4.3 Chordates

Deuterostomia

• blastopore becomes anus

• radial cleavage

• indeterminate cleavage

• primitiive dorsal nervous system

• primitive central circulatory system

Chordates characteristics

1. Notochord: flexible rod shaped structure that runs along nerve chord

2. Dorsal hollow nerve chord: parallel to notochord

3. pharyngeal slits: gills, parts of ear and tonsils

4. Post-anal tail

Phylum Chordata Subgroups

• cephalochordata (invertebrates)

• Urochordata (invertebrates)

• Vertebrata

Urochordata

• all 4 chordate features

• adults have pharyngeal slits

• tunicates: sea squirts

Cephlachordata

• “head cord”

• all 4 chordate features

• Lancelets: filter feeders in mud

Vertebrata

• largest group of chordates

• cranium

• all 4 chordate features

• vertebrae

Fish

• jawless fish

• jawed fish

Chordate Jawless Fishes

• Hagfish: poorly developed cranium and notochord

• transitional group

• have gills

• scavengers and parasites

Vertebrate Jawless fishes

• lampreys: possess a skull

• parasitic

Gnathostomata- jaw mouth

• jaw derived from gill arches

• 2 sets of fins

Chondrichthyes

• cartilagionous fishes

• oldest group

• sharks rays

• jaws/skeleton made of cartilage

• evolution of teeth (modified scales)

• gill slits lack hard covering

Osteichthyes- boney fishes

• ossified skeleton

• largest class of vertebrates

• gills covered by operculum

• swim bladder

• 1. gills

• 2. lungs -in bony fishes

• 3. swim bladder

Actinopterygii- ray finned fishes

• slender bones in fin

• gills are most common

• bichirs- gills and lungs

Sarcopterygii- lobed finned fishes

• lobed fins supported by arrangment of bones similar to tetrapods

• lungfish and coelacanths- gills and lungs

Practice: 2-3 defining characteristics for each group