Osteichthyes Synapomorphies
1) Lepidotrichia (segmented, dermal bone supports of fin)
2) Oral teeth on dermal bone
3) Operculum
4) Presence of lung (connected to gut tube) or swim bladder
Lepidotrichia
- Segmented, dermal bone supports of fins, different from spines
- Composite = flexible
- Basals and radials are endochondral bone
- Muscles in the fin are only at the base
- The skeleton is confined to the base of the fin, fin rays make up the majority of the fin
Oral teeth on dermal bone
- No replacement teeth (serial replacement)
- Teeth in sharks directly on 13, but Osteichthyes aren’t
Operculum
Plate of dermal bone over gill opening
Presence of lung or swim bladder
- Lung forms from an out-pocket of the gut, later becomes swim bladder
- Swim bladder has no respiratory function, only buoyancy, but some fish re-evolve respiratory function
- 2 types of swim bladder
What are the two types of swim bladder?
1) Physostomous
2) Physoclistous
Physostomous
swim bladder attached to gut and filled by swallowing air
Physoclistous
The swim bladder is independent of the gut and filled by gas exchange with the blood
Generalized feeding modes: suction, ram, biting, or combo
Most common: suction, mouth opens (protrudes forward + out) and head moves too, creates negative ambient pressure which sucks water and prey rapidly into the mouth
- Feeding modes not necessarily mutually exclusive
Sensory systems
- Scent, vision, hearing
- Pressure sensing (lateral line, and also on head)
- Touch (navigation, b/c sensory neurons in fins)
What are the three electrical systems for sensing, feeding, and communication?
1) Passive electroreception
2) Active electroreception
3) Strongly electrogenic
Bony fish don’t have electric detection organ, only sharks have that
Passive electroreception
Can only detect fields produced by other individuals
Active electroreception
Produce own weak field. When sensing, detect changes to own field (prey detection, communication = knifefish, elephantfish)
Strongly electrogenic
Stun prey. deter predators (electric eel, torpedo ray)
Ventilation through dual-pump system
1) Mouth opens, walls of mouth expand/relax, negative pressure sucks water in. Delayed pharynx opening, draws water through mouth to gills.
2) Mouth closes, squeezes water into pharynx (delayed), push by mouth pull by pharynx of water
3) Pharynx closes, opens operculum
Branchial arches 1-4 have gills; 5th partially lost
- 4 branchial arches on each side of body
- 5th is partially lost (from sharks), later becomes tooth plates in bony fish
Osmoregulation: seawater salt > fish salt > freshwater salt
Seawater: Dehydration problem: drink
- Salts: concentrated urine (holding onto as much water as possible) and exchange cells in gills
Freshwater: Overhydration problem
- Don’t drink, very dilute urine (get rid of water, takes salt out)
- Salts: exchange cells in gills, pump salts into body
External fertilization and oviparity, but otherwise tons of variety
- Vary in whether there’s a nest, clutch size, and parental care
- Varied sex assignment systems:
~ born and remain male or female
~ simultaneous hermaphrodites (both M and F at the same time)
~ sequential hermaphrodites (start as 1 sex, later change to other sex)
What are some of the ways chondrichthyans and osteichthyans are the same or different?
- Different electrical sensing capabilities, osteichthyans in general don’t have any electrical sensing capabilities
- Both have teeth, differ in origin
- Both osmoregulators
- Osteichthyans can touch via fins
- Different modes of ventilation (ventilatory pump vs none)
Sarcopterygii Synapomorphies (1 of 2 major branches of Osteichthyes)
- Cosmine in scales (mineralized tissue)
- Intercranial joint (braincase divides cranial/caudal, allows for more jaw mobility)
- Lobed fins (lost lepidotrichia structure, now have mesomeres running in middle of fin surrounded by radials then fin rays)
Sacropterygii diversity
- Actinisia (coelacanths -> live in deep, cold water, oil-filled lung)
- Other branch split into Dipnoi (lungfishes) and Tetrapoda (both have divided atrium?)
Actinopterygii Synapomorphies (other major branches of Osteichthyes)
- Ganoine in scales (different mineralized tissue)
- Single soft dorsal fin (flexible lepidotrichia)
- Keep fin rays
Most basal groups of Actinopterygii
- Polypteriformes (dorsal finlets, can walk on land)
- Other branch split into two: Acipenseriformes (reduced scaling, skin instead) and Neopterygii ( both are primarily air breathers)
Neopterygii Synapomorphies
- Mobile maxilla (related to suction feeding)
- Pharyngeal teeth concentrated on tooth plates derived from dorsal-most element of branchial arches 2-4
- Reduced basals in paired fins
- Fewer hypurals (specialized vertebrae) in caudal fin (tails become more symmetrical externally)
