1. Lecture 7: Phylum Cnidaria, Part 2
Invertebrate Zoology
Lecture 7: Phylum Cnidaria, Part 2

2. Class Hydrozoa Siphonophore Photo:
K. Raskoff / Monterey Peninsula College

3. Class Hydrozoa Order Hydroidea: the hydroids
Polyp form often colonial, branched (Obelia)
Includes feeding and reproductive polyps
Coenosarc: common gastrovascular cavity

4. Class Hydrozoa
Order Hydroidea: life cycle (Obelia sp.)

5. Planula larvae
Some solid, others with g.v. cavity
Move via cilia

6. Class Hydrozoa Order Siphonophora Two medusa types
Swimming
Sexual Reproduction
Polyps: feeding, defense, asexual reproduction
Predators!
Gas-filled float
Many variations!

7. Class Hydrozoa Order Siphonophora Cormidium “colony within a colony”
Detachable

8. Class Hydrozoa
Order Chondrophora (Velella velella, by-the- wind sailors):
Free-floating polyp
Secondary polyps (feeding, reproduction)
Tiny, free-living medusae

9. Class Hydrozoa Order Trachylina: life cycle No true polyp stage
Planula develops into medusa

10. Class Hydrozoa Order Hydrocorallina: hydrocoral, fire coral
Not a “true” coral! (True coral = C. Anthozoa)
Calcareous skeleton
Some with symbiotic zooxanthellae
Polyps within chambers
Reduced medusa stage
Why called “fire” coral?

11. Class Scyphozoa Semaeostomae (most jellies) Stauromedusae
Key predators (impact?)
Stauromedusae
Sessile medusa or polyp?
Develop from planula larva

12. Class Scyphozoa Life cycle, Semaeostomae (Aurelia)
Key: strobilation of polyp  ephyra  medusa

13. Class Scyphozoa
Pelagia
Note trailing mouth lobes

14. Class Scyphozoa Life cycle, Pelagia
No polyp stage: planula  ephyra medusa

15. Class Cubozoa: box jellies
Polyp  medusae via direct metamorphosis
Chironex: deadliest toxin known

16. Class Anthozoa
Anemones
Coral
Sea pansies
Gorgonians
Etc…

17. Class Anthozoa Generalized life history: no medusae
Asexual reproduction also important

18. Class Anthozoa: Subclass Hexacorallia
Order Actiniaria: solitary anemones

19. Class Anthozoa: Subclass Hexacorallia
Order Corallomorpha
Anemone-like, but with clubbed tentacles
Clonal form shown; clone wars occur!

20. Class Anthozoa: Subclass Hexacorallia
Order Scleractina: stony (“true”) corals
Deposit CaCO3 skeletons
Contain mutualistic zooxanthellae
Some are reef builders
Clubbed tentacles; polyps open at night…

21. Class Anthozoa: Subclass Hexacorallia
Order Scleractina: stony (“true”) corals
Gastrovascular cavity connects polyps
Mutualistic zooxanthellae within gastrodermis
= acontia
Mesentery =

22. Class Anthozoa: Subclass Hexacorallia
Order Scleractinia: stony (“true”) corals
Initial colony: from planula larva produced sexually (VIDEO!)
Colony growth: asexual division
Fragmentation  “new” colony

23. Class Anthozoa: Subclass Ceriantipatharia
Order Ceriantharia: tube anemones
Double whorl of tentacles
Build sand tubes; capable of burrowing

24. Class Anthozoa: Subclass Octocorallia
Features of subclass
Eight-tentacled, pinnate polyps
Eight complete mesenteries

25. Class Anthozoa: Subclass Octocorallia
Order Gorgonacea: sea whips, sea fans
skeleton of gornonin (protein), and/or calcareous spicules
often highly branched in one plane
Oriented perpendicular to prevailing current

26. Class Anthozoa: Subclass Octocorallia
Order Alcyonacea: soft corals
fleshy, sometimes tree-like
pump water throughout the colony
Scubatravel.com

27. Class Anthozoa: Subclass Octocorallia
Order Pennatulacea: sea pens, sea pansies
Main body = polyp; has secondary, lateral polyps
Gastrozooids (feeding)
Siphonozooids (water flow)
Calcareous spicules provide structure
© Alvaro E. Migotto

28. Class Anthozoa: Subclass Octocorallia
Order Stolonifera: organ pipe coral
Calcareous "spicules" provide structure
Polyps within tubes or on stalks