This document summarizes the phyla Cnidaria and Ctenophora. Cnidaria includes jellyfish, corals, sea anemones and hydras. They have stinging cells called cnidocytes and can have a polyp or medusa body form. Ctenophora includes comb jellies and have rows of cilia used for locomotion. They lack specialized organ systems and reproduce via a free-swimming larval stage. Both phyla are marine and diploblastic, with tissues but no true organs. Cnidaria have nematocyst stinging cells and Ctenophora have comb rows of cilia.

1. Cnidaria and Ctenophora
Chapter 13

3. Phylum Cnidaria (cnidarians)
Diversity - 9,000 species (Hickman et al. 2017)
- 10,105 species (Zhang et al. 2011)
5 classes - Anthozoa, Staurozoa, Scyphozoa, Cubozoa, Hydrozoa

4. Phylum Cnidaria (cnidarians)

5. Phylum Cnidaria (cnidarians)

6. Phylum Cnidaria (cnidarians)

7. Phylum Cnidaria (cnidarians)

8. Phylum Cnidaria (cnidarians)
Where found?
Widespread in marine waters (esp. shallow, warm tropical); few in
freshwater.
General characteristics
- Diploblastic with radial or biradial symmetry
- Tissues, but no organs.
Mostly sessile; motile species are slow moving
Predators of much more motile animals
Cnidocytes with with nematocyst

9. Phylum Cnidaria (cnidarians)
General characteristics (cont.)
May live symbiotically (obligate
and facultative) with other animals.
Anthozoa
Staurozoa
Scyphozoa
Cubozoa
Hydrozoa

10. Phylum Cnidaria (cnidarians)
Body plan
Dimorphism - polyp or medusa
- Polyp - tubular body; mouth surrounded by tentacles, leads to
gastrovascular cavity; attached to substrate by pedal disc
- Reproduce by budding - if buds detach = clones; if buds remain attached = colony
- Colonies may exhibit polymorphism (single genotype expressing multiple
phenotypes, zooids)

11. Phylum Cnidaria (cnidarians)
Body plan
Dimorphism - polyp or medusa
- Polyp

12. Phylum Cnidaria (cnidarians)
Body plan
Dimorphism - polyp or medusa
- Medusa - bell-shaped (or umbrella-shaped) body; mouth on concave side
and surrounded by tentacles; usually free-swimming; sensory structures
at margins of bell.
- Generally reproduce sexually.

13. Phylum Cnidaria (cnidarians)
Body plan
Dimorphism - polyp or medusa
- Medusa

14. Phylum Cnidaria (cnidarians)
Body plan
Dimorphism - polyp or medusa

15. Phylum Cnidaria (cnidarians)
Body plan
- Body wall - outer epidermis, inner gastrodermis, mesoglea between.
- Epidermis - epitheliomuscular, sensory, nerve, and cnidocyte cells.
- Mesoglea - gelatinous (95-96% water), bridge between epidermis and gastrodermis; acts as
elastic skeleton.
- Gastrodermis - cells for digestion and absorption (nutritive muscle cells), gland cells, interstitial
cells.

16. Phylum Cnidaria (cnidarians)
Body plan
- Body wall

17. Phylum Cnidaria (cnidarians)
Body plan
- Cnidocytes
- Produce over 20 organelles (cnidae); nematocysts are one type
- Nematocysts are thread-like, may bear barbs, spines, and deliver toxins (some may not).
- Operculum with cnidocil trigger (some mechanical, some chemical)
- Very fast firing

18. Phylum Cnidaria (cnidarians)
Body plan
- Cnidocytes

19. Phylum Cnidaria (cnidarians)
Body plan
- Cnidocytes

20. Phylum Cnidaria (cnidarians)
Body plan
- Cnidocytes

21. Phylum Cnidaria (cnidarians)
Body plan
- Cnidocytes

22. Phylum Cnidaria (cnidarians)
Homeostatic functions and structures
- No excretory system (accomplished by diffusion)
- No respiratory system (accomplished by diffusion)
- No circulatory system (accomplished by diffusion)
- No osmoregulatory system (accomplished by diffusion)
- No temperature regulation

23. Phylum Cnidaria (cnidarians)
Nervous system
- Nerve net (diffuse nervous system)
- Lack concentrations of nerve cells (no
brain or ganglia)
- Bidirectional travel of nerve impulses;
lack insulating material (myelin)

24. Phylum Cnidaria (cnidarians)
Class Hydrozoa
- Mostly marine and colonial; typical life-cycle with both asexual polyps and
sexual medusae.
Hydroid colonies
- Broadly, contain base, stalk, with one or more terminal zooids

25. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Hydroid colonies (e.g., Obelia)
- Broadly, contain base, stalk, with one or more terminal zooids
- Base = hydrorhiza; stalk = hydrocauli
- Hydrocauli composed of living (coenosarc) and non-living (perisarc) elements.
- Feeding zooids are hydranths; reproductive zooids are gonangium.

26. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Hydroid colonies (e.g., Obelia)

27. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Hydroid medusa (e.g., Gonionemus)
- Possess a velum
- Mouth suspended on a manubrium
- Endowed with statocysts and ocelli

28. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Hydroid medusa (e.g., Gonionemus)

29. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Solitary hydroid (e.g., Hydra)
- Basal disc for attachment
- Mouth on hypostome
- Dioecious and capable of both sexual and asexual reproduction

30. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Solitary hydroid (e.g., Hydra)

31. Phylum Cnidaria (cnidarians)
Class Hydrozoa
Colonial hydroid (e.g., Physalia)
- Portuguese man-of-war
- Pneumatophore
- Tentacles are zooids

32. Phylum Cnidaria (cnidarians)
Class Scyphozoa
- Most of the large jellies; drift or swim in seas and oceans.
- Lack velum
- Margin of bell is scalloped
- At indentations, rhopalium are present (statocyst and ocelli are associated)
- Manubrium forms four oral arms
- Dioecious

33. Phylum Cnidaria (cnidarians)
Class Scyphozoa
Typical scyphozoan (e.g., Aurelia)
- Reproduction - zygote to planula to
scyphistoma to strobila to ephyrae
to mature jelly.

34. Phylum Cnidaria (cnidarians)
Class Scyphozoa
Typical scyphozoan (e.g., Aurelia)
- Reproduction - zygote to planula to
scyphistoma to strobila to ephyrae
to mature jelly.

35. Phylum Cnidaria (cnidarians)
Class Scyphozoa
Atypical scyphozoan (e.g., Cassiopeia)
- The “upside-down jelly”
- Symbiotic zooxanthellae in tissues
- Generate food for themselves and jelly
via photosynthesis

36. Phylum Cnidaria (cnidarians)
Class Scyphozoa
Atypical scyphozoan (e.g., Cassiopeia)
- The “upside-down jelly”
- Symbiotic zooxanthellae in tissues
- Generate food for themselves and jelly
via photosynthesis

37. Phylum Cnidaria (cnidarians)
Class Staurozoa
- Once considered part of Scyphozoa
- Solitary, stalked polyp
- Sexual reproduction; planula is non-
swimming
- Lack a medusa stage

38. Phylum Cnidaria (cnidarians)
Class Cubozoa
- Once considered part of Scyphozoa
- Medusa predominates; polyp reduced or unknown
- Bell has squared appearance, with tentacles at “corners”.
- Rhopalia presents between “corners” - eyes and other sense organs present
- Umbrella margin not scalloped; velarium present (homoplasy of vellum)
- Some with powerful stings.

39. Phylum Cnidaria (cnidarians)
Class Cubozoa

40. Phylum Cnidaria (cnidarians)
Class Anthozoa - flower animals
- Polyp only; no medusa
- All marine; deep to shallow; cold to warm; solitary to colonial.
- Gastrovascular cavity is large in comparison to other cnidarians.
- Three subclasses - Hexacorallia - sea anemones, hard corals
Ceriantipatharia - tube anemones and thorny corals
Octocorallia - sort and horny corals, sea pens, sea fans

41. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Hexacorallia
Sea anemones
- Large, heavy polyps
- Attach to substrate with pedal disc; mouth on oral disc
- Mouth slit-shaped, with siphonoglyph to create water currents
- Mouth to pharynx to gastrovascular cavity
- GV cavity divided by complete (primary) and incomplete (secondary) septa
- Incomplete septa with septal filaments, may extend out of body as acontia
threads.

42. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Hexacorallia
Sea anemones

43. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Hexacorallia
Sea anemones

44. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Hexacorallia
Hexacorallian corals - true or stony
corals
- Miniature anemones in calcareous
cups

45. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass
Ceriantipatharia
Tube anemones, thorny corals
- Low diversity; tropical
- Tube anemones solitary
- Thorny corals colonial

46. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Octocorallia
Soft corals, sea pens, sea fans
- Parts in 8s
- All colonial; gastrovascular cavities communicate with each other
- Very colorful

47. Phylum Cnidaria (cnidarians)
Class Anthozoa, subclass Octocorallia
Soft corals, sea pens, sea fans

48. Phylum Ctenophora (ctenophores)
Diversity - 150 species (Hickman et al. 2017)
- 242 species (Zhang 2011)
Where found?
- All are marine; all waters, but more abundant in warm waters

49. Phylum Ctenophora (ctenophores)

50. Phylum Ctnenophora (ctenophores)
General characteristics
- Traditionally diploblastic; but some debate
- Eight, equally-spaced rows of comblike plates of cilia
- Rows = comb rows; plates = combplates
- Used in locomotion
- No head, but oral-aboral axis present
- Mouth to pharynx to digestive tract to anal pore
- Body is transparent with gelatinous layer from ectoderm and endoderm both
- Tentacles may be present and may have colloblasts (glue cells) for prey
capture

51. Phylum Ctenophora (ctenophores)
Homeostatic functions and structures
- Respiration and excretion by diffusion
- No circulatory, osmoregulatory, or temperature regulation
Nervous system
- Nerve net
- Statolith present at aboral end (controls orientation)
- Epidermis bears abundant chemo and tactile sensory cells.

52. Phylum Ctenophora (ctenophores)
Reproduction
- Most are monecious
- Cydippid larva is free-swimming, and transitions into an adult without
metamorphosis
Bioluminescence
- Most ctenophores are bioluminescent (e.g., produce chemical light)

53. Phylum Ctenophora (ctenophores)