Lec 6/7 Part c Flashcards
Cyclostomata
Jawless fish
Petromyzontiforms
‘Stone sucker’
Slender scaleless up to 1m long
Anguilliform swimmer
Several species in Canadian waters
Sea lamprey
An invasive pest in the Great Lakes
Petromyzontiforms species
40 extant species in two genera: Petromyzon and Lampetra
Petromyzontiformes inhabit
Temperate fresh or salt waters, mostly northern hemisphere
Petromyzontiformes diagnostic features
Absence of paired fins
Seven pairs of gill pouches
Single median nostril (lead into blind olfactory pouch)
Adenohypophysis and pineal eye
Well developed eye
Presence of a velum in the pharynx
Keratinized “teeth” on the tongue
Piston cartilage to support the tongue
Petromyzontiformes feeding behaviors of larvae
Ammocoetes are amphioxus-like filter feeders
Petromyzontiformes adult feeding behavior
Have a non-feeding adult stage
About half of all species are parasitic drinking blood of other fish
Petromyzontiformes respiration
Flow through ventilation
Tidal style ventilation in adults during parasitic feeding or when mouth attached to stones
Flow through ventilation
Water drawn into mouth and pumped out through seven gill openings
Tidal style ventilation
Water drawn in and out through seven gill openings
Osmoregulation
Gill and kidney regulate concentrations of ions, water, nitrogenous wastes, and overall balance of the body fluid, as in jawed fishes
Petromyzontiformes reproductive migration
Anadromy- Adults live in oceans then migrate to freshwater rivers to breed
Petromyzontiformes fossil lampreys earliest record comes from
The Late Devonian
Myxiniformes
Slender, scaleless, pink in color
0.5 M long
Anguilliform swimmer
Difficult to breed in captivity
Many aspects are yet to explore
Huge gap of fossil lampreys record until
The Early Cretaceous
Growth series found for fossil lamprey known as
Proscomyzon
Myxiniformes species
75 extant species in two genera- Eptatretus and myxine
Number of gill pouch varies between species, up to 15
All known species are deep ocean dwellers, mostly near the sea floor
Found worldwide except in polar regions
Myxiniformes diagnostic features
Absence of paired fin
Absence of image forming eye
Single median nostril connected to pharynx
Three pairs of barbels as chemosensory organs
Presence of a velum in the pharynx
Tongue with keratinized “teeth”
90-200 pores for slime glands along both sides of the body
Myxiniformes: Slime
3-4 % of the hagfish’s body mass
Long proteinaceous threads that uncoil to form a network of intertangled protein strings. Water slowly passes through the string network
Can be released actively and passively
Primarily if not exclusively used for defense
Myxiniformes feeding behavior
Rely exclusively on olfactory cues
Scavenger and predator
Myxiniformes- Knotting
Hagfishes twist themselves into knots for
Predation: Increased pulling force when tearing fresh from carcasses/prey
Escape when seized by predators
Clean themselves of their own slimes
Myxiniformes reproduction
Female to male ratio is ~100-1
Some species are hermaphroditic
Eggs are anchored to seafloor by hooks
Absence of a larval stage
Hermaphroditic
Same individual carries gonads of both sexes
Myxiniformes respiration
Flow-through ventilation
Mouth may contribute to ventilation during swimming
Flow-through ventilation
Water is drawn into nostril and pumped out through seven gill openings
Myxiniformes
Osmoregulation
Low metabolic rate contributing to feeding in a hypoxic condition during scavenging
Isosmotic
Organs such as kidney still regulate ionic balance
Slime glands may help with controlling ionic balance
Isosmotic
Body fluids having the same osmotic pressure as seawater
Myxiniformes- fossil hagfish earliest record
Later Carboniferous
Myxiniformes- fossil hagfish huge gap in fossil record until
Cretaceous
Shared diagnostic features of petromyzontiforms and myxiniforms
A single median nostril
Gill arches lack joint
Presence of velum in the pharynx
A tongue with keratinized teeth
Two semi-circular canals in the inner ear
Phylogenetic hypotheses of similarities petromyzontiforms and myxiniforms
Craniate theory
Hagfish as an outgroup
Absence of true vertebrae in hagfish
Development of neural crest differ in hagfish
Phylogenetic hypotheses of similarities petromyzontiforms and myxiniforms
Cyclostome theory
Hagfish and lamprey as a monophyletic group
Poorly developed, irregular vertebrae lamprey
Presence of keratinized teeth on tongues
Fossil jawless fishes (agathans)
Present as early as Cambrian
All went extinct
Phylogenetically between cyclostomes and jawed vertebrates
Fossil agnathans: Conodontia
Widespread, found mostly in the form of tooth-like microfossils
Cambrian to Triassic
Composed of hydroxyapatite, the same mineral constituting vertebrate bones and teeth
Elements of conodont can form in a somewhat “symmetrical apparatus”
