Sponges Cnidarians Arthropods Brachiopods Bryozoans Segmented worms Molluscs Echinoderms Chordates

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

2. 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 Fossils & Evolution—Cnidaria

3. 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 Fossils & Evolution—Cnidaria

4. 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) Fossils & Evolution—Cnidaria

5. 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 Fossils & Evolution—Cnidaria

6. Basic body forms Fossils & Evolution—Cnidaria

7. 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 Fossils & Evolution—Cnidaria

8. 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 Fossils & Evolution—Cnidaria

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

10. 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) Fossils & Evolution—Cnidaria

11. Polyp andskeleton Fossils & Evolution—Cnidaria

12. 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 Fossils & Evolution—Cnidaria

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

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

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

16. 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 Fossils & Evolution—Cnidaria

17. 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” Fossils & Evolution—Cnidaria

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

19. 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. Fossils & Evolution—Cnidaria

20. Septal insertion in scleractinians Fossils & Evolution—Cnidaria

21. 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 Fossils & Evolution—Cnidaria

22. Coralevolution Fossils & Evolution—Cnidaria

23. 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 Fossils & Evolution—Cnidaria