Cnidarian Diversity

Classes of Cnidaria

• Anthozoa– Anemones and most corals

• Scyphozoa– Jellyfish

• Hydrozoa– Hydroids such as Hydra

• Cubozoa– Cube jellies

Cnidarian Classes

Anthozoa

Cubozoa

Scyphozoa Hydrozoa

Class:

Hydrozoa

Hydrozoans

• Large class with about 3,000 species

• Life cycle– Has both polyps and medusae

• Medusae usually solitary, small– Polyps predominate the life cycle

• Polyps usually colonial

• Habitat– Mostly marine– A few freshwater

sperm

Young polyp

male

female

Budding Hydra

Asexual

Sexualegg

Obelia - living

Order Siphonophorae

Siphonophores

Siphonophores

• Order of carnivorous colonial hydrozoans• About 175 species known

– Most live in deep ocean, so more are being discovered as deep dive capabilities improve

• Most are active swimmers• Typically elongate and rope-like,

– some reach lengths of 40 meters or more

• Gelatinous and most disintegrate when sampled with nets.

Siphonophores

• Siphonophores have elaborated on coloniality– Unique form of individuality that has led many

scientists to call them ‘superorganisms’.

• Colonial animals consisting of many multicellular individuals called zooids (zoh – ids) that are each homologous to solitary free-living organisms.– Zooids within a colony are all derived from the

same embryo and are genetically identical

Siphonophores

• Add new zooids through asexual reproduction, such as budding or fission– Not followed by physical separation.– Zooids remain attached and physiologically integrated. – There can be a dozen or more functional classes of

zooids in siphonophore colonies• arranged in precise species-specific patterns. • pattern is usually reiterated along a linear stem, • exact same sequence of specialized zooids

repeated

Siphonophores• Importance of siphonophore colonial structure

– The division labor between siphonophore zooids parallels the evolution of functional specialization at other levels of biological organization

• Between cells in a multicellular organism• Between casts in eusocial insects.

– Wide interest in evolution and developmental mechanisms involved in this division of labor

• Recognition of self from non-self• Germ line segregation during development• Selection within organism – selection of cancer cell lines

Barrel eye Fish – kleptoparasite of siphonophores

Macropinna microstoma

Physalia physalis

Physalia physalis

• Portuguese Man of War– Hydrozoan– Colony of many specialized polyps– Deadly sting even when dead on

the beach– Has symbiotic fish

• Nomeus gronovii (juveniles)– Feed on Physalia tentacles

and gonads , and may feed on other jellyfish

Nomeus gronoviiNomeus gronovii

Physalia physalis• The PortugueseMan-o’-War consists of four main

types of polyp. – A single polyp forms the large gas-filled float that sits on

the ocean surface and acts as a sail. – Other polyp types specialise as feeding tentacles

(gastrozooids, of which there are three types), – as defensive or prey-capturing tentacles (dactylozooids)

and • Hang to a depth of up to 40 meter, • Deliver a powerful sting.

– as reproductive organs (gonozooids).

Feeding Polyp

Mouth

The Portuguese man-o’war, Physalia physalis, is one of around 175 species in the order siphonophores, class Hydrozoa. It is not a typical member of the group. While Physalia drifts on the surface, blown by winds and carried by currents, most siphonophores are active swimmers and live beneath the surface. A few – the rhodaliid family – spend their lives tethered by their tentacles to the sea bottom. Because of their habitat and their fragility, siphonophores are extremely difficult to collect, and relatively little is known about them.

First Aid for Physalia Stings• Do not rub the sting area. • Remove any adhering tentacles. • Rinse the area well with sea water (not freshwater).

– NO VINEGAR – can cause more envenomation by a newly discovered species of Physalia

• Place the stung area in hot water - no hotter than can be comfortably tolerated.

• If the pain is unrelieved by heat, or if hot water is not available, apply ice packs.

• Send for medical aid if symptoms persist or worsen.

Glaucus atlanticus

Glaucus atlanticus

Vellela – By the Wind SailorOrder: Condrophora

VellelaNote: pneumatophore divided into multiple chambers. Only one gastrozooid, multiple gonozooids.

Commensal Hydrozoan, Hydractinia echinata, on shell of hermit crab. Some zooids modified into spines

First Aid for Physalia Stings• Do not rub the sting area. • Remove any adhering tentacles. • Rinse the area well with sea water (not freshwater).

– NO VINEGAR – can cause more envenomation by a newly discovered species of Physalia

• Place the stung area in hot water - no hotter than can be comfortably tolerated.

• If the pain is unrelieved by heat, or if hot water is not available, apply ice packs.

• Send for medical aid if symptoms persist or worsen.

Scyphozoa• Jellyfish

• Medusa is dominant life history stage

• Active swimmers– Contract muscles

• Causes water to shoot out from bell• Mesoglea deforms• Propels animal forward

– When muscles relax mesoglea pops back to normal shape• Pulls animal downward• So net forward movement is due to rapid speed of bell

contraction

Scyphozoa

• Feeding– Food captured by nematocysts– Passed to mouth and through manubrium to

the four gastric pouches (coelenteron)– Partial digestion occurs in these pouches – Ciliated canals distribute partly digested food– Particles are phagocytized and rest of

digestion is intracellular

Aurelia medusa

Scyphozoan Anatomy

• Coelenteron (central blind sac) = gastrovascular cavity

• Body wall composed of two epithelia– outer epidermis – inner gastrodermis

• Mesoglea (gelatinous connective layer) lies between the two epithelia.

Aboral surface = exumbrella

Oral surface = subumbrella

Scyphozoan Anatomy

• Mouth opens at one end of the coelenteron and marks the oral end – usually surrounded by one or more circles of tentacles

• Manubrium is a stalk that elevates the mouth above the oral surface

• The opposite pole is the aboral surface. – Imaginary line connecting the oral and aboral poles is

the axis of symmetry– radial symmetry of the body is organized this axis

Adradial canals

Perradial canals

& manubrium

Aboral surface is concave and resembles a large sucker. This suction assists the animal in maintaining contact with the substratum. With it the jellyfish can remain in place on smooth vertical surfaces as you have observed in the aquarium.

Cassiopeia - Upside Down Jellyfish

• Note purple vesicular appendages– flattened, elongate, club-

shaped – May be distally birfurcated – Many sizes– Open into the brachial

canals• Number, size, and color vary

with sex and age• Function is not well

understood.

Cassiopeia• These animals inhabit shallow, quiet, sunlit,

tropical, marine waters, usually on soft bottoms – often found in shallow waters around the margins

of magrove beds ex. South Florida

Cassiopeia

• Contain large numbers of zooxanthellae – Can exist, and even grow,

utilizing photosynthate as its sole source of nutrition

– Also can feed on small zooplankton via secondary mouths

– Animals in aquarium seem to be shrinking possibly because light isn’t bright enough

Oral arms

Brachial canal

Secondary mouths

Oral arms

Cassiopeia• Vesicular appendages are hollow, blind sacs

– lumen is continuous with that of the brachial canal to which it is attached.

• The interior of each large vesicle may be purple, sometimes colorless, bluish, or bluegreen. – The inner epithelium of the appendages is gastrodermis

and bears numerous small, nearly spherical nematocytes and zooxanthellae

• The vesicles are used in trapping small crustaceans such as copepods and amphipods which are then stung to death.

Cassiopeia• Vesicular appendages also provide surface area

for the deployment of zooxanthellae in the sunlight.

• May also help camouflage the jelly in grass beds. • Small clusters of nematocysts on their outer

surface break easily from the vesicle and presumably discourage predators. – Disturbed jellies fill the nearby water with these

nematocysts which may then sting nearby predators or even swimmers.

Scyphozoa

• Circulation– Gases exchanges by diffusion as water

circulates through canals

• Life Cycle – see slides– Alternation of generations

• Medusa: dominant form• Polyp

– What’s a ramet? What’s a genet?

Aurelia medusa

scyphistoma

strobilum

ephyra

planula

Freshwater Jellyfish

• The freshwater jellyfish found in Wisconsin are one of several species of Craspedacusta native to China. – Two species (C. sowerbii and C. sinensis) live

in the Yangtze River, the world's third longest river.

• Freshwater jellyfish were first reported in North America as early as 1884.

• Sightings in Wisconsin date to 1969.

CraspedacustaCraspedacusta sowerbiisowerbii

• Probably evolved from Probably evolved from estuarine species, but estuarine species, but almost nothing is known almost nothing is known about the evolution of about the evolution of freshwater jellyfish.freshwater jellyfish.

Life History

• Stages– Egg– 2 kinds of larvae – Polyp– Medusa

• A cyst stage also forms.

Life History

• Both polyps and medusae feed on zooplankton.

– The polyps, hardly more than 1/8th –inch long, eat protozoans, rotifers, copepods, and water fleas.

– The medusae, about one inch across, can use their tentacles to sting these same critters and capture even larger prey, such as water mites and midge larvae.

– Only rarely do they stun newly hatched fish fry.

Life History• In some years, especially during hot summers in

Wisconsin, the polyp colony produces medusa buds. Each of these top buds becomes either a male or female medusa. The developing medusa grows from nutrition supplied by the parent polyp.

• After a week or two, and still quite small, the medusa leaves home to become free swimming. Another five weeks are needed for the medusa to mature. When full grown, the medusa has a nearly transparent body called a bell that dangles long, hair like tentacles we all associate with jellyfish.

Asexual

Sexual

Life History

• Medusae live only a few weeks, release eggs, and die. The polyps can live from spring until fall, when they may roundup into cysts.

– Covered with a chitinous “skin” that encloses fairly dry cells, the cysts are able to survive drought and cold.

– In Wisconsin, the cysts survive on the bottoms of ice-covered ponds, lakes, and quiet river pools where the water is slightly above freezing.

– Cysts are also a dispersal stage for jellyfish to spread north of their home range and invade new waters.

Aequorea victoriaAequorea victoria

Bioluminescent jellyfish– produces green Bioluminescent jellyfish– produces green fluorescent protein Osamu Shimomura – Nobel fluorescent protein Osamu Shimomura – Nobel

Prize for GFPPrize for GFP

Cubozoans

Cubozoans

• Sea wasp or Box Jelly– Chironex fleckeri

• Deadliest venomous animal

Cubozoans

• Venom contains toxins that attack the heart, nervous system, and skin cells.

• Sting is so overpoweringly painful that human victims have been known to go into shock and drown or die of heart failure before even reaching shore.

• Survivors can experience considerable pain for weeks and often have significant scarring where the tentacles made contact.

Cubozoans

• Most box jellies are small – a few centimeters– Bell is square in cross section

• 4 tentacles or groups of tentacles at each corner– Tentacles can be 3 meters long– Each tentacle has about 5,000 stinging cells,

which are triggered not by touch but by the presence of a chemical on the outer layer of its prey.

Cubozoans

• Most highly derived cnidarians– Strong swimmers

• Have developed the ability to move rather than just drift,

• Move at up to four knots through the water.

– Highly developed nervous system• Complex, image forming eyes

Cubozoans

• Complex, image forming eyes– Grouped in clusters of six on the four sides of their

bell. – Each cluster includes a pair of eyes with a

sophisticated lens, retina, iris and cornea, although without a central nervous system

– Not sure how they process what they see.

Major Features of the Adult Cubozoan

complex eye with lens and iris

simple eye

Cubozoans

• Medusa is dominant life history stage• Fertilization is internal

– Male passes packets of sperm into bell of female

– Fertilized eggs produce planula larva

– Planulae settle after a few days and develop into polyps

• Polyps may form buds

• Each polyp and each bud will produce medusae

• During metamorphosis, the polyp tentacles are resorbed and four new tentacles and four rhopalia are formed.

• Phylogeny not completely understood– Left panel shows old idea– Right two panels show current hypotheses

• There is one order of cubozoans: Cubomedusae– Two families: Chirodropidae and Carybdeidae