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