1. Fossils & Evolution—Cnidaria1 Sponges Cnidarians Arthropods Brachiopods Bryozoans Segmented worms Molluscs Echinoderms Chordates Multicellular animals Animals with nerve and muscle cells Coelomates (true body cavity) Deuterostomes (anus forms before mouth)

2. Fossils & Evolution—Cnidaria2 Cnidarians—Stuff to know All bold font morphologic terms in text Classification and stratigraphic ranges of paleontologically important groups Skeletal mineralogy Septal insertion patterns in rugosans and scleractinians Hermatypic vs. ahermatypic ecology

3. Fossils & Evolution—Cnidaria3 Cnidarians—Be able to identify: Order Scleractinia –Genus Diploria; Genus Montastrea; Genus Dichocoenia Order Rugosa –Genus Hexagonaria; Genus Pachyphyllum Order Tabulata –Genus Favosites; Genus Halysites; Genus Aulopora

4. Fossils & Evolution—Cnidaria4 Cnidaria—Phylum overview Colonial and solitary invertebrates Examples include hydroids, jellyfish, sea anemones, corals Two body layers (ectoderm and endoderm) separated by middle, non-cellular (“jelly”) layer (mesogleoa) No coelom (no true body cavity) No organs Primary radial symmetry Possess specialized stinging structures (nematocysts)

5. Fossils & Evolution—Cnidaria5 Cnidaria—Phylum overview (cont.) Body is a polyp (mouth up) or medusa (mouth down) Digestive system is a central mouth that leads to a digestive cavity (enteron) Mouth may be surrounded by tentacles Muscle cells and nerve cells facilitate simple movements

6. Fossils & Evolution—Cnidaria6 Basic body forms

7. Fossils & Evolution—Cnidaria7 Cnidaria—Phylum overview (cont.) Skeleton may be absent, internal, or external –If present, organic or calcareous Aquatic (fresh and marine) Suspension feeders Sessile, planktonic, or nektonic Stratigraphic range is Late Proterozoic (Ediacaran) to Recent

8. Fossils & Evolution—Cnidaria8 Classification Class Hydrozoa (“hydroids,” unimportant as fossils) Class Scyphozoa (jellyfish, unimportant as fossils) Class Anthozoa (true corals and others) –Exclusively marine –Polyp stage only; no medusa –Free-swimming larvae

9. Fossils & Evolution—Cnidaria9 Cnidaria classification Note: Permian scleractinian-like forms are now known

10. Fossils & Evolution—Cnidaria10 Skeletal morphology Coral skeletons are external and calcareous –Aragonite or calcite Skeleton is secreted by the epidermis at the base of the polyp Skeleton consists of basal plate, radial septa, and outer wall (theca) As skeleton grows upward, new basal plates may be added –Tabulae (transverse plates) –Dissepiments (smaller, curved plates)

11. Fossils & Evolution—Cnidaria11 Polyp and skeleton

12. Fossils & Evolution—Cnidaria12 Skeletal morphology (cont.) Polyp occupies the calice, the part of the skeleton above the last-formed tabula or dissepiments Skeleton of one coral (solitary or colonial) is a corallum Skeleton of one polyp in a colony is a corallite Skeletal tissue between corallites in a colony is coenosteum

13. Fossils & Evolution—Cnidaria13 Skeletal morphology (cont.)

14. Fossils & Evolution—Cnidaria14 Skeletal morphology (cont.)

15. Fossils & Evolution—Cnidaria15 Skeletal morphology (cont.)

16. Fossils & Evolution—Cnidaria16 Septal insertion Tabulates lack septa or possess only minor septa Order of septal insertion is the most important aspect of classification in the rugose corals and scleractinians

17. Fossils & Evolution—Cnidaria17 Septal insertion in Rugose corals First six septa are “protosepta” –Stage 1: cardinal and counter septa –Stage 2: alar septa (on either side of cardinal septum) –Stage 3: counterlateral septa (on either side of counter septum) All subsequent septa (metasepta) are added on either side of cardinal septum and on counter side of alar septa Septa cluster into four quadrants  hence, “Tetracorals”

18. Fossils & Evolution—Cnidaria18 Septal insertion in Rugose corals x = cardinal sector y = alar sector Fossulae = gaps between sectors Six protosepta

19. Fossils & Evolution—Cnidaria19 Septal insertion in scleractinians Stage 1: six protosepta Stages 2 and higher: metasepta added in the center of spaces between existing septa –Metasepta added in groups of 6, 12, 24, 48, etc.

20. Fossils & Evolution—Cnidaria20 Septal insertion in scleractinians

21. Fossils & Evolution—Cnidaria21 Coral evolution Among the common corals, tabulates (Early Ordovician-Permian) were first to originate Rugose corals (Middle Ordovician-Permian) might have evolved from tabulates or they might have a separate ancestor Scleractinians might have evolved from rugosans (?), or from a naked sea anemone –Permian “scleractinian-like” forms are known –Late Paleozoic aragonitic rugosans are known –No Early Triassic corals are known –Pattern of septal insertion is quite different in rugosans and scleractinians

22. Fossils & Evolution—Cnidaria22 Coral evolution

23. Fossils & Evolution—Cnidaria23 Coral ecology and reefs Hermatypic = reef corals that possess zooxanthellae (symbiotic algae) –Shallow, tropical water (25–29°C; < 90 m depth) –Rapid skeletal growth –Oligotrophic (low nutrient) environments Ahermatypic = non-reef corals without zooxanthellae –Wide environmental range (all latitudes) –Up to 6000 m depth; down to 1°C temp