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
Live in burrows in fine sediments Class Enteropneusta Acorn worms ~ 70 species Live in burrows in fine sediments
Proboscis for burrowing and feeding Acorn worms Proboscis for burrowing and feeding
Mostly deposit feeders Acorn worms Mostly deposit feeders
Mouth – esophagus – pharynx – intestine - anus Digestion Mouth – esophagus – pharynx – intestine - anus
Gill slits connected to pharynx Respiration Gill slits connected to pharynx Cilia move water through mouth, out pharynx
Closed system with blood and vessels Circulation Closed system with blood and vessels
Similar to echinoderms – no brain Nerve cords connect all regions Nervous system Similar to echinoderms – no brain Nerve cords connect all regions
Dioecious = separate sexes Gonads produce gametes Reproduction Dioecious = separate sexes Gonads produce gametes External fertilization
Similar appearance to echinoderm larva Ciliated bands Tornaria larva Similar appearance to echinoderm larva Ciliated bands
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
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
Evolution across the Central American Isthmus Formed 2-3 mya Enough time for evolution?
Different environments? Western Atlantic water depth varies among islands, different climate – no upwellings, less El Nino effects, higher evaporation rate, lower productivity
Different environments? Eastern Pacific Deeper, upwellings bring nutrients, El Nino effects strong, stronger tidal effects
Different environments? Western Atlantic: sea grass beds common Not in EP
Different environments? Western Atlantic: coral reefs large – hundreds of acres, higher S Small outcrops in EP, lower S
Large swimmers can still disperse around continents Different taxa? Large swimmers can still disperse around continents Not smaller-bodied taxa
Similar mitochondrial DNA differences for all crustracea Genetic differences? Similar mitochondrial DNA differences for all crustracea Other groups – variation high
Life history differences? Echinoderm, bivalve eggs smaller in open ocean EP = higher productivity
Many examples of incompatibility, but not distinct species yet Speciation? Many examples of incompatibility, but not distinct species yet