1. Marine Invertebrate Zoology
The Hydrostatic Skeleton
Phylum Cnidaria
Whenever we think of a skeleton we think of bones in a doctor’s office
But if movement is going to be accomplished we must have a skeleton
Invertebrates use a hard exoskeleton or a fluid filled hydrostatic skeleton
Phylum Cnidaria

2. The Hydrostatic Skeleton
A solid or fluid system permitting muscles to be stretched back to their original length following a contraction. May or may not have a protective or supportive function as well
Invertebrates commonly use a hydrostatic skeleton since they are getting support from the environment
Phylum Cnidaria

3. The Hydrostatic Skeleton
The hydrostatic skeleton requires:
A muscle can shorten and relax, but it can not actively extend itself
Example of biceps and triceps contracting and relaxing on your arm (antagonize movement) vertebrates in the terrestrial environment have a rigid skeleton for support in a non-supportive environment
The hydrostatic skeleton requires:
Presence of a cavity with an incompressible fluid that transmits pressure changes uniformly in all directions
The cavity is surrounded by a flexible outer membrane, permitting deformations of the outer body wall and
2 different muscles that orientates in different directions
The volume of fluid in the cavity remains constant
Phylum Cnidaria

4. Phylum Cnidaria Overview
Defining Characteristics
Formation of complex intracellular organelles called nematocysts
Planula larvae in the life cycle
The phylum is composed of anemones, corals, sea whips, hydroids, and jellyfishes
Diploblastic
Phylum Cnidaria
Overview
Defining Characteristics
Secretion of complex intracellular organelles called nematocysts
used in prey capture and defense can be quite painful and even life threatening
Planula larvae in the life cycle (ciliated, mouth less larvae, this is the sexual stage of the life cycle)
The phylum is composed of anemones, corals, sea whips, hydroids, and jellyfishes
looking at a coral and jellyfish the casual observer finds it hard to believe that they are related
you will have a better appreciation for this classification after our discussion
Slightly more complex than Porifera but still has limited organ development
For all members of the phylum the body consists of two living cell layers (diploblastic): the epidermis and the gastrodermis
We have called these layer ectoderm and endoderm in previous lectures, this high lights nomenclature problems in science
Used to be called coelenterata (hollow gut) and was classified along with the sponges and ctenophores
have remarkable similarities to the comb jellies but there are significant differences which we will discuss later
Over 11,000 species in the world over 60 shallow water species in our area
Mostly Marine, Radially symmetrical
Phylum Cnidaria

5. Diploblastic Animals Epidermis Gastrodermis Phylum Cnidaria
Mesoglea = jelly which can range from thick and fibrous to almost absent non-living, but may contain living cells for digestion etc.
Epidermis = which can excrete a cuticle or exoskeleton
Gastrodermis = secretory for digestion, ciliated for circulation, folded for absorption
Gastrovascular cavity = functions as digestion, absorption and circulation for some species it acts as a fluid skeleton
Gives the advantage to handle a wide array of food items
In most cases the mouth and digestive cavity wall is surrounded by nematocysts and opens into the gastrovascular cavity
Phylum Cnidaria

6. Nematocysts Used for gathering food or defense
Produced in special cells called cnidoblasts
Stinging cells (Nematocysts or cnidae)
The phylum is characterized by these structures
Used for gathering food or defense (over 30 different types have been described)
some are used for sticking to things, tangling things, penetration of the skin, or the secretion of powerful proteinaceous toxins
Nematocysts
Produced in special cells called cnidoblasts
Can be produced in the area of use or in other locales and then moved to the area of need
SEM micrograph of nematocysts penetrating skin
Phylum Cnidaria

7. Nematocysts Consist of a capsule that is occluded by an operculum
Barbs are usually located near the surface of the cnidoblast
Discharge with an explosive force that takes less than 3ms.
Cnidocil = trigger that projects form the tip of an undischarged nematocysts
Consist of a capsule that is occluded by an operculum
Barbs are usually located near the surface of the cnidoblast
Discharge with an explosive force that takes less than 3ms.
Cnidocil = trigger that projects form the tip of an undischarged nematocysts
Triggered by tactile or chemical cues
Once discharged it can not be used again
Phylum Cnidaria

8. Nematocysts Phylum Cnidaria
Consists of a capsule that is occluded by an operculum
Barbs are usually located near the surface of the cnidocyte
Discharge with an explosive force and takes >3ms.
Cnidocil = trigger that projects form the tip of an undischarged nematocysts
Triggered by tactile or chemical cues
Once it is discharged it can not be used again
Usually >50m impressive in the number per square inch
Astomocnidae = closed end threads that are used for attachment and lasso prey
Stomocnidae = open end thread used for penetration and the injection of toxins
Abundant on tentacles of all species and the digestive cavity of some species
cnidae capsules average 50 microns in size and rarely reach 100 microns
they are significant due to the great number per square mm
#143 Jellyfish types and sting treatment
Blue Planet Coral seas (Chapter 2, 3, and 11)
Phylum Cnidaria

9. Cnidarian Nutrition
A major cnidarian drawback is the absence of an anus
Carnivorous feeders on zooplankton and small fish
Reef building corals also depend on symbiotic photosynthetic dinoflagellates for energy
Nutrition
For those contemplating reincarnation as a cnidarian a major drawback is the absence of an anus (not particularly appealing)
This disadvantageous because the animal must expel the remains of one meal before consuming another
also movement can result in the expulsion of food material before digestion
Carnivorous feeding on zooplankton and small fish
Reef building corals (hermatypic) also depend on symbiotic photosynthetic algae for energy (some other species depend on algae as well)
Nematocysts are discharged and then brought to the mouth
Mucus secreting cells aid in digestion
In the gastrovascular cavity enzymatic glands reduce contents to soupy broth
Products of digestion are circulated by cellular diffusion
Phylum Cnidaria

10. Reproduction and Nervous System
Reproduce asexually and sexually
Larvae - mouthless, ciliated, swimming planula
In the classes Scyphozoa and Hydrozoan the sexual stage is the medusa
Alternate between the polyp and medusa
The polyp asexually produces a medusa that sexually produces a planula larvae, which then settles into a polyp
Polymorphism = more than one stage per species
Nervous system
In contrast to Porifera cnidarians do posses a nervous system
Nerve cells are arranged in an irregular nerve net or plexus (lacks a central nervous sys.)
With the initiation of a signal it spreads to muscle and sensory cells
Gas exchange and Excretion
Lack gills and other specialized respiratory structures Occurs across the general body surface
Nitrogenous waste (ammonia) also diffuses
Reproduction
Reproduce by asexual reproduction
Sexual reproduction - Larvae = mouthless, ciliated, swimming planula (romer)
In the classes Anthozoa sexual stage is the polyp, medusa is absent
In the classes Scyphozoa sexual stage is the medusa, Alternate between the polyp and medusa generations
The polyp asexually produces a medusa that sexually produces a planula larvae, which then settles into a polyp
Hydrozoa is a combination of the two
Polymorphism = more than one stage per species
Promotes diversity of habitat distribution big advantage
Phylum Cnidaria

11. Polyp & Medusa

12. Polyp and Medusa Medusa (jellyfish) Usually solitary and free swimming
The mouth and tentacles are directed downwards
Contains thick mesoglea
Polyp (tube shape)
Solitary or colonial, usually sessile attached by its base
Mouth and tentacles are pointed upward
Mesoglea is usually thin
May have a fluid skeleton or calcium carbonate exoskeleton
The phylum contains two body forms:
Medusa (jellyfish)
Usually solitary and free swimming
The mouth and tentacles are directed downwards
Contains thick mesoglea
The gastrovascular cavity has a digestive chamber with circulatory canals radiating from it
Polyp (tube shape)
Solitary or colonial, usually sessile which is attached by its base
Mouth and tentacles are pointed upward
Mesoglea is usually thin
May have a fluid skeleton or calcium carbonate exoskeleton
Phylum Cnidaria

13. Cnidarian Classification
Phylum Cnidaria
Class Scyphozoa
Class Cubozoa
Class Hydrozoa
Order Hydroida
Order Siphonophora
Class Anthozoa
Subclass Alcyonaria (Octocorallia)
Subclass Zoantharia (Hexacorallia)
Classification
Phylum Cnidaria (G: a stinging thread (G: hollow gut))
Class Scyphozoa (G: cup animals)
Class Cubozoa (G: cube animals)
Class Hydrozoa (G: water animals)
Order Hydroida
Order Siphonophora
Class Anthozoa (G: flower animals)
Subclass Alcyonaria (Octocorallia)
Subclass Zoantharia (Hexacorallia)
Phylum Cnidaria

14. Class Scyphozoa Defining characteristic
Asexual replication by strobilation
Includes the true jellies, moon jellies (Aurelia) and Sea Nettles (Chrysaora)
Scyphozoa (cuplike animals) 200 species
Defining characteristic
Asexual replication with strobilation
Includes the true jellies, moon jellies (Aurelia) and Sea Nettles (Chrysaora)
This class is dominated by a large medusa stage (2-40cm)
can be up to 2meters in width
Mesoglea is thick and gelatinous giving it the name jellyfish
#379 Audubon
There are blooms that are occurring throughout the world
In 2000 there was an immense bloom have effects on the ecosystem
Some areas of the Chesapeake are not swimmable
A decade ago the black sea anchovy fishery was devastated by Mnemiopsis
Phylum Cnidaria

15. Scyphomedusa Structure
Contains a large swimming bell that has tentacles and sensory capsules
Rhopalia
Statocysts
Ocelli
Medusa Structure
Similar to hydroid medusa
Contains a large swimming bell that has tentacles and sensory capsule
Located along the margin (rhopalia) contains ocelli and statocysts
Rhopalia = sensory organ which senses light, odor, and position
Pacemaker which controls muscle contractions
Rhopalia
Phylum Cnidaria

16. Medusa Movement Phylum Cnidaria
Movement is accomplished by a contraction forcing water out of the area under the bell
The mesoglea plays an important part in the efficiency of swimming
the elasticity of the mesoglea gives the ability for it to pop back to its original shape
Phylum Cnidaria

17. Scyphomedusa Structure
Manubrium is elongated into 4 oral arms that hang from the subumbrella and catch food (not to be confused with the tentacles)
some have a manubrium instead of oral arms
Tentacles are located around the margin can be long or short
The coelenteron consist of 4 or more major radial canals and a marginal ring canal
Radial canals radiate from the central stomach to a ring canal, which encircles the bell
The radial and ring canals are the circulatory system
4 mesenteries or septa partition the stomach
This forms 4 gastric pockets
The inner septa have gastric filaments, which have stinging cells to subdue swallowed prey
Phylum Cnidaria

18. Scyphozoa Reproduction
Individuals are dioecious
Fertilized eggs develop into a planula larvae
Settles on a firm surface in a quiet place and forms a polyp
These reproduce asexually and bud off seasonally; strobila or strobilaton
Phylum Cnidaria

19. Scyphozoa Lifecycle Gonad development occurs in each septum
The radial and ring canals are the circulatory system
Life cycle Figure
The individual releases either male or female gametes from the mouth
Gonochoristic or dioecious (G: two houses)
Fertilized eggs = planula larvae
Settles on a firm surface in a quiet place and form a polyp (scyphistoma)
Same structure as the hydroids usually much smaller
These reproduce asexually and bud off seasonally (strobila or strobilaton)
Each breaks away and forms a swimming ephyra which grows into a medusa
Individuals are usually predators or suspension feeders. All are marine
Order Semaeostomeae
Common spp. Aurelia (moon jelly), Chrysaora (Sea Nettle), Cyanea (Lion’s Mane)
Order Rhizostomeae
Common spp. Stomolophus (Cannonball)
Eaten by sunfish, sea turtles, and spade fish
Blue Planet Seasonal seas (Chapter 3, 4)

20. Class Cubozoa Defining characteristics
Medusa with box-like body
Chiropsalmus quadrumanus (Sea Wasp)
Cubozoa (cube animals)
Defining characteristics
Medusa with box-like body
Rhopalia bear complex, lensed eyes
in addition to ocelli they also have eyes with lenses
among the most complex in the invertebrates
Cubomedusae are Jellyfishes with cubical transparent bodies
Common in Australia can die from the sting
(Box jellies)
Each individual bears 4 tentacles
The box curves inwards allowing for excellent swimming
similar to restricting a garden hose
#159 box jelly article (Chironex fleckeri)
more people die from theses stings than sharks
#379 Audubon
venom
Phylum Cnidaria

21. Class Cubozoa
Known as box jellies or sea wasps due to shape and painful sting
Occur in tropical and warm temperate seas
Does not reproduce through strobilation
Planula forms more polyps each of which develops into a medusa
Known as box jellies or sea wasps due to shape and painful sting
Occur in tropical and warm temperate seas
Chiropsalmus quadrumanus (Sea Wasp)
An animal 2-3cm long can have tentacles up to 30cm long
virulent nematocysts give them the ability to kill animals much larger than themselves
Cubozoa Eyes
Phylum Cnidaria

22. Class Hydrozoa
Due too small sizes and plant-like appearance people are unaware of their existence
Display both polyp and medusa in the life cycle
Mesoglea is thin or absent
Hydrozoa (water animals)
2700 species, due too small sizes and plant-like appearance people are unaware of their existence
Display both polyp and medusa in the life cycle
3 characteristics unite this class:
Mesoglea is never cellular
Gastrodermis lacks nematocysts
Gonads are epidermal (egg and sperm are shed directly to the outside)
Phylum Cnidaria

23. Hydroid Structure Polyps can be solitary or colonial
Very drab in appearance, no external skeleton, colonies are polymorphic
Hydroid Structure
Polyps can be solitary or colonial (more common)
In colonial forms the epidermis, mesoglea, and gastrodermis are continuous
Most colonies are cm in height
Very drab in appearance, no external skeleton, colonies are polymorphic
Hydra
Phylum Cnidaria

24. Polymorphism Hydroid colonies have polyps of different functions
Feeding - gastrozooids
Defense - dactylozooids
Reproduction - gonozooids
Hydroid colonies have polyps of different functions
Feeding (gastrozooids), defense (dactylozooids), reproduction (gonozooids)
Some harbor unicellular green algae (zoochlorellae) for a mutualistic relationship
Phylum Cnidaria

25. Hydromedusa Structure
Medusoid Structure
Medusa is similar to Scyphozoa jellyfish Medusa
Exumbrella - upper surface
Subumbrella - lower surface
Smaller (.5cm-6cm) and have a velum (jet water)
Mouth hangs at the end of the manubrium (tube) has cnidocytes
Mesoglea is thick but acellular
Tentacles hang off the bell margin
Margin also contains:
Ocelli: photoreceptor, which contains pigment
Statocysts: pace makers and balance sensors for contractions
Phylum Cnidaria

26. Hydrozoan Reproduction
Hydroid stage can reproduce by asexual budding
Eventually the bud detaches and becomes independent
Also has considerable powers of regeneration
Gonozooids will release medusa
All medusa reproduce sexually
Reproduction
Hydroid stage can reproduce by asexual budding
Eventually the bud detaches and becomes independent
Also has considerable powers of regeneration
Turning the polyp inside out experiment
Some release medusa others do not
When medusa is not released a planula larva is created by the attached, reduced medusa stage
All medusa reproduce sexually
Phylum Cnidaria

27. Hydrozoa Lifecycle
Fertilization may occur in the water, on the manubrium or internally
Planula = free swimming (hours - days) larva that settles and develops into a hydroid colony
The appearance of hydroid medusa is highly seasonal and related to water temperature
Can sting and cause rashes
A 7cm colony can release 4450 medusa over 3 days
Life span of medusa can range from a few days to months

28. Order Hydroida
Most species of the class hydrozoa in our area are hydroids
Form sessile colonies of polyps and are usually mistaken as seaweed
Exceptions are Velella and Porpita = hydroids that float freely at the surface
Order Hydroida
Most species of the phylum hydrozoa in our area are hydroids
Form sessile colonies of polyps and are usually mistaken as seaweed
Produce microscopic, transparent swimming Medusa
Exceptions are Velella and Porpita = hydroids that float freely at the surface
Velella
Phylum Cnidaria

29. Order Siphonophora Swimming or floating hydrozoan colonies
Portuguese man-o-war (Physalia physalis)
Order Siphonophora
Swimming or floating hydrozoan colonies
Portuguese man-o-war (Physalia physalis)
Dactylzooids capture and kill prey
Float = (pneumatophore) is a modified medusa
Other Siphonophora have swimming bells that resemble typical medusa but lack a mouth, tentacles and sensory organs.
Never release sexual medusa and all but Physalia are hermaphrodites
Phylum Cnidaria

30. Phylum Cnidaria More Siphonophora = Nectalia sp. = Muggiaea sp.
All use the nectophore as a method for propulsion
Phylum Cnidaria

31. Class Anthozoa Defining characteristics
Absence of a medusa stage
Anemones, corals, sea whips, sea pansies
Polyps consists of a column, flattened oral disk surrounding the mouth which bears tentacles
Some polyps are solitary (anemones) others are colonial (coral)
Anthozoa
Defining characteristics
Absence of a medusa stage
Coelenteron is partitioned by distinct sheets of tissue (septa)
Anemones, corals, sea whips, sea pansies, 6000 species (70% of all described)
Medusa stage is absent
Brings up some interesting evolutionary questions
Was the cnidarian a polyp shaped animal that evolved a medusa?
Polyps consists of a column, flattened oral disk surrounding the mouth which bears tentacles
Some polyps are solitary (anemones) others are colonial (coral)
Phylum Cnidaria

32. Class Anthozoa Feed using tentacles that move food to the mouth
Water is used by some as a fluid skeleton
Produce planula larvae that settle and form new colonies
Can also reproduce using pedal laceration and fission
Feed using tentacles that move food to the mouth
The mouth opens into the pharynx (cilia pump water into the gastrovascular cavity, which can fill deflated polyps).
Vertical sheets of mesenteries partition gastrovascular cavity
Feeding polyps often have mesenteries, which are lined with stinging cells to subdue prey
When Anthozoans retract water is expelled through the mouth
Water is used by some as a fluid skeleton
Also have acontia that can be used for defense, loaded with nematocysts
Produce planula larvae that settle and form new colonies
Can also reproduce using pedal laceration and fission
#247 How corals feed
a colony can consume 19% of its daily energy requirement in 2 hours after dark
Blue Planet Coral seas (Chapter 2, and 3)
Phylum Cnidaria

33. Subclass Zoantharia (Hexacorallia)
Posses 6 septa that separate the gastrovascular cavity
Many species are solitary and lack a protective covering (sea anemones)
Separated into two major orders
Subclass Hexacorallia
Posses 6 septa that separate the gastrovascular cavity
Many species are solitary and lack a protective covering (sea anemones)
Separated into 2 major orders:
Order Actiniaria
Sea anemones
Order Scleractinia
Stony Corals
Phylum Cnidaria

34. Sea Anemones Solitary and lack a rigid skeleton
Have a broad adherent pedal disk
Can reproduce asexually (pedal laceration) and sexually
Order Actiniaria
Sea anemones, solitary and lack a rigid skeleton
Have a broad adherent pedal disk
Can reproduce asexually (pedal laceration) and sexually
Eggs can be fertilized in the gastrovascular cavity or in the water
Larva then settles and grows tentacles
Others in this group include the:
Phylum Cnidaria

35. Stony corals
Colonial with calcium carbonate skeleton secreted by the epidermis
May be reef-building (hermatypic) or non reef building (ahermatypic)
Hermatypic corals live in warm clear waters and can form chains around islands
Zooxanthellae forms a symbiotic relationship with coral
Order Scleractinia (stony corals)
Colonial with calcium carbonate skeleton secreted by the epidermis
Each polyp has a depression, which it occupies
Radial partitions result from calcium carbonate deposition on the mesenteries
Some species are reef builders and may harbor zooxanthellae
Feeds mostly on zooplankton, usually at night
Expands by asexual budding or sexual planula similar to anemone
May be reef-building (hermatypic) or not (ahermatypic)
Hermatypic corals live in warm clear waters and can form chains of islands
The Great Barrier reef is 2000 km. Long (Disscus problems facing corals)
Scientific american (#66) Coral bleaching, #249 Deep water corals ahermatypic
#316 Nature reef bleaching outbreak
Tropical water is poor in plankton and corals are carnivorous
Zooxanthellae forms a symbiotic relationship with coral
Coral gets energy and zooxanthellae gets protection and waste products
Blue Planet the deep (Chapter 8)
Corals are also important in medicine today for both bone graphs (face and jaw) and artificial eye implants
Their system of appropriately sized interconnected pores is rapidly infiltrated by human blood capillaries and quickly incorporated into tissue
Phylum Cnidaria

38. Subclass Alcyonaria (Octocorallia)
Distinguishing characteristics
Sea whips, sea fans, and sea pansies are in this group
Can harbor zooxanthellae
Sub Class Alcyonaria (Octocorallia)
Distinguishing characteristics
Polyps have 8 septa that divided the gastrovascular cavity
Always have eight tentacles which posse side branches, like a feather
Sea whips, sea fans, and sea pansies are in this group
Can harbor zooxanthellae
Discuss research box on the palatability of coral spicules, and its importance as a defense mechanism
Phylum Cnidaria