Chordates Flashcards
Summary
5 key features of the Chordates
- Notochord,
- dorsal hollow nerve cord,
- pharyngeal slits,
- endostyle,
- post anal tail
Chordates are Deuterostomes [all previous to this protostomes]
4 points
- Triploblastic
- Radial cleavage
- Mesoderm comes from archenteron (=enterocoely)
- Blastopore becomes anus
classification
Phylum: chordates
Definition of chordates
- Deuterostomes that have, for at least part of their life cycle:
A notochord (L. chorda = “string”)
A hollow dorsal nerve cord
Pharyngeal slits
An endostyle
A post-anal tail
Notochord [important in function]
6 points
- A flexible rod of glycoproteins encased in actin
- Mesoderm origin
- Muscle attachment
- Precursor of vertebrae
In most vertebrates it becomes part of the intervertebral disc - Signalling during development
- Can be found in:
Cephalochordates, larvae of tunicates
Hagfish, lampreys
African lungfish, coelocanth, sturgeons, tadpoles
Hollow Dorsal Nerve Cord
- Forms from the ectoderm
2. In non-chordates, the nerve cord is solid and ventral
Pharyngeal Slits
- Openings in pharynx
Allow water to flow in via the mouth and out of the pharynx
Filter feeding
Retained as gill slits in jawless fish (7) cartilaginous fish (5, occasionally 6-7) bony fish (1)
2. Pharyngeal arches become, in vertebrates: Jaw bone(s)
Hyoid bone
In fish: brachial skeleton (supports gills) and/or pharyngeal jaws
In tetrapods: parts of ear, tonsils, thymus
Endostyle
3 points
- Organ within the pharynx
Present in cephalochordates, tunicates, larval lampreys; assists in filter feeding - Secretes mucus
Food particles adhere to mucus
Cilia sweep mucus through pharynx into oesophagus - Adapted into thyroid gland
Post-anal tail
4 points
- Has muscular (and skeletal) components
- Notochord and nerve cord extend into the tail
- Evolved for propulsion in water
- In non-chordates the digestive system runs the full length of the body.
Respiration & Circulation
2 points
- The primitive chordate respires through diffusion across skin
Pharyngeal slits devoted to feeding not oxygen exchange
- Basic circulation of blood
Dorsal system of vessels run from head to tail, paired aortae in front half
Ventral vessels run from tail to head via the liver
Nervous system
- Dorsal nerve cord protected by the notochord
- Slight enlargement at anterior end forms brain
- Visual sense organs located in neural tube
Frontal eye
Joseph cells in dorsal part
Hesse organs in ventral part - Oral cirri have sensory cells
Digestion and Excretion
4 points
- Gather plankton into pharynx
- Attaches to mucus produced by endostyle
Cilia push mucus over pharyngeal arches
Once laden with food, mucus pushed into digestive tract
- Water passes through pharyngeal slits into atrium and then out via the atriopore / gonopore
- The liver is a blind-ending caecum that branches from the gut
Cell lining engulfs food particules
Other Systems
Excretion
4 points
- Segmented ‘kidneys’ have protonephridia
- More like the invertebrate system
- Blind-ended
- Osmoregulation through partial pressurisation
Other Systems
Reproduction
4 points
- Segmented gonads
- Spawn once a year
- External fertilisation
- Larvae are planktonic
Phylum Chordata
3 points
- May be a very old phylum (c. 505 Mya) during the Cambrian explosion
- Subphylum: Cephalochordata
- Olfactores
Subphylum Tunicata
Subphylum Vertebrata
Cephalochordata (subphylum)
3 points
- Notochord extends into head
- Lancelet or amphioxus (AGr amphi = “on both sides” + oxus = “pointed, sharp”)
- Spend most of time half-buried in sand, filter feeding
Tunicata
(subphylum)
5 points
- Well-developed heart and circulatory system
- Carries oxygen and nutrients dissolved in plasma
- Hollow cerebral ganglion and neural gland
- Produce cellulose for various functions
- Suspension feeders, employing endostyle and pharynx
Vertebrata
subphylum
- L. vertebra = “(spine) joint”
- Also called “Craniata” (L. cranium = “skull”)
- Hagfish do not have vertebrae
Agnatha
3 points
- Formerly, the living members were put into two classes:
Myxini (hagfishes)
Hyperoartia (lampreys)
- Now recognised as single monophyletic group called Cyclostomata
- Well-represented in fossil record by other classes such as conodonts and ostracoderms
Agnatha
Bodyplan
4 points
- No jaws
- No paired fins or other limbs (in modern forms)
- Notochord in both larvae and adults
- Seven or more paired gill pouches
Agnatha
Respiration
- Water taken and out of pharynx through gill pores
Agnatha
Circulation
4 points
- Two-chambered heart
Only has deoxygenated blood - Aorta branches into two to serve gills
- Accessory pumps
- Blood returns to heart via veins
Agnatha
Digestion
4 points
- No definable stomach
- Pharynx subdivided by valve
- Prevents food entering the respiratory system
- Can eat and breathe at same time
Agnatha
excretion
4 points
- Paired kidneys
- Two ureters open into urogenital sinus
- Maintain osmotic neutrality with environment
- Regulation of ions rather than water
Agnatha
Nervous system
4 points
- Brain and nerve cord
- 10 pairs of cranial nerves
- Spinal nerves
- Autonomic nervous system
Agnatha
senses
6 points
- Olfactory sac
Single nostril, does not connect to respiratory system - Eyes
- Pineal apparatus (‘eye’) [3rd eye]
- Integumentary photoreceptors
- Ears
- Lateral line
Agnatha
Reproduction
5 points
- External fertilisation
- Believed to only breed once in their lives
- Most species of hagfish are hermaphrodites
- Larvae of lampreys = ammocoetes
Filter feeders
Closely resemble
cephalochordates in this form
Undergo metamorphosis
- Hagfish don’t have larval stage
Agnatha
Ecology : Lampreys
- Coastal / freshwater
- Many species migrate to freshwater to mate
- Feed on live prey
Mostly blood, inject anticoagulants
Agnatha
Ecology : Hagfish
4 points
- Marine
- Mostly scavengers
- Tie themselves into knots to lever scraps of food off carcasses
- Can produce copious amounts of slime
Expands in water – one hagfish can produce 20 litres
Tunicata
Ascidiacea (Sea squirts)
4 points
- Sessile, solitary or colonial
- Filter feeders
Water enters through oral siphon, through pharynx, and out through cloacal siphon - No excretory or respiratory organs
- Tunic
Secreted by epithelial cells
Often pigmented
Tunicata
Appendicularia (salps)
[barrel shaped planktonic tunicate]
6 points
- Common planktonic organisms, mostly transparent
- U-shaped body with trunk and elongated tail
- Trunk has all organs and a midventral anus
- Tail contains notochord, nerve cord, and 2 muscle bands
- Protoandrous (“male-first”) hermaphrodites
- House
Secreted by epithelial glands
Simple temporary structures or more complex in form
