Lecture 17 Flashcards
Protochordata, Craniata, Gnathostomata
All are within Phylum Chordata
- Protochordata
- Do not have a true brain, skull, or vertebral column
- Craniata (i.e. Vertebrata)
- Have a skull (cranium) and/or vertebral column
- Agnatha (Hagfish and Lampreys) only have a skull (no vertebrae)
- Gnathostomata
- Craniates with jaws
- Includes all of Craniata except for Agnatha
Phylogeny of fish!
fish itself is any non tetrapod vertebrate
Agnatha
Osteichthyes* (Bony Fishes)
Chondrichthyes
General characteristics to distinguish what is a fish (5)
- Form
- Locomotion in water
- Neutral buoyancy and the swim bladder
- Respiration
- Osmotic regulation
Form – types of scales for fish
- Placoid scales
- Ganoid scales
- Cycloid and Ctenoid scales
Placoid scales
- Small, conical, toothlike structures
- Typical of chondrichthyes
- Modified to teeth in sharks
Ganoid scales
- Diamond shaped
* Early bony fishes and living gars
Cycloid and Ctenoid scales
- Arranged in overlapping rows
* Typical of teleost fish
Locomotion in Water for fish
Movement achieved through undulation of the posterior end
• Generates thrust (forward motion) and lateral force (sideways motion)
• The lateral force causes fish head to “yaw”, or deviate in the same direction as the tail
• The “yaw” occurs more in more flexible fish
• A less flexible body plan is conducive to speed!!!!!!!!!!!!!!!
Buoyancy in fish
Swim bladder = gas-filled organ
Volume adjusted for neutral buoyancy
present in most pelagic (open sea) bony fishes
Not in very deep fish, and most bottom-dwellers
Why don’t Chondricthyes (e.g. sharks) have no swim bladder
- Asymmetrical tail provides lift,
* Large livers with squalene (particularly buoyant lipid)
Respiration for fish
Most fish use gills
• Breathe dissolved oxygen (oxygen that is in the water)
• Gills are located in the pharyngeal cavity
• Gills are covered with an operculum in bony fishes
• Increases efficiency of respiration
• Not present in sharks and rays
• Some fish also have lungs ,Capable of breathing air
Gills in fish
- Gill composed of thin filaments covered with an epidermal membrane
- The membrane is folded repeatedly into plate-like lamellae
- Enormous surface area
- Lamellae contain main blood capillaries
- Water is pumped continuously in the mouth, over the gills and out through the gill slits
- Gas exchange occurs across thin walls of blood capillaries
Osmotic Regulation in fish
- Maintenance of balance of fluids
- Freshwater and Marine fish have opposite challenges
- Freshwater fish are hyperosmotic regulators
- Marine fish are hypoosmotic regulators
Hyperosmotic Regulators
Freshwater fish
• Greater salt concentration in fish than in surrounding water
• Scales and mucous protect the fish, but water can enter across membranes (e.g. gills)
• Water pumped out by kidneys
• Salt-absorbing cells in the gill move salt from water to blood
Hypoosmotic Regulators
- Marine fish
- Contain a smaller concentration of salt than surrounding water
- Salt-secretory cells in the gill move salt out of body
- Salt is voided with feces or excreted by the kidney
Agnatha - Hagfishes caracteristics
- Jawless
- Entirely marine group
- Feed on annelids, molluscs, crustaceans, and dead or dying fishes
- Scavengers and predators (not parasitic)
- Poorly developed eyes
- Keenly developed sense of smell and touch
- Produce slime as a defence mechanism
Feeding and movement of hagfish
Agnatha
• Hagfish rasps bits of flesh from its prey
• Keratinized plates on tongue • Can itself into knot
• Passes the knot forward along its body until it is pressed securely against the side of its prey (for leverage)
Agnatha - Lamprey carcteristics
- Half are parasitic
* They use tooth-like plates of keratin for rasping a hole, through which fluids and tissues are sucked.
Chondrichthyes carcteristics
- Cartilaginous fishes (sharks, rays, chimaeras)
- Cartilaginous skeleton
- Bone entirely absent
- Placoid scales
- No swim bladder
Chondrichthyes species
Rays: skates, stingrays, electric rays, and manta rays
• Dorsoventrally flattened bodies
Chimaeras (also called ratfishes)
• Closest living relatives are sharks
• Instead of teeth their jaws bear large flat plates
Sharks
• Apex predators – most feed at the top of the
marine food chain
• Some exceptions: e.g. whale shark – largest extant fish species (up to 15 m) – is slow-moving and feeds on plankton
• Spined pigmy shark – 28 cm – feeds on small fishes
Sharks body plan
• Asymmetrical heterocercal tail
• Vertebral column turns upward and extends into the dorsal lobe of
the tale
• Provides lift as the shark swims
• Must constantly move to avoid sinking (even while sleeping!)
Osteichthyes
• Bony Fish
• Bone replaces cartilage
• 2 groups
• Ray-finned fishes & Lobe-finned fishes
• Gas-filled pouch branches from esophagus
• In fish that use these pouches primarily for gas exchange, they are
called lungs
• In fishes that use these pouches primarily for buoyancy, they are called swim bladders
Gills vs Lungs
- Which evolved first? Probably gills, but lungs also evolved early
- Ancestor of ray-finned and lobe-finned fishes had gills and lungs
In lobe-finned fishes (and tetrapods) lungs were preserved
• Modern lobe-finned fish also retained gills
• In ray-finned fishes, gills were preserved and lungs were adapted into swim bladder
Ray-finned fishes
- Symmetrical homocercal tail allows for greater speed
* Permitted by the swim bladder and improved control of buoyancy
Lobe-finned fishes
- Small group
- 6 species of lungfishes
- 2 species of coelacanths
- Ancestor of tetrapods is found within an extinct lineage of this group
- Lobe fins with a single bone that articulates with rest of body
- Diphycercal tails
- Lungs and gills
Lungfishes
- Can live out of water for extended periods of time
* E.g. African lungfishes live in streambeds during the dry season. They remain dormant until rain returns.
