Biodiversity 5: Fish Flashcards
What were the ancient jawless fish called?
Ostracoderms ‘shell-skinned’
Describe the Ostracoderms
Dominated 450-375 mil years ago
Went extinct ~150 mil years ago, outcompeted by jawed fish
Heavily armoured
Covered with bony plates and scales surfaced in dentine and enamel (Protection)
Plates around mouth probably acted as a scoop for shovelling food into mouth
Early forms lacked pectoral fins = probably poor swimmers
Give 2 species that are modern jawless fish
Hagfish and Lampreys
Describe modern jawless fish
Eel-like
No armour
Skeleton cartilaginous
Protective slime production
Lack paired fins and jaws
Describe hagfish
Many are scavengers that feed on dead animals
Enter body through opening and eat from inside out
Only vertebrate that are isotonic with seawater
Describe lampreys
Predators/parasites of fish
Adults may be freshwater/marine
Larvae (ammocoetes) are eel shaped suspension feeders that live in send
Go through metamorphosis
Cartilaginous ‘vertebral column’
What are jawed vertebrates called?
Gnathostoma
Describe the Gnathostoma
Jaws
2 pairs of appendages = active roles
Developed into:
Fish: pectoral & pelvic fins
Mammals: Forelimbs & hindlimbs
Describe the evolution of jaws
Hinged to work up/down unlike invertebrates
Arose from modification of skeletal rods that support the pharyngeal slits
= Shows evolution as a remodelling process, rather than a creative one
What are ancient jawed fish called?
Placoderms ‘plate skinned’
Describe the placoderms
Silurian to the end of the Devonian period
All extinct
Large group of predators
Heavily armoured, some with cleaver like plates for biting prey
What are the two types of modern jawed fish called?
Cartilaginous Fish
Bony fish
What are the 2 groups of cartilaginous fish
sharks & rays
Ratfish & chimaeras
Describe the features of cartilaginous fish
- Flexible endoskeleton of cartilage (not bone!)
- Cartilaginous skeleton is a derived trait → new to that group (didn’t belong to an ancestor)
- Many are covered in small tooth-like placoid scales
- Some have acute senses adapted to predatory lifestyle
- Heterocercal tail (upper lobe bigger than lower lobe) and wing-like pectoral fins provide lift because body is negatively buoyant (heavy and no swim bladder)
Describe the acute senses some cartilaginous fish have evolved
Sharp vision, not colour
Nostrils with smell receptors
Lateral line system (row of microscopic organs) for detecting pressure changes
Electroreceptive organs in the head detect electric fields
Describe the tail and fins of cartilaginous fish
Heterocercal tail (upper lobe bigger than lower lobe) and wing-like pectoral fins provide lift because body is negatively buoyant (heavy and no swim bladder)
What is the endoskeleton of bony fish made from?
Calcium phosphate
What is the skin of bony fish like?
Flattened bony scales
What system do bony fish use to detect pressure changes?
Lateral line system
Describe the gas-sac organ in bony fish
→ either swim bladder or sometimes a lung
Hydrostatic organ for buoyancy
May act as an oxygen reservoir during periods of stagnation/ drought
= Don’t have to keep swimming to stay up in the water column
= Suggests bony fish derived from a murky freshwater ancestor
Describe the gills in bony fish
Gills covered by an operculum, with pharyngeal muscles
Acts like bellows to keep water flowing across gills (even while fish isn’t moving)
What type of fertilisation do most bony fish use?
External
What are the 3 classes of bony fish?
Lobe-finned fish
Lungfish
Ray-finned fish
What shape do all fish have? Describe it.
Fusiform means tapered at both ends
→ reduces drag for efficient movement in the water
(other marine organisms have convergently evolved this shape e.g penguins, seals, squid)
