vertebrate origins Flashcards
chordate features
dorsal, hollow nerve chord, notochord, pharyngeal slits; post anal tail
vertebrate features
neural crest cells, dermal bone, often paired appendages, closed circulation and red blood cells, cephalisation, skull
major chordate subphyla
- Urochordata
- Craniata
- Cephalochordata
Craniates
- chordates with cephalisation and bone/cartilage
- essentially vertebrates, but may lack vertebrae
features of fish
(not taxonomic ranking)
- pokibothermic , aquatic chordate
- tends to swim, gills main respiratory organ, may have appendages. covered in scales
- be ectothermic (many exceptions)
Origin of bone
- cartilage (tough, semitransparent, elastic, flexible, glycoprotein strengthened bay collagen)
- mineralised skeleton can be (external (dermal bone) internal, derived from cartilage precursors (endochondral))
- solid support attachment of muscles
- fast efficient, locomotion - avoid predators and catch prey
- storehouse of chemicals for metabolism
- protection
Ostracoderms
- dominant fishes in Silurian
- bony shield over head and thorax
- often small, but some large(>1m)
- vertebrate innovations (cellular bone, dentine-like tissue, paired limbs, intricate sensory line systems, complex eye muscles, inner ear with 2 semicircular canals
- bony but still no jaws
- 4 superclasses
Pteraspidomorphi (superclass ostracoderms)
generally small (10-20cm) but some uptown 1.5m
benthic filter feeders
evolved reduced armour, narrower head shield, lateral projections
Anaspida (superclass ostracoderms)
- small (<15cm) fusiform, copressed
- benthic parasite / detrital feeders
- marine and FW
- fin-like projections and muscles and internal skeleton -> manoeuvrability
- overlapping tuberculate scales
Thelodonti (superclass ostracoderms)
- small (10-20cm), fusiform, depressed, large head, horizontal mouth
- hypocercal tail, dorsal & anal fins: benthic
- forktail form - supra-benthic
- covered with characteristic scales or dentricles
- stomach
- lateral line
Osteostracomorphi (superclass ostracoderms)
- abundant and diverse
- large, anterior, bony shield with eye, nose and pineal opening
- ossification of endoskeleton
- epicercal tail, body form and paired fins : creates lift
- complex brain
Myxinomorphi (Craniata)
- 70 species living in one class : Myxini
- temperate/cold temp ocean
- below 30m in depth
- seawater : isosmotic
- sister group to vertebrates : lack even primitive vertebrae
- no true eyes
- mud-burrowing species extremely hypoxia tolerant
- predators of benthic inverts and scavengers (burrow into prey)
- 70 - 200 pairs of slime glands exude mucous and thread cells
Petromyzontomorphi (Craniata)
- 38 living species in one class : Petromyzontida
- functional eyes, cerebellum, separate ventral and dorsal roots of the spinal nerves
- olfactory and respiratory pathways are separated
- fw species : may be parasitic
- anadromous species : all are parasitic
Hagfishes and Lampreys : similarities
- eel-like, scale-less, jawless forms
- produce pathogen-specific defensive substances : ‘variable lymphocyte receptors’
- tongue possesses keratinous, replaceable teeth
- no stomach
Mucus production (Hagfishes and Lampreys)
Hagfishes : Yes
Lampreys : No
