vertebrates : reign of the chondrichthyans Flashcards
1
Q
class : Chondrichthyes
A
- 970 living species
- defining features:
- prismatic calcification of endoskeletal cartilage
- pelvic claspers
- specialized as marine predators
- dominated ancient seas
2
Q
subclass : elasmobranchii
A
- 5-7 gill opening
- dermal, placoid scales
- replacement dentition (derived from placoid scales)
- upper jaw not fused to cranium
- ribs
- spiracle
- several radiation, all extinct except division = neoselachii
3
Q
Division Neoselachi
A
- overhanging mouth - several jaw modifications
- calcified vertebral centra replace unconstricted notochord
- basal fin supports : fused, flexible, horny rays support fin
- developed sexual dimorphism and internal fertilisation
- electroreception
- oil accumulation (buoyancy)
- 2 subdivisions :
- selachii (sharks: 8 orders, 403 spp)
- Batoidea (rays: 5 orders, 534 spp)
4
Q
Order Carcharhiniformes (requiem sharks)
A
- 244 spp
- tropical & subtropical
- nearshore
5
Q
Order Lamniformes (Mackerel sharks)
A
- 15 spp
- offshore, pelagic
e.g. Mako, White, Thresher, Basking
6
Q
Order Squaliformes (dogfish sharks)
A
- 97 spp
- successful in North Atlantic, North Pacific & deep sea
7
Q
Rajiformes (skates)
A
- 285 spp
- deep water
- high latitude
- 2 dorsal fins
- long slender claspers
- dorsally depressed
8
Q
Myliobatiformes (stingrays, eagle rays)
A
- 183 spp
- inshore
- tropical
- 0 dorsal fins, tail spine
- short, stout, cylindrical claspers
- dorsally depressed
9
Q
Chondrichthyans : body size
A
relatively large
- smallest (17cm) : Etmopterus perryi
- largest (>12m) : Rhincodon typus
10
Q
Chondrichthyans : habitats
A
- shallow temperate and tropical waters
- mainly coastal marine
- 5% of species in open water
- 5% of species in freshwater
- shallow waters, seldom > 3000m
- generally outside environmental extremes
11
Q
Movement and buoyancy in sharks
A
- anguilliform or rajiform swimming
- efficiencies through :
- integument
- fins
- swimming type
- efficient buoyancy devices :
- no gas bladder
- lightweight skeleton
- oil-filled liver
- heterocercal tail -> creates lift
- pectoral adjust pitch
12
Q
Chondrichthyans : movement and home ranges
A
- highly mobile, often large home ranges
- home range increases with age
- different movement patterns :
- local
- coastal
- oceanic
13
Q
Chondrichthyans : metabolism and growth rate
A
- low metabolic rates
- low aerobic scope
- low food requirements
- variation among species depends on activity
- slow growth, long life spans
14
Q
Chondrichthyans ; feeding habits
A
- almost all carnivorous, many apex predators:
- live prey
- scavengers
- planktivorous
- often nocturnal feeders
- strong bite, underslung jaw
- teeth for piercing, slicing, crushing
- dentition replacements
- other feeding features :
- tailfin (thresher sharks: herding & stunning
- ‘saws’ (sawsharks: slashing)
- electricity (torpedo rays : stunning)
- cephalic horns ( manta rays : guiding )
- suction in some species
- from enlarging orobranchial cavity
- protrusion of palatoquadrate
- improves bite speed and strength
15
Q
Chondrichthyans : sensory physiology
A
often nocturnal : rely on non-visual senses
- high olfactory sensitivity
- good vision (esp at night)
- mechanoreception
- acoustic sensitivity
- electroreception
- large brain : integration
