12. Fish Diversity Flashcards
What are the characteristics of gnathostomes? 7
1. jaws present 2• paired appendages usually present 3•3 pairs of semi circular canals 4• notochord replaced by centra 5• endochondral bone 6• dentine-based teeth 7• no intermediate forms between jawed and jawless fish have ever been found
What are some features of the class Condrichthyes? 16
- Placoid scales
- Catrilagenous skeletons
- By the carbonifererous 60% of all fish were sharks
- Traditionally thought of as primitive because of their cartilaginous skeleton
- However, it turns out that many features are secondarily derived…
- No common ancestor between the holocephali & elasmobranchii has been found
its a shame cartilage doesn’t fossilise
7• 850 living sp, generally large
8• calcified skeleton, rarely ossified
9• skull lack sutures
10•have teeth derived from placoid scales
11• 5, 6 or 7 external gill slits - Few fossils - only have teeth
13/ incl. hammerhead sharks, bull shark, angel shark - subclass elasmobranchii (sharks skates & rays)
- no sulca plates in skull so hard to age them, and more gill slits = more ancient
- Often well adapted, apex predators
Describe the sensory ability of the condrichthyes. 5
- mechanoreceptors- sense low frequency
vibrations - Pores are full of jelly, vibrate, triggering nerve cells, signal goes to brain
- long distance special receptor organs –
neuromast cells - closer range – switch to vision
5 final stage – ampullae of Lorenzini sense
bioelectric fields
Describe shark skates (subclass elasmobranchii). 4
- two lobed pelvic fin
2• stocky tail, no spine
3• 2 dorsal fins on tail
4• scales
Describe rays (subclass elasmobranchii). 4
1• one lobed pelvic fin
2• slender tail, stinging spine
3• no dorsal fin on tail
4• no scales
Describe the common characteristics of elasmobranchii. 3
1• carPlaginous – liYle or no fossil record
2• lots of teeth found though & the odd scale
3• all extant species known by upper cretaceous (100mya) to the paleocene (50mya)
Describe the chimeeras/holocephali (subclass of condrichthyes) 6
- diverged from sharks ~360mya
2• 31 extant sp.
3• jaws have large flat plates - adapted to crush food
4• upper jaw fused to cranium
5• mixed diet – cructaceans, fish, seaweed - Include spookfish and ratfish
Describe the physiological characteristics of the condrichthyes. 10
- Body fusiform
- Ventral mouth
- Placoid scales on skin
- Endoskeleton entirely cartilaginous
- J-shaped stomach
- 5-7 pairs of gills, no swim bladder or lung
- Slightly hyper-osmotic to sea water
- 3 pairs of semi circular canals
- Good sense of smell, lateral line, electroreception
- separate sexes, internal fertilisation
Describe the acanthodians, a subclass of the class teleostomi. 9
1.Includes the oldest known gnathostome from the Late Ordovician. 2• Pectoral and pelvic fins have been modified to long spines 3• Slender bodied - may have been fast 4• One or two dorsal fins. 5• Heterocercal tail. 6• Up to six pairs of belly spines. 7• Body covered scales. 8• Most lack teeth - lost secondarily 9• Large eyes
Describe the actinopteryngii, a subclass of the superclass osteichtyes.9
First known from the Mid Devonian in Scotland Cheirolepis
2• Slender scaled body
3• Heterocercal tail
4• Large triangular dorsal and anal fins
5• Paired pectoral and pelvic fins
6• Articulated tail scales
7• Large skull, bony braincase made from dermal bone plates
8. More common than other subclass, sarcopterygii.
9. oseichtyes are most common fish in sea
10. actinoperyngii are ray finned
Describe palaeonisciformes/primitive actinopteryngii. 4
1• heterocercal tail
2• ganoid scales
3• bichir has lungs
4. incl saddle bichir and pallid sturgeon
Describe neopterygians. 4
- Fish that evolved after palaeoniscifromes, part of actinopteryngii.
- early ones include bowfin and gar
- Bowfin:
• long dorsal fin
• bony plate between lower jaws
• gulp air - Gar:
• large ambush predators
• elongated bodies
• needle-like teeth
• gulp air
Describe the morphological characteristics of actinopteryngii. 7
- Skeleton with endochondral bone,
- Ganoid scale in ancestral, cycloid, ctenoid or absent in advanced forms
- Paired & median fins
- Jaws, teeth usually present
- Gill respiraPon primarily (some lungs)
- Swimbladder present
- Heart with undivided atrium & ventricle
Describe sarcopterygii/lobe-finned fish. 10
- Skeleton with endochondral bone,
- Embedded dermal scales
- Paired and median fins
- Jaws present, teeth covered in true enamel, crushing plates
- Gill, lungs & skin respiration
- Vascularised swim bladder
- Heart with separate atria, partly divided ventricle
8 muscular lobed paired fins with bony skeletons
9 lungfishes possess diagnostic grinding/crushing tooth plates
10 tri-modal breathers (lung, skin gill)
How do some specialised sarcopterygii breathe? 5
- Lungfish have lungs
- As water levels drop, borrow into ground and cover selves with mucus
- go into torpor - blood pressure and heart rate drop
- survive the dry season like this
- Usually use gills in aquatic environment and lungs in torpor
