1. CHAPTER 13 – The Cnidarians (Radiate Animals)
Fig. 13.CO

2. Phylum Cnidaria
Hydra, jellyfish, coral, & sea anemones

3. Jellyfish can be funny….

5. General Characteristics
Radial symmetry
Their body is arranged around an oral-aboral axis
Oral end terminates in a mouth that is surrounded by tentacles
Good for sessile; sedentary lifestyle
Reach the tissue level of organization
Cells are organized into groups of tissues that work together
Contains 2 tissue layers (diploblastic) including: epidermis (gives rise to the outer body wall) and gastrodermis(gut)

6. General Characteristics
Acoelomated organism- they contain NO body cavity
All are carnivores
Over 9,000 species are in the phylum
No system for circulation, respiration or excretion-> occur by diffusion
Some cnidarians can regenerate lost parts or even a complete body
Most cnidarians are dioecious (2 forms: male and female)
All named for the presence of cells called Cnidocytes: cells that contain the stinging organelle called nematocysts
Found only in cnidarians

8. General Characteristics
Diploblastic: contain 2 well-defined germ layers: ectoderm (epidermis) and endoderm(gastrodermis)
Examples include: Hydras, jellyfish, sea anemone, corals, Portuguese man of war, box jelly fish
Movement: mostly sessile, some move or “swim” slowly
All contain some type of Gastrovascular cavity with one opening for food intake and elimination of waste

10. General Characteristics
Both the outer (epidermis) and inner ( gastrodermis) contains nerve cells that are arranged in a loose network called a Nerve Net
Innervates their primitive muscles that extend form the epidermal and gastrodermal cells
Stimulus in one part will spread across the whole body by the network

11. General Characteristics
Location
Found mostly in marine habitats (some freshwater)
Most abundant in warm (tropical), shallow, marine waters
Colonial organisms can be found attached to rocks, animals, or wharves

12. Ecological Role Predator/Prey Relationships
Neurotoxins in medical research
Coral- jewelry, reef building
Symbiosis with other organisms
Coral reefs- habitat for many
Great biodiversity
Protect the coastline

13. Symbiotic Relationships
Mutualism
Hydroids and sea anemones can live on hermit crab shells
Algal cells live in the tissue of cnidarians
Clown fish and sea anemone
Portuguese Man of War and the Nomeus fish

17. Cnidarian Body Plans Dimorphism
Existence of 2 morphological types within the same species
Allows the organism to obtain food from different locations
All cnidarians fit into one of the following types:
*polyp
*medusa

18. Cnidarian Body Plans Polyp (hydroid): Fits a sessile lifestyle
Can be found singly or in colonies
Structure: tubular body with a mouth at one end (directed upward) surrounded by tentacles
The aboral end is attached to a substrate

19. Polyp Structure

20. Cnidarian Body Plans Medusa Jellyfish form
Fits the swimming/floating lifestyle
Mobile, move by weak contractions of body
Bell or umbrella shape
Mouth is usually directed downward and centered on the concave side and tentacles extend from the rim
“mouth down” version of the polyp
Contains more mesoglea (middle jelly-like layer) than polyp stage

21. Polyp vs. Medusa

23. Cnidocyte/Nematocyst
Cnidarians are named after the presence of cnidocytes: the stinging cell of cnidarians that produces the nematocyst
Equivalent to the container(gun) that contains the stinging organelle (bullet)
Nematocyst: the stinging organelle contained within the cnidocyte
Most characteristic structure
Helps with taxonomic classification
Over 20 different types of nematocysts

24. Structure of the Nematocyst
Enclosed within the cnidocyte (made of chitin)
All cnidocytes (except for Anthozoa class) have a cnidocil- modified cilium that triggers the nematocyst to eject
Tactile or chemical stimulation causes the nematocyst to discharge(prey swimming)
After discharge the cnidocyte is absorbed and a new one replaces it

25. Structure of the Nematocyst
Operculum: the covering (lid) that encloses the nematocyst inside the cnidocyte
Triggered to open through a change in pressure
Effects (types) of the nematocysts
Barbs: (not found in all)
Penetrants: inject poisons
Volvents: Long tentacle (string like); entangles prey
Glutinants: secretes an adhesive

27. Steps of release for a nematocyst
Stimulation of the cnidocil
The operculum opens
When the operculum opens there is a change in pressure that forces the nematocyst out
The nematocyst is ejected inside out
Poisons may be injected when it penetrates the prey

28. Cnidocyte: Before and After Discharge

30. Nerve Net The simple nervous system of cnidarians
Variation of the nerve net is found between the classes
Cnidarians have neurotransmitters on both sides of their synapses (junction between 2 nerve cells) this functions to transmits impulses in both directions
Located in the gastrodermis and epidermis
Forms 2 interconnected nerve nets

31. Nerve Net
They do form a simple neuromuscular system- their sensory nerve net plus they contain contractile fibers in their body wall to coordinate muscular contractions
They do not have:
Myelin covering their axons
Central nervous system

32. Nerve Net

33. 4 Classes of Cnidarians Class Hydrozoa (Hydra, PMOW, Obelia)
Class Scyphozoa (common jellyfish)
Class Cubozoa (box jelly)
Class Anthozoa (sea anemone and coral)

34. Class Hydrozoa General Characteristics:
Mostly marine (except freshwater hydra)
Most are colonial
Most have a sexual (medusa) and asexual (polyp) lifecycle
Examples we will discuss include:
Freshwater hydra- only has a polyp stage
Obelia
PMOW

35. Freshwater Hydra Belong to class Hydrozoa
Are solitary animals (not colonial)
Found in freshwater environments attached to anything…rocks, aquatic leaves…
Only found in the polyp stage (no medusa stage)
Feed mainly on plankton

37. Body Plan of the Hydra
Cylindrical tube with a point of attachment at the bottom and mouth at the top of the tube surrounded by tentacles
Contains the following parts
Basal disc
Located at the bottom of the tube body
Serves as the site for attachment
Secretes substances for adhesion
Can produce gas bubble at the end of the basal disc for floating

39. Body Plan of the Hydra Hypostome Mouth Gastrovascular cavity
Cone shaped elevation
Mouth is at the center
Surrounded by tentacles
Mouth
Ingests food
Gastrovascular cavity
Open cavity that is surrounded by the body wall
Site of extracellular digestion

40. Body plan of the Hydra

41. Body wall of the Hydra Surrounds the GVC Consists of 3 layers
Epidermis (outer layer)
Gastrodermis (inner layer)
Mesoglea (middle layer)

42. Epidermis of the Hydra Outer layer that serves as protection
Composed of several cell types
Epitheliomuscular cells
Interstitial cells
Gland cells
Nerve cells
Sensory cells
Cnidocytes

43. Epitheliomuscular Cells
Composes the majority of the epidermis
Functions to protect the hydra and to produce muscular contractions

44. Interstitial Cells Located at the base of the epitheliomuscular cells
Functions as stem cells to turn into almost any other cell type (cnidoblasts, sex cells, buds, nerve cells)
***What type of sponge cell does this sound like?

45. Gland Cells Located on the basal disc and around the mouth
Functions to secrete adhesive or lubrication

46. Cnidocytes Contain nematocysts
Function to protect the organism and to trap and kill food

47. Sensory Cells Located around the mouth, tentacles, or basal disc
Allows the organism to be stimulated by the environment and to be aware of its surroundings
Structure: one end had flagella for stimulation and the other end goes to the nerve cells

48. Nerve Cells
Connects with sensory cells, other nerve cells, cnidocytes, or muscular cells
Coordinates all of the activities

49. Body wall of the Hydra

50. Gastrodermis of the Hydra
Lines and directly touches the GVC
The following cell types are found in the gastrodermis:
Nutritive-muscular cells
Interstitial cells (performs the same function as in the epidermis- they act as stem cells)
Gland cells

51. Nutritive-muscular cells
Contain cilia to create a flow of food, water and nutrients inside the GVC
Tall cells that contain food vacuoles
Absorbs, digests and circulates food and fluids
Site of intracellular digestion

52. Gland cells
Gland cells in the gastrodermis are located around the hypostome and inside the column
Function:
Hypostome gland cells secrete lubricant and digestive enzymes into the GVC
Inside the GVC the gland cells secrete digestive enzymes

53. Gastro-vascular cavity
Open space inside the cnidarian
Filled with water to act as a hydrostatic skeleton (provides support)
Lined with gland cells to help with digestion
Extracellular digestion occurs in the GVC

55. Mesoglea Location: in between the epidermis and gastrodermis
Structure: non cellular, gelatinous material composed mainly of water
Function: support and flexibility
Mesoglea is thickest in the stalk (strength)
Mesoglea is thinnest in the tentacles (flexibility)

56. Locomotion of Hydra The Hydra can move in 3 ways:
Glide on basal disc (bottom of the organism)
Bend over and attach tentacles to the surface
Gas bubble

57. Feeding and Digestion: Hydra
Hydras eat: crustaceans, insect larvae, annelid worms
Feeding process:
Tentacles trap prey with the help of the nematocyst (encased in the cnidocyte)
Mouth widens (with the help of gland cells) to engulf prey
Extracellular digestion takes place in the GVC with the help of gland cells secreting digestive enzymes
Food particles go into nutritive-muscular cells for further intracellular digestion

60. Glutathione
A chemical activator that triggers the feeding process of certain cnidarians
Cause the tentacles to move more
Causes the hydra to be more alert
Causes the gland cells to release lubricant and widen the mouth
Prepare for food intake

61. Hydra Reproduction Reproduce both sexually and asexually
Sexual Reproduction
Form temporary gonads in the fall
Eggs and sperm and are shed into the water and form fertilized eggs
Hydra will hatch in the spring (favorable environment)
Asexual Reproduction
Budding: starts as a growth on the side of the “parent” hydra
Eventually will detach from parent and live on its own

62. Hydra Budding

63. Obelia- Hydroid colony
2nd example of Hydrozoan class
Has a polyp and medusa stage in its life cycle
All polyps in the colony are usually interconnected
Contains a base, stalk and terminal zooids
Zooid: general term for an individual polyp animal in a colonial cnidaria

64. Obelia Structure
Hydrorhiza: (root-like) base that attaches the colonial polyp to a substrate
Hydrocauli: (stem) part that extends from the hydrorhiza and the individual zooids
Zooid: attached to the hydrocaulus; individual polyp animals

65. Obelia Structure

66. Types of tissue found in the Obelia
Coenosarc: the inner, living, cellular part of the Obelia
Perisarc: the outer, protective, non-living, covering of the Obelia
Made of chitin

67. Obelia Structure

68. Types of Zooids Gastrozooids Also called hydranths
Feeding animals of the colony
All have tentacles with cnidocytes
Feed on crustaceans, worms, and larvae
If one polyp eats it provides nutrients for the entire colony
Digestion and circulation of food is aided by ciliated nutritive muscular cells and body wall contractions

69. Types of Zooids Gonozooids Reproductive polyp that release medusa buds
Obelia reproduces both sexually and asexually.
Sexual Reproduction: (most common pathway)
* young medusa leaves the colony
* medusa buds mature and shed gametes (sperm and egg)
* fertilization occurs
* Zygote created turns into a Planula (free swimming larvae stage) that swims and attaches to form new colony

70. Obelia Reproduction Asexual Reproduction:
Occurs by budding-> increases the size of the colony
Occurs but outgrowth of the body wall
Creates new gastro- and gono- zooids

72. Obelia Reproduction

74. Medusa structure of Obelia
“Jellyfish” form
Contains:
Velum: membrane under the surface if the umbrella of the medusa that projects inward
Contains tentacles with cnidocytes
Manubrium: tissue projecting from the oral side of the medusa; surrounds the mouth

75. Internal medusa structure of Obelia
Entire system is lined by the gastrodermis
Gastrovascular cavity is continuous from the mouth to the tentacles
Pathway of food flow: (disperses food w/o circulatory system)
Mouth-> opens to the manubrium projecting form the oral side of the mouth-> leads to the stomach and the 4 radial canals-> connects to the ring around the margin of the bell-> connects the tentacles

76. Movement of Obelia medusa
Aboral side first
Characterized by weak jet propulsion
Muscular pulsations fill bell with water and empty water to propel medusa

77. Obelia: Medusa Stage

78. Nerve Net of Obelia Medusa
Concentrated in 2 nerve rings at the base of velum
Composed of
Statocysts: functions in equilibrium
Ocelli: light sensitivity

79. Nerve Net

80. Physalia physalis Portuguese Man of War (PMOW)
3rd example of Hydrozoan class
Located in warmer, tropical waters
Considered to be a polymorphic swimming community that is composed of several types of animals that swim and act as 1 colony
Nematocysts are located all over the tentacles
Some are very dangerous-> secrete a neurotoxin

81. Structure of PMOW Pneumatophore Rainbow colored float Filled with gas
Carries future generations and acts as a nursing center
Can briefly deflate for protection

82. Types of individuals in a colony
Gastrozooids: feeding zooids that ingest the food
Dactylzooids: long fishing tentacles that sting, capture the prey and bring it to the mouth
On average are 30 feet long (can be as long as 165 feet underwater)
Covered in nematocysts
Gonozooids: sacs with ovaries and testes
Function in reproduction

83. Portuguese Man 0’ War
Tentacles of Physalia physalis