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Biology 320Biology 320Invertebrate ZoologyInvertebrate Zoology
Fall 2005Fall 2005
Chapter 7 – Phylum CnidariaChapter 7 – Phylum Cnidaria
Phylum CnidariaPhylum Cnidaria Hydra, anemones, stony corals, Hydra, anemones, stony corals,
soft corals, hydroids, and soft corals, hydroids, and jellyfishesjellyfishes
All are marine (approx. 10,000 All are marine (approx. 10,000 spp.) or freshwater (approx. 20 spp.) or freshwater (approx. 20 spp.), with no terrestrial spp.spp.), with no terrestrial spp.
May be colonial or solitaryMay be colonial or solitary
Responsible for the building of Responsible for the building of coral reefs, which are rivaled in coral reefs, which are rivaled in diversity only by tropical diversity only by tropical rainforestsrainforests
Posses cnidocytes (cnid = nettle) Posses cnidocytes (cnid = nettle)
General Form and FunctionGeneral Form and Function
General body structure resembles a gastrulaGeneral body structure resembles a gastrula
Posses a cavity known as a coelenteron Posses a cavity known as a coelenteron (gastrovascular cavity)(gastrovascular cavity)
Have a mouth surrounded by tentaclesHave a mouth surrounded by tentacles
Radially symmetrical around an oral-aboral axisRadially symmetrical around an oral-aboral axis Useful because food, predators, etc. may approach Useful because food, predators, etc. may approach
from any anglefrom any angle
Display two body forms, often Display two body forms, often in one life-cyclein one life-cycle
PolypPolyp Resembles a flower and stemResembles a flower and stem
Has a pedal disc and an oral Has a pedal disc and an oral discdisc
Sessile and benthic, with a Sessile and benthic, with a “mouth-up” orientation“mouth-up” orientation
MedusaMedusa Umbrella or bell-shapedUmbrella or bell-shaped
Manubrium is more defined Manubrium is more defined and resembles an elephant’s and resembles an elephant’s trunk with a mouth at the endtrunk with a mouth at the end
““Mouth-down” orientationMouth-down” orientation
In general, the body wall In general, the body wall is composed of three is composed of three tissue layerstissue layers Epidermis - epitheliumEpidermis - epithelium
Gastrodermis – epitheliumGastrodermis – epithelium
Mesoglea (a gelatinous Mesoglea (a gelatinous ECM) – connective tissueECM) – connective tissue
Cnidarians are Cnidarians are diploblasticdiploblastic
Colonial CnidariansColonial Cnidarians Occurs when a juvenile Occurs when a juvenile
replicates via budding, replicates via budding, however, buds do not separatehowever, buds do not separate
Produces zooidsProduces zooids Means “tiny animal”Means “tiny animal” Pronounced “ZOE-oid”Pronounced “ZOE-oid” Resemble the juvenileResemble the juvenile
Preserves SA:Vol because Preserves SA:Vol because zooids are small and thus have zooids are small and thus have a large SA:Vola large SA:Vol
Predisposition to filter feedingPredisposition to filter feeding Multiple mouths and feeding Multiple mouths and feeding
appendagesappendages Broad distributionBroad distribution Small size Small size
Three main types of colonies, varying in Three main types of colonies, varying in complexitycomplexity Stolonate – posses stolonsStolonate – posses stolons Coenosarc – posses a coenosarc and soleniaCoenosarc – posses a coenosarc and solenia Fruticose – typically upright and branching Fruticose – typically upright and branching
with a plantlike / feathery appearancewith a plantlike / feathery appearance
Two types of buddingTwo types of budding Fixed-length – as found in Fixed-length – as found in ObeliaObelia Axial-polypAxial-polyp
Cnidarian SkeletonsCnidarian Skeletons
Exceeds the diversity of poriferan skeletonsExceeds the diversity of poriferan skeletons
Exoskeletons of:Exoskeletons of: Chitinous periderm – some hydrozoansChitinous periderm – some hydrozoans Calcium carbonate – stony coralsCalcium carbonate – stony corals Shell fragments covering the epidermis – some anemonesShell fragments covering the epidermis – some anemones
Endoskeletons of:Endoskeletons of: Fibers and spicules, similar to those of poriferans – soft coralsFibers and spicules, similar to those of poriferans – soft corals Columns of cells containing turgid vacuoles – some hydrozoansColumns of cells containing turgid vacuoles – some hydrozoans
Hydrostatic skeletons – Hydrostatic skeletons – HydraHydra, many anemones, many anemones
Musculature and MovementMusculature and Movement
Posses antagonistic sheets of musclePosses antagonistic sheets of muscle Circular smooth muscle – gastrodermisCircular smooth muscle – gastrodermis Longitudinal smooth muscle - epidermisLongitudinal smooth muscle - epidermis
Medusae posses coronal muscles, Medusae posses coronal muscles, encircling the subumbrella. These encircling the subumbrella. These muscles are antagonized by the elastic muscles are antagonized by the elastic mesogleamesoglea
Cnidarians perform a wide variety Cnidarians perform a wide variety of movementsof movements
Shortening, extending and bending in Shortening, extending and bending in polypspolyps
Constriction of bells in medusae Constriction of bells in medusae (facilitates swimming)(facilitates swimming)
Inch-worming and somersaulting in Inch-worming and somersaulting in polypspolyps
Movement of feeding appendages for Movement of feeding appendages for prey manipulationprey manipulation
Retraction of the subumbrella in polyps Retraction of the subumbrella in polyps and medusaeand medusae
Cnidarian Nervous SystemsCnidarian Nervous Systems Two nerve netsTwo nerve nets
Base of epidermisBase of epidermis Base of gastrodermisBase of gastrodermis
Nets are joined by nerve Nets are joined by nerve bridges that span mesogleabridges that span mesoglea Nerve impulses can travel any Nerve impulses can travel any
directiondirection Important because of radial Important because of radial
sensory structuressensory structures
Medusa posses nerve rings, Medusa posses nerve rings, musculature, ganglia, and musculature, ganglia, and sense organs around bellsense organs around bell StatocystsStatocysts OcelliOcelli ChemoreceptorsChemoreceptors MechanoreceptorsMechanoreceptors
CnidocytesCnidocytes
For prey capture and defenseFor prey capture and defense
Grasp terminology firstGrasp terminology first Cnidocytes (cells) posses cnida (fluid-filled capsule with tubule)Cnidocytes (cells) posses cnida (fluid-filled capsule with tubule)
CnidocyteCnidocyte CnidaCnida FunctionFunction
NematocyteNematocyte Nematocyst Sting / release toxins Nematocyst Sting / release toxins
SpirocyteSpirocyte Spirocyst Spirocyst Tubule contains sticky Tubule contains sticky threads used for threads used for
adhesionadhesion
Cnidocytes are fairly ubiquitousCnidocytes are fairly ubiquitous Throughout epidermisThroughout epidermis On tentaclesOn tentacles Often in gastrodermisOften in gastrodermis
Nematocyst firingNematocyst firing Tubule coiled in capsuleTubule coiled in capsule Triggered by a combination of Triggered by a combination of
chemical and mechanical cues chemical and mechanical cues from prey (rarely fires on from prey (rarely fires on accident)accident)
Cytoplasmic water rushes in and Cytoplasmic water rushes in and ejects tubuleejects tubule
Toxins (proteins) may interfere Toxins (proteins) may interfere with Nawith Na++/K/K++ pumps or degrade pumps or degrade cell membranescell membranes
Hydra discharges 25% of Hydra discharges 25% of nematocysts eating one brine nematocysts eating one brine shrimpshrimp Replaced in 24hr Replaced in 24hr
Nutrition and Internal TransportNutrition and Internal Transport Blind gut called coelenteron or Blind gut called coelenteron or
“gastrovascular cavity”“gastrovascular cavity”
Coelenteron may posses septa to Coelenteron may posses septa to increase SA for: increase SA for: DigestionDigestion AbsorptionAbsorption Gas exchangeGas exchange ExcretionExcretion ReproductionReproduction Hydrostatic skeletal supportHydrostatic skeletal support
Various canals in medusae, that Various canals in medusae, that radiate out from central stomachradiate out from central stomach Radial canalsRadial canals Ring canalsRing canals
In polyps and medusae, coelenteron In polyps and medusae, coelenteron typically branches into each tentacletypically branches into each tentacle
When prey is caught, mouth When prey is caught, mouth opens and tentacles stuff prey opens and tentacles stuff prey inin
Enzymes digest extracellularyEnzymes digest extracellulary
Gastrodermal cells absorb Gastrodermal cells absorb monomersmonomers
Larger particles are digested Larger particles are digested intracellularlyintracellularly
Slow process; may take several Slow process; may take several daysdays
Wastes ejected through mouthWastes ejected through mouth
Many spp. posses Many spp. posses photosynthetic photosynthetic endosymbiontsendosymbionts
May account for 90% of May account for 90% of nutrition in somenutrition in some
Often defined patterns of Often defined patterns of fluid circulation around fluid circulation around coelenteroncoelenteron Ciliated gastrodermisCiliated gastrodermis Muscular contractionsMuscular contractions
Gas and Waste ExchangeGas and Waste Exchange All gas exchange occurs All gas exchange occurs
across general body across general body surfacessurfaces TentaclesTentacles Body wallBody wall
Waste exchange (excretion) Waste exchange (excretion) occurs across body walloccurs across body wall Ammonia is primary waste Ammonia is primary waste
product (aqueous)product (aqueous) Marine animal physiology Marine animal physiology
does not require water does not require water conservationconservation
Terrestrial invertebrates Terrestrial invertebrates have many structural have many structural adaptations for conserving adaptations for conserving water during excretion (as water during excretion (as we will see later)we will see later)
General ReproductionGeneral Reproduction Amazing regeneratorsAmazing regenerators
Can lose oral end and regrow itCan lose oral end and regrow it Living anemones can fully recover from dissectionsLiving anemones can fully recover from dissections
Clonal reproduction is common among polyps, but is less common Clonal reproduction is common among polyps, but is less common in medusaein medusae
Sexual reproduction in mostSexual reproduction in most Some are monoecious Some are monoecious
(hermaphroditic)(hermaphroditic) Most are dioecious (separate Most are dioecious (separate
sexes)sexes)
Germ cells usually develop in Germ cells usually develop in gastrodermisgastrodermis
Gametes are exocytosed into Gametes are exocytosed into coelenteroncoelenteron Typically extruded = external Typically extruded = external
fertilizationfertilization Retained in some spp. = Retained in some spp. =
internal fertilizationinternal fertilization
Zygote typically develops into Zygote typically develops into planula (swimming larva) planula (swimming larva) Settles (aboral end down)Settles (aboral end down) Develops into a juvenile polyp Develops into a juvenile polyp
Class AnthozoaClass Anthozoa ““Flower animals”Flower animals”
Sea anemones, corals, Sea anemones, corals, sea fans, sea pens, etc.sea fans, sea pens, etc.
Largest class, at 6000 Largest class, at 6000 marine spp.marine spp.
Solitary or colonialSolitary or colonial
All lack medusa phase of All lack medusa phase of lifecyclelifecycle
Anthozoan Body FormAnthozoan Body Form Long pharynx attaching to Long pharynx attaching to
coelenteroncoelenteron
Many septa, 6-192 Many septa, 6-192 depending on size of depending on size of speciesspecies
Some posses acontiaSome posses acontia Stringy filaments that are Stringy filaments that are
attached near base of attached near base of septasepta
Heavily armedHeavily armed May spew from mouth in May spew from mouth in
anemone deflatesanemone deflates Stony corals lack these Stony corals lack these
structuresstructures
MusculatureMusculature Mostly epidermal and Mostly epidermal and
gastrodermal epitheliomuscular gastrodermal epitheliomuscular cellscells
Epidermal musculature controls Epidermal musculature controls tentacles and oral disctentacles and oral disc
Gastrodermal musculature Gastrodermal musculature controls body columncontrols body column
RetractionRetraction Controlled by longitudinal Controlled by longitudinal
septal muscles called septal muscles called retractorsretractors
Tentacles and oral disc are Tentacles and oral disc are deflated of coelenteric fluiddeflated of coelenteric fluid
Pulled inside body columnPulled inside body column
Mesogleal sphincter muscle Mesogleal sphincter muscle closes opening like a draw-closes opening like a draw-stringstring
Must remove coelenteric Must remove coelenteric water to retract. water to retract. Siphonoglyph cilia beat Siphonoglyph cilia beat inwards to pump water back inwards to pump water back inin
Diversity of Class AnthozoaDiversity of Class Anthozoa Subclass Zoantharia (Hexacorallia)Subclass Zoantharia (Hexacorallia)
Hexamarous symmetry (septa and Hexamarous symmetry (septa and tentacles in multiples of 6)tentacles in multiples of 6)
Order Actiniaria - anemonesOrder Actiniaria - anemones
Order Scleractinia – stony coralsOrder Scleractinia – stony corals
Subclass Alcyonaria (Octocorallia)Subclass Alcyonaria (Octocorallia) Octomerous symmetry (septa and Octomerous symmetry (septa and
tentacles in multiples of 8)tentacles in multiples of 8)
Order Stolonifera – organ - pipe coralsOrder Stolonifera – organ - pipe corals
Order Gorgonacea – sea fans, whips, Order Gorgonacea – sea fans, whips, and plumesand plumes
Order Pennatulacea – sea pens, Order Pennatulacea – sea pens, feathers, and pansiesfeathers, and pansies
Subclass Zoantharia, Order ActiniariaSubclass Zoantharia, Order Actiniaria Sea anemonesSea anemones
1350spp.1350spp.
Average sizeAverage size 1.5cm – 10cm long1.5cm – 10cm long 1cm – 5cm diameter1cm – 5cm diameter Largest are over a meter wide and a Largest are over a meter wide and a
meter tallmeter tall
Often brightly coloredOften brightly colored
Some have unique methods of Some have unique methods of locomotionlocomotion Burrowing via peristalsisBurrowing via peristalsis Walking on tentaclesWalking on tentacles Swimming by thrashing tentaclesSwimming by thrashing tentacles
Methods of nutritionMethods of nutrition CarnivoresCarnivores
Suspension feeding - Suspension feeding - secrete mucus, trap particles secrete mucus, trap particles on tentacles, and move to on tentacles, and move to mouthmouth
Photosynthate - may posses Photosynthate - may posses two sets of tentacles: false two sets of tentacles: false for photosynthesizing for photosynthesizing (exposed during day) and (exposed during day) and true (exposed during night)true (exposed during night)
Can reproduce asexually Can reproduce asexually via pedal lacerationvia pedal laceration
Gonads are located in Gonads are located in septa septa
Interesting ecological Interesting ecological relationshipsrelationships Hermit crabs will wear anemone Hermit crabs will wear anemone
on shell; will transfer to new on shell; will transfer to new shell if anemone doesn’t shell if anemone doesn’t transfer itselftransfer itself Anemone gets substrate, Anemone gets substrate,
transportation to food, transportation to food, protection from predators, and protection from predators, and access to matesaccess to mates
Crab gets camouflage, Crab gets camouflage, nematocyst protectionnematocyst protection
Clown fish has surface mucus Clown fish has surface mucus that lacks nematocyte-triggering that lacks nematocyte-triggering compoundscompounds Anemone gets food attracted by Anemone gets food attracted by
fish, and removal of sediment fish, and removal of sediment and necrotic tissueand necrotic tissue
Clownfish gets protection and Clownfish gets protection and food scraps food scraps
Subclass Zoantharia, Order ScleractiniaSubclass Zoantharia, Order Scleractinia
Stony coralsStony corals
3600 spp., closely related to 3600 spp., closely related to anemonesanemones
Secrete a CaCOSecrete a CaCO33 exoskeletonexoskeleton Can weigh tons Can weigh tons Produce cups known as Produce cups known as
corallites that they can corallites that they can retract intoretract into
Puffer fish are coral Puffer fish are coral specialistsspecialists
Most are colonial with polyps Most are colonial with polyps 1mm to 3mm in diameter1mm to 3mm in diameter
Coral can be very colorful Coral can be very colorful due to photosynthetic due to photosynthetic endosymbiontsendosymbionts
Algae are often released in Algae are often released in conjunction with gametesconjunction with gametes
Coral reefs are in dangerCoral reefs are in danger
Coral bleaching (algae Coral bleaching (algae partially or completely partially or completely expelled) may occur under expelled) may occur under stressful environmental stressful environmental conditionsconditions Incorrect light intensity Incorrect light intensity
(including UV)(including UV) SalinitySalinity Temperature (even 1Temperature (even 1°C)°C)
Subclass Alcyonaria, Order StoloniferaSubclass Alcyonaria, Order Stolonifera Most octocorallians are soft corals, and do not produce a CaCOMost octocorallians are soft corals, and do not produce a CaCO33 shell shell
Most lack nematocysts and produce noxious chemicals to deter predatorsMost lack nematocysts and produce noxious chemicals to deter predators
Most are more tolerant of environmental fluctuationsMost are more tolerant of environmental fluctuations
Organ – pipe corals are included in Order StoloniferaOrgan – pipe corals are included in Order Stolonifera
Subclass Alcyonaria, Order GorgonaceaSubclass Alcyonaria, Order Gorgonacea Plantlike sea whips, fans, and plumesPlantlike sea whips, fans, and plumes
Highly branchedHighly branched
Endoskeleton is an axial rod made of gorgonin (highly cross-linked Endoskeleton is an axial rod made of gorgonin (highly cross-linked collagen)collagen)
Subclass Alcyonaria, Order PennatulaceaSubclass Alcyonaria, Order Pennatulacea
Sea pens, feathers Sea pens, feathers and pansiesand pansies
MedusozoaMedusozoa
Medusa phase present in life cycleMedusa phase present in life cycle Planula Planula polyp polyp medusamedusa
Tetramerous (multiples of four) radial symmetryTetramerous (multiples of four) radial symmetry
Cnidae are all nematocystsCnidae are all nematocysts
Two major classesTwo major classes Scyphozoa – large jelliesScyphozoa – large jellies Hydrozoa – small jellies, Hydrozoa – small jellies, HydraHydra, and hydroids, and hydroids
Class Scyphozoa, Body FormClass Scyphozoa, Body Form 200 spp. of large jellies200 spp. of large jellies
Polyps are small and Polyps are small and funnel shapedfunnel shaped Known as scyphistomaeKnown as scyphistomae
Coelenteron is divided by Coelenteron is divided by four septafour septa
Also have four septal Also have four septal funnelsfunnels Circulate water to gonads Circulate water to gonads
in adultsin adults
Medusa bellsMedusa bells Typically 2-40cm in Typically 2-40cm in
diameterdiameter Some greater than 2mSome greater than 2m Some brightly coloredSome brightly colored
Manubrium is divided Manubrium is divided into four oral armsinto four oral arms
Tentacles are located Tentacles are located around the periphery around the periphery of the bellof the bell
Coelenteron is divided Coelenteron is divided into four gastric pockets into four gastric pockets by septaby septa
Four pairs of gonads in Four pairs of gonads in septasepta
Four septal funnelsFour septal funnels
Many have radial canals Many have radial canals and marginal canalsand marginal canals
Gastrodermal cilia Gastrodermal cilia circulates watercirculates water
Lappets – rounded lobes Lappets – rounded lobes of umbrellar marginof umbrellar margin
Rhopalia – sensory Rhopalia – sensory organs found in grooves organs found in grooves between lappetsbetween lappets StatocystStatocyst General mechanoreceptorGeneral mechanoreceptor Possibly a chemoreceptorPossibly a chemoreceptor Sometimes a Sometimes a
photoreceptorphotoreceptor
Jellies have a nerve net Jellies have a nerve net and nerve ringand nerve ring
Scyphozoan reproductionScyphozoan reproduction Scyphistomae undergo Scyphistomae undergo
asexual reproductionasexual reproduction
Differentiate into a strobila Differentiate into a strobila from which stacked from which stacked miniature medusae separate miniature medusae separate via transverse fissionvia transverse fission
Process is known as Process is known as strobilationstrobilation
Juvenile medusa are known Juvenile medusa are known as ephyraas ephyra
Adult medusae sexually Adult medusae sexually reproduce reproduce
Diversity of Class ScyphozoaDiversity of Class Scyphozoa
Five ordersFive orders
Semaeostomeae – Semaeostomeae – AureliaAureliaRhizostomeae - Rhizostomeae - StomolophusStomolophus
Order Cubomedusae - Order Cubomedusae - ChironexChironex Order Stauromedusae - Order Stauromedusae - HaliclystusHaliclystus
Order Coronatae - Order Coronatae - LinucheLinuche
Class HydrozoaClass Hydrozoa HydraHydra and hydroids and hydroids
Other examples: fire coral and Other examples: fire coral and Portuguese man of warPortuguese man of war
3000 spp. 3000 spp.
Mainly colonies consisting of Mainly colonies consisting of polyp zooids and medusa polyp zooids and medusa zooidszooids
Oftentimes, medusa form as Oftentimes, medusa form as buds, but fail to be liberated buds, but fail to be liberated from colonyfrom colony
HydraHydra lifecycle does not lifecycle does not include medusa phase include medusa phase
Hydrozoan Body PlansHydrozoan Body Plans
Two forms of polypsTwo forms of polyps Athecate (A form)Athecate (A form) Thecate (L form)Thecate (L form)
Zooids are usually 1mm, Zooids are usually 1mm, or less, in lengthor less, in length
Large SA:VolLarge SA:Vol
Lack gastrodermal septaLack gastrodermal septa
MedusaeMedusae Arise as lateral buds from Arise as lateral buds from
colony, rather than via colony, rather than via strobilationstrobilation
Many posses a velum, an Many posses a velum, an iris diaphragm on iris diaphragm on subumbrellar margin that subumbrellar margin that aids in swimmingaids in swimming
ColoniesColonies Sessile, benthic, colonies Sessile, benthic, colonies
are called hydroidsare called hydroids Typically resemble plants Typically resemble plants
or seaweedsor seaweeds May be any of the three May be any of the three
colony forms (stolonate, colony forms (stolonate, coenosarcal, or fruticose)coenosarcal, or fruticose)
A-form coloniesA-form colonies Athecate – lack Athecate – lack
a theca a theca (extension of (extension of the periderm the periderm that acts as that acts as protective cup)protective cup)
Periderm ends Periderm ends at attachment at attachment point of zooidspoint of zooids
Typically grow Typically grow via axial-polyp via axial-polyp buddingbudding
L-form coloniesL-form colonies Periderm forms a Periderm forms a
wine-glass shape wine-glass shape thecatheca
Hydranth (water – Hydranth (water – flower) may flower) may retract into thecaretract into theca
Theca may have a Theca may have a hinged lid hinged lid (operculum)(operculum)
Grow via fixed-Grow via fixed-length buddinglength budding
Zooid TerminologyZooid Terminology
Can be a bit confusing, so spend some time with thisCan be a bit confusing, so spend some time with this
Monomorphic coloniesMonomorphic colonies Only consist of gastrozooids (feeding hydranths)Only consist of gastrozooids (feeding hydranths) Reproduce by releasing medusa budsReproduce by releasing medusa buds
Polymorphic coloniesPolymorphic colonies Posses other types of zooids, in conjunction with gastrozooidsPosses other types of zooids, in conjunction with gastrozooids Gonozooids – modified gastrozooids that bud gonophores Gonozooids – modified gastrozooids that bud gonophores
(permanently attached medusae that produce gonads)(permanently attached medusae that produce gonads) Dactylozooids – have nematocysts for protection. May capture Dactylozooids – have nematocysts for protection. May capture
food and transfer to gastrozooids food and transfer to gastrozooids
Typical Life CycleTypical Life Cycle
Diversity of Class HydrozoaDiversity of Class Hydrozoa
Order AnthoathecataeOrder Anthoathecatae Athecate (A-form)Athecate (A-form)
Examples:Examples: HydraHydra – gonochoric, also reproduce asexually, but lack medusa – gonochoric, also reproduce asexually, but lack medusa
phasephase
MilleporaMillepora – fire corals. Colonize axial rods of dead gorgonians. – fire corals. Colonize axial rods of dead gorgonians. Reef builders that have a nasty sting that burns like fireReef builders that have a nasty sting that burns like fire
VelellaVelella – by-the-wind sailor has a float with a sail, displays – by-the-wind sailor has a float with a sail, displays extreme polymorphism, with zooids that are suspended mouth-extreme polymorphism, with zooids that are suspended mouth-downdown
Male and female Male and female HydraHydra. Life. Lifecycle lacks cycle lacks medusa phasemedusa phase
MilleporaMillepora VelellaVelella
Order SiphonophoraOrder Siphonophora Polymorphic A-form Polymorphic A-form
hydrozoanshydrozoans
Pedal end of polyp is a gas-Pedal end of polyp is a gas-filled float known as a filled float known as a pneumatophorepneumatophore
Buds arise from column of Buds arise from column of polyp in sets called cormidia. polyp in sets called cormidia. Oldest is near float, and consist Oldest is near float, and consist of:of: GastrozooidGastrozooid GonozooidGonozooid Dactylozooid – long tentacle with Dactylozooid – long tentacle with
nematocystsnematocysts Bract – fleshy overhang that Bract – fleshy overhang that
protects zooidsprotects zooids
Prime example is Prime example is PhysaliaPhysalia, the , the Portuguese man of warPortuguese man of war
Order LeptothecataeOrder Leptothecatae
L-form hydroidsL-form hydroids
Feather-shaped Feather-shaped coloniescolonies
ObeliaObelia is the most is the most famous representativefamous representative
Order LimnomedusaeOrder Limnomedusae L – formL – form Polyp and medusa phasePolyp and medusa phase GonionemusGonionemus is prime is prime
exampleexample
One additional order, One additional order, TrachylinaTrachylina Life cycles are devoid of Life cycles are devoid of
the polyp phase in all the polyp phase in all members of this ordermembers of this order
Therefore, neither A-form Therefore, neither A-form or L-formor L-form