- Development of the vertebrate jaw in the Silurian Period
- Chondrichthyes and Osteichthyes do not share many common features
- Chondrichthyes (cartilaginous fish) are the sharks, rays, and dogfish
- Osteichthyes (bony fish) have two main groups
Sarcopterygii – lobe-finned fish
Actinopterygii – ray-finned fish
Of which the Teleosti contains 96% of all species
..
summary
Development of the vertebrate jaw in the
Silurian Period
summary
Chondrichthyes and Osteichthyes do not share many
common features
summary
Chondrichthyes (cartilaginous fish) are the
sharks, rays, and dogfish
summary
Osteichthyes (bony fish) have two main groups
- Sarcopterygii – lobe-finned fish
- Actinopterygii – ray-finned fish
Of which the Teleosti contains 96% of all species
What is a fish ?
2 points
- A gnathostome vertebrate
Vertebrata divided into the Agnatha (jawless) and the Gnathostomata (jaw-mouths)
- Gnathostomata
2 lineages
Chondrichthyes
Osteichthyes
tetrapods and bonyfish (Osteichthyes)
2 points
- tetrapods shared common ancestor with bony fish
- Tetrapods are therefore a member of the clade that contains the bony fish
i. e. we are all fish
Gnathostoma
2 points / divisions
- Chondrichthyes
(AGr khondros = “cartilage” + ikhthus = “fish”) - Osteichthyes
(AGr osteon= “bone” + ikhthus = “fish”)
Actinopterygii
(AGr. aktis = “ray” + pterux = “fin”)
Sarcopterygii
(AGr. sarx = “flesh” + pterux = “fin”)
vertebrate jaw evolution
4 points
- Vertebrate jaw probably evolved in the Silurian Period (444-419 Mya)
- Driven by respiration efficiency rather than feeding
- Jaw and hyoid developed from the first two pharyngeal arches
- “Age of Fishes” – Devonian (419-359 Mya)1.
Body plan
Chondrichthyes vs Osteichthyes
- Position of mouth
- Body shape
- Exoskeleton
- Endoskeleton
- Caudal fin
- Pelvic fins
- Ventral
Anterior - Usually dorso-ventrally flattened
- Usually laterally flattened
Dermal corset, separate placoid scales
Overlapping dermal scales - Cartilaginous
Mostly bony - Heterocercal
Homocercal or diphycercal - Usually posterior
Mostly anterior
Respiration and Circulation
Chondrichthyes
5 points
- 5 pairs of gill slits
- First gill slit usually adapted into a spiracle behind eye
- Plate-like gills separated by septa (“walls”)
- may have gill rakers
- Ram ventilation – swim with mouth open
Respiration and Circulation
Osteichthyes
3 points
- 5 pairs of gill slits protected by an operculum
- Hair-like gills
- Water pumped over gills
Two phase action, buccal and opercular
Thermoregulation
Chondrichthyes
5 points
- Most are poikilothermic
- Behavioural thermoregulation
- Homoeothermy found in mackerel sharks and allies
White shark, mako shark - Raise temperature in brain and eye
- Better vision
Thermoregulation
Osteichthyes
7 points
- Most are poikilothermic
- Some can maintain muscles at higher than environmental temperature
- Fast-swimming fish
- Polar fish
- Raise temperature in brain and eye
- Better vision
- Marlin and swordfish
Digestion and Excretion
Chondrichthyes
4 points
- Mouth ventral to head
- J-shaped stomach
- Short intestine with spiral valve
- Common urinogenital aperture leads to a cloaca
Digestion and Excretion
Osteichthyes
4 points
- Mouth anterior to head
- Variable shaped-stomach
- Long intestine without valve
- Separate anus, urinary and genital apertures
Nervous system and senses
Chondrichthyes
4 points
- Brain
large olfactory lobes and cerebrum
Small optic lobes and cerebellum - Monochromatic vision
- Naturally far-sighted
- Ampullae of Lorenzini
electroreceptors
Nervous system and senses
Osteichthyes
7 points
- Brain
small olfactory lobes and cerebrum
large optic lobes and cerebellum - Colour vision
- Naturally near-sighted
- Chemoreception
- Lateral line
- Currents and vibrations
- Auditory senses via swim bladder
Reproduction
Chondrichthyes
- Ovoviviparous and oviparous
Egg cases - Internal fertilisation
Males have pelvic fins adapted into claspers for sperm transfer - Dioecious
Reproduction
Osteichthyes
5 points
- Most are oviparous
- External fertilisation
- Dioecious
- Simultaneous hermaphroditism
Deep sea fish - Sequential hermaphroditism
Protandry (male first)
Protogyny (female first) is more common
Buoyancy
Chondrichthyes
- Rely on fatty liver to give neutral buoyancy
Up to 25% of body weight
Buoyancy
Osteichthyes
2 points
- Bodies are denser than water
- Swim bladder
Absent in fast-swimming fishes
Open in some fish, acting like a lung
Closed in most – gas exchange via a net of blood vesses
Locomotion
3 point
1. Anguilliform Move most of the post-head body 2. Carangiform Move about half the body 3. Ostraciiform Inflexible body, move just tail
Osteichthyes
Actinopterygii: Ray-finned fish (Teleostei)
- Moveable premaxilla – can protrude jaws
- Homocercal tail with equal-sized lobes
- Tend to be lighter and more flexible than more basal fish
