Chordates and Early Vertebrates

Question 1

Chordata

Answer 1

Bilateral symmetry
Possess a coelom
Deuterostome development:
1. Radial, indeterminate cleavage.
2. Enterocoelus coelom development
Metamerism
Cephalization

Question 2

Deuterostomia

Answer 2

Chordata (cephalochordates, tunicates, vertebrates)
Hemichordata (acorn worms, pterobranchs, extinct graptolites)
Echinodermata (sea stars, urchins, crinoids)

Question 3

Graptolites

Answer 3

Extinct class of colonial pterobranch hemichordates.
Sessile and planktonic colonies like tiny sawblades
Early-mid Paleozoic (mainly ordovician and silurian) 540-320 mya.
Graptolite species were generally widespread and short-livved, valuable fossils for correlating strata.

Question 4

Echinoderms

Answer 4

Evolved from bilaterally symmetrical ancestors.

Question 5

Ancestral deuterostomes

Answer 5

Bilaterally symmetrical.
Deuterostomic development
Not much else known

Question 6

Characteristics of chordate body plan

Answer 6

Dorsal hollow nerve chord
notochord
pharyngeal slits (gill slits)
Segmented muscle blocks
Post anal tail

Question 7

Cephalochordates

Answer 7

They have a much more vertebrate-like body plan than urochordates.
Their fossils show a conserved body plan.
Similarites in outward morphology support cephalochordates being more closely related to vertebrates.

Question 8

Tunicates

Answer 8

Highly derived body plan.
Kowalevsky 1856 realised they were chordates by allying the adult with the larva.
Larvae have chordate characteristics:
- notochord, dorsal nerve cord, muscle cells
- post anal tail, gill slits.
Body plan changes during metamorphosis.
Larvaceans appear to display a larval body plan throughout their lives.
Molecular phylogenetic data support tunicates as sister group to vertebrates.

Question 9

Placodes

Answer 9

Cranial placodes give rise to sensory organs during development.
Placodes thought to be unique to vertebrates.
Genes involved in placode development are expressed in distinct territories in tunicates.

Question 10

Vertebrate

Answer 10

Backbone
52,000 species of vertebrates

Question 11

Craniata

Answer 11

Chordates that have a head
Origin of a head opened a completely new way of feeding for chordates, active predation.
Skull, brain, eyes and other senses.

Question 12

Vertebrate endoskeleton

Answer 12

Made of cartilage or bone
All have a cranium to protect the brain
Almost all have vertebrate to protect the spinal cord.
Important for muscle attachment.

Question 13

Agnathans

Answer 13

Jawless vertebrates
Earliest vertebrates
Hagfish have secondary lost vertebrae

Question 14

Extinct groups of early vertebrates

Answer 14

Agnathans: jawless
Gnathostomes: jawed
Placoderms: small/gigantic gnathostomes
Acanthodians: spiny sharks, devonion gnathostomes, ancestors of cartilaginous and bony fish.
Cartilaginous fish (chondrichthyans): Chimaeras, sharks and rays. devonian to present.
Bony fish (osteichthyans): gnathostomes with lungs or swim bladder. ray finned and lobe finned fishes. devionian to present