, post anal tail
   - contains muscles and skeletal elements
   - provides propulsive force in many swimming species
   - acts as a rudder, provides balance and grip
   - reduce in some species during embryonic development

Question 5

What are 2 non-synapomorphies of phylum chordata (traits that are 100% present in chordates but may or may not be present in other species before it)?

Answer 5

1. bilateral symmetry
2. segmentation (similar to arthropods, annelids, and chordates) and they are segmented using muscle blocks and vertebral column

Question 6

What are some characteristics of cephalocordata? and what species does it include?

Answer 6

• includes lancelets
• adult has all the chordate character states
• segmented –> serial arrangement of muscles and cephalization is minimal

Question 7

How do lancelets eat?

Answer 7

they are suspension feeders,
they wiggle into sand and suck in the water through their pharyngeal slits and water is sent out of their body via an atripore
- they have a mucous net that collects the food they eat

Question 8

What does the hox genes of lancelets tell us about the evolution of vertebrate brains?

Answer 8

• there are 3 hox genes present in the lancelet embryo that are also found in same order in the vertebrate embryo (controls development of vertebrate brain). This tells us that the vertebrate brain evolved from an ancestral structure similar to lancelet’s simple nerve cord

Question 9

what are some characteristics about the Urochordata and what species does it include?

Answer 9

• includes tunicates
• their larval stage includes all 4 synapomorphies and their adult stage does not look like chordates
• they go through metamorphosis to become adults and as adults, they don’t move (sessile) and filter/suspension feeders
• they don’t have a well defined head

Question 10

Why do we bother studying these creatures?

Answer 10

because their larval stage contains all synapomorphies of chordates which are important to study

Question 11

How do urochordata suspension feed?

Answer 11

using a pharyngeal basket (passes water through slits and water moves through mucous covered basket