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

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Presentation on theme: "Phylum Hemichordata Marine worms Share characteristics with echinoderms and chordates Deuterostomes (radial cleavage) Pharyngeal gill slits Some have dorsal,"— Presentation transcript:

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

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

3 Acorn worms Proboscis for burrowing and feeding

4 Acorn worms Mostly deposit feeders

5 Digestion Mouth – esophagus – pharynx – intestine - anus

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

7 Circulation Closed system with blood and vessels

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

9 Reproduction Dioecious = separate sexes Gonads produce gametes External fertilization

10 Tornaria larva Similar appearance to echinoderm larva Ciliated bands

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

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


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