Fishes: Chondrichthyes Flashcards
Gnathostomes (jawed verts) main features
- Duplication of hox gene complex (4 hox gene clusters)
- 2 olfactory bulbs
- Centrum
- Properly formed vertebrate
Placoderms
- Extinct species
- Name means plate skin - covered in plates
- Variety of body forms and sizes >8m
- Marine and freshwater
- Teeth but not replaced
Placoderm reproduction
- Viviparity - gave birth to live young (embryos found in female bodies - fossils)
- Internal fertilisation - claspers behind pelvic fin.
- Clasper found in scottish fossil - first evidence of copulation (385 mya)
Acanthodians (spiny sharks)
- Stem/basal chondrichthyans (cartilaginous fish)
- Extinct
- Toothless or tooth whorl (also seen in cartilaginous fish)
- Mainly marine, also freshwater
Placoderm heart
- Gogo fossil - two chambered heart, heart is getting more complex
Chondrichthyes?
Cartilaginous fish
Chondrichthyes - cartilaginous fish
- 400 mya
- Mineralised cartilage - allows for buoyancy and flexibility
- Most have hyostylic jaw suspension.
- Internal fertilisation
How do chondrichthyes maintain buoyancy?
- lipid-filled liver aids buoyancy - benthic shark would have low lipid levels, active sharks would have more lipid for more buoyancy.
- High blood urea concentration - also aids buoyancy
- Mineralised cartilage aids buoyancy
Hyostylic jaw suspension
Chondrichthyes
- Held in place at the back by the hyomandibular arch and by ligaments at the front.
- Jaw has independence from the skull
- Jaw held together with ligaments
- Able to drop upper jaw down and protrude it forward
- Allows jaw flexibility
2 groups of Chondrichthyes
- Holocephalans
- Elasmobranchs
Holocephalans
Chondrichthyes
- Ratfish
- Rabbit fish
- Chimaera
Elasmobranchs
Chondrichthyes
- Sharks
- Skates
- Rays
Holocephalans structure
- Holostylic jaw (upper jaw fused to the skull)
- Have large pectoral fins
- Whip like tail
- 4 gill slits
- Tooth plates - crushing
- Mechanoreceptors and electroreceptors
- Have a spine that can produce venom on dorsal fin
Holocephalans reproduction
- Oviparous (lay eggs after internal fertilisation)
- Males have head clasper - used as an attachment device in mating
- Modified pelvic fin with clasper
Sharks are further divided into?
Chondrichthyes - Elasmobranchs
- Galeomorphs (anal fin)
- Squalomorphs (no anal fin)
Galeomorphs (anal fin) examples
Chondrichthyes - Elasmobranchs - sharks
- Great whites, hammer heads, whale sharks, thresher shark
- Large active predators
- Whale shark - not predator (filter feeder)
Squalomorphs
Chondrichthyes - Elasmobranchs - sharks
- Smaller
- No anal fin
- E.g. spiny dogfish
Batoidea features
Elasmobranchs - Batoidea - skates and rays
- Dorso-ventrally compressed
- Have a spiracle in dorsal side
- Mouth and gills slits on ventral side
- Water drawn in through gills slits and out through mouth and gills (how they feed.
- Many are benthic
- Manta ray is a filter feeder using cephalic fins to direct water in through mouth
- Jaw is protrusible, teeth are flat plates (sexual dimorphism - teeth become sharp (for latching) depending on reproductive season.)
- Some produce electric currents (predation and communication)
Shark examples: Cookie cutter shark
Small but takes many bite chunks out of prey
Examples of sharks: Hammerhead
Theories for the use of the hammerhead. Improve sensitivity of receptors? Binocular vision (accurate perception of depth, distance)? ← binocular vision newest theory
Cartilaginous fish
- Teeth
- Liver (25% body mass)
- Paired fins
- Short intestine with high surface area
- Spiral valve in intestine
- Tail is heterocercal - asymmetrical - gives them lift when swimming
What are Batoidea
Skates and Rays
Placoid scales
Chondrichthyes
- Denticles (tooth-like structures found on surface of skin)
- Sharks
- Shape and arrangement is species specific
- Allow for a smoother flow of water of the skin
- Pulp cavity - Dentine middle - Enameloid outer layer.
How are placoid scales modified in skates and rays?
- Single placoid scale modified to barb in sting rays.
- Many small placoid scales along dorsal line of skates (reduced into small nobbly protrusions)
How do dog fish embryos use their placoid scales?
Use them to tear and manipulate food by rubbing the food across their back in the opposite direction of the scales
Skates and Ray reproduction
- ray (viviparous)
- Skate (oviparous)
How to electric rays stun their prey?
Use electrical currents of around 200v to stun prey
Diversity in Ray feeding behaviours
- Manta rays are filter feeders
- Electric ray kills prey
What is the name of Chondrichthyes Teeth structure?
Tooth Whorl
Where in the jaw does the tooth whorl sit?
Teeth form within skin - tooth whorl rests on jaw
What is the condrichthyes tooth whorl ?
Teeth are continuously being replaced (in a conveyer belt fashion)
Condrichthyes Tooth whorl shapes
- Shapes vary depending on species
- Shapes and size vary depending on where they are in the mouth
- Different shapes maximise damage to prey
Some chondrichthyes kill mammal prey by exsanguination, what does this mean?
- Cause max damage and blood loss to the mammal
- Weaken prey so they can feed on it (bleed to death)
How did Megaladon feeding habits effect baleen whale size?
It has been suggested that megaladons would would feed on baleen whales and keep their size reduced. Acting as a cap
How do chondrichthyes detect their prey?
Chondrichthyes sensory systems
- Mechanoreceptors: detect vibrations
- Chemoreceptors: Acute sense of smell
- Electroreceptors: detect electrical pulses of prey
- Visual: allow site in low light
Mechanoreceptors
Chondrichthyes sensory systems
- Neuromast organs
- Detect vibrations from prey in the water
- Found along lateral line
Chemoreceptors
Chondrichthyes sensory systems
- Olfactory organs
- acute sense of smell
- They will turn to the side (nostril) that detects the cue first and follow that direction.
Electroreceptors
Chondrichthyes sensory systems
- Ampullary organs
- Organs found in the head of sharks
- Found in pectoral fins of rays
- Found on the Rostrum of holocephalans
- Electrical charges going round preys body will be detected by these organs
Vision
Chondrichthyes sensory systems
- Well developed eyes for low light intensities
- Rod rich retina: Cells with crystals of guanine behind retina.
- Shines light off retina (almost like a wall of mirrors behind eye)
- Tapetum lucidum
What is tapetum lucidum?
- Rod rich retina
- Cells with crystals of guanine behind retina
- allows good vision in low light
What is the sequence of events in predation of chondrichthyes?
- Olfaction or mechanoreception
- Vision - prey detection
- Attack - electroreception (eyelids cover eyes for protection - rely soley on electroreception as can’t see).
What is different about brain size and itelligence of chondrichthyes
- Brain size is proportionally heavier than brains of other fishes
- Similar brain to body mass ratios to some tetrapods
- Manta rays have shown mirror self recognition (some debate over this).
What are pelvic claspers and what are they used for?
Chondrichthyes reproduciton
- Pelvic claspers (associated with pelvic fins)
- Aids in internal fertilisation.
- Claspers have hooks and other attachment devices that ensure claspers stay in place
- A way of maintainting attachment to female during reproduction
How is sperm released?
Chondrichthyes reproduciton
Via siphon sacs
what are some male adaptations for maintaining attachment to the female during mating
Chondrichthyes reproduciton
- Males bite onto females
- In some smaller species the male wraps arounf the female
- Some ray species get sharper teeth during maring season to latch onto female
How have females adapted to males biting them during copulation?
Females have thickened skin in areas where males latch on.
Different Breeding systems within chondrichthyes
Oviparous
- Oviparous (egg laying).
- Water can flow through egg cases (respiration).
- Egg case contain tentril that attach to rocks etc. (e.g. mermaid purse)
- Nutrients from yolk
Different breeding systems within chondrichthyes
Ovoviviparity
- Ovoviviparity - retain eggs in oviduct until hatching (lecithotrophy).
- Give birth to live young.
- Nutrients from egg yolk.
Different breeding systems within chondrichyes
Viviparity
- Vivipary - nutrition comes from yolk and female (matrotrophy).
- Some females secrete substances (uterine fluid).
- Some ovulate to feed young or cannibalism (embryos eat each other (survival of the fittest).
- Some have yolk sac placenta (placentotrophic viviparity)
- Once born no parental care.
Why are chondrichthyes threatened and why is this a conservation issue?
- Long gestation period and long lived means generational development is slow
- Invest a lot in reproduction and takes many years to reach sexual maturity.
- Don’t reproduce every year.
- Apex predators - consequences for the food chain if they decline
What is a hunting adaptation of great white sharks?
Approach prey with sun behind them so the prey cant see them
Greenland shark life and sexual maturity
Thought to live for 400 years and reach sexual maturity at 150 years old
