1. Share characteristics with echinoderms and chordates
Phylum Hemichordata
Marine worms
Share characteristics with echinoderms and chordates
Deuterostomes (radial cleavage)
Pharyngeal gill slits
Some have dorsal, hollow nerve cord

2. Live in burrows in fine sediments
Class Enteropneusta
Acorn worms ~ 70 species
Live in burrows in fine sediments

3. Proboscis for burrowing and feeding
Acorn worms
Proboscis for burrowing and feeding

4. Mostly deposit feeders
Acorn worms
Mostly deposit feeders

5. Mouth – esophagus – pharynx – intestine - anus
Digestion
Mouth – esophagus – pharynx – intestine - anus

6. Gill slits connected to pharynx
Respiration
Gill slits connected to pharynx
Cilia move water through mouth, out pharynx

7. Closed system with blood and vessels
Circulation
Closed system with blood and vessels

8. Similar to echinoderms – no brain Nerve cords connect all regions
Nervous system
Similar to echinoderms – no brain
Nerve cords connect all regions

9. Dioecious = separate sexes Gonads produce gametes
Reproduction
Dioecious = separate sexes
Gonads produce gametes
External fertilization

10. Similar appearance to echinoderm larva Ciliated bands
Tornaria larva
Similar appearance to echinoderm larva
Ciliated bands

11. Colonial zooid Construct rigid tubes Ciliated tentacles U-shaped gut
Class Pterobranchia
Colonial zooid
Construct rigid tubes
Ciliated tentacles
U-shaped gut
Pharyngeal gill slits

12. New topic: invertebrate evolution
Original prediction for larva type:
Ancestral condition = external fertilization, non-feeding larvae
More recently evolved = internal fertilization, feeding larvae
Both conditions are scattered across phyla

13. Evolution across the Central American Isthmus
Formed 2-3 mya
Enough time for evolution?

14. Different environments?
Western Atlantic
water depth varies among islands, different climate – no upwellings, less El Nino effects, higher evaporation rate, lower productivity

15. Different environments?
Eastern Pacific
Deeper, upwellings bring nutrients, El Nino effects strong, stronger tidal effects

16. Different environments?
Western Atlantic: sea grass beds common
Not in EP

17. Different environments?
Western Atlantic: coral reefs large – hundreds of acres, higher S
Small outcrops in EP, lower S

18. Large swimmers can still disperse around continents
Different taxa?
Large swimmers can still disperse around continents
Not smaller-bodied taxa

19. Similar mitochondrial DNA differences for all crustracea
Genetic differences?
Similar mitochondrial DNA differences for all crustracea
Other groups – variation high

20. Life history differences?
Echinoderm, bivalve eggs smaller in open ocean EP = higher productivity

21. Many examples of incompatibility, but not distinct species yet
Speciation?
Many examples of incompatibility, but not distinct species yet