Earliest form w/ body cavity

Mouth surrounded by tentacles

Body wall – 3 layers (not tissues): epidermis (tissue), mesoglea (not tissue), gastrodermis (tissue)

Cnidaria – diploblastic ( 2 germ layers)

Ectoderm

Endoderm

Mesoglea - middle layer– forms from basement membrane

Thin noncellular layer

Or thick jelly w/ mobile cells

Characteristics-general

Mostly marine (a few freshwater forms)

2 body styles

from Barnes - Invertebrate Zoology - 5th Ed.

polypoid

cylindrical,

aboral end facing down (as basal disc),

oral end facing up

thin mesoglea

medusoid

umbrella shaped,

aboral up convex and facing upward,

oral end concave and facing down,

thick mesoglea

Tissues

Epidermis – 5 cell types

Epitheliomuscular – usually columnar, base next to mesoglea, several basal contractile extensions

Interstitial cells

Round shape

Beneath surface & between epitheliomuscular cells

Forms sperm & eggs & other cells

Cnidocytes – unique to phylum

from Barnes - 5th Ed. Invertebrate Zoology

Cells with eversible organelles-cnidae

Variable and species specific (taxonomically useful)

Located between eptheliomuscular cells

Cell base anchored to epitheliomuscular basal extensions

Coiled & pleated tube in intracellular capsule

Nematocyst – stinging cnida – open thread, w/ barbs, penetrates & may poison- present in all classes

Desmonemes – tangling, closed threads lined w/ spines – not poisonous

Cnidocil – bristle trigger (not in Anthozoans)

Hinged operculum or lid on cnidocyte

Firing of cnidae -Some nerve control (synchronization?)

Mechanical or chemical stimuli

Cell permeability changes

Operculum flips open

Firing sequence – 2-phased

Lid opens and stylets penetrate prey

Thread uncoils inside of prey

Prey capture

Proteinaceous poison paralyzes

Closed thread w/ spines adheres

Cnidocyte replacement (within 48 hours from interstitial cells)

Mucus- secreting cells

Receptor (sensory) cells – columnar with sensory spheres or bristles

Nerve cells – cf. animal multipolar nerve cells

Gastrodermis – with symbiotic zooxanthellae

Nutritive-muscle cells (cf. epitheliomuscular) – flagellated, form circular muscle bands

Enzymatic gland cells- wedge-shaped & flagellated

Mucus-secreting cells

Nerve cells – few in number

Movement

Gastrovascular cavity – hydrostatic skeleton

Gastrodermis sweeps water in with flagellae

Longitudinal epidermal contractile threads bend body

Feeding

Carnivorous on small crustaceans

Nematocysts – entangle & poison

Tentacles – transfer to mouth

Gas Exchange & Excretion

Across body surface

Oxygen & Nitrogenous wastes

Water diffuses in through surface

GVC receives water (hypotonic) from tissue and pumps it out

Nervous system

Somewhat complex

2 neural networks

epidermal (only network in hydra)

gastrodermal

nerve types

sensory – motor – interneural

activity

bidirectional transmission (differs from higher animals)

Reproduction

Hydras – usually asexual – budding

Body wall along with its GVC evaginates

Tentacles form on the bud and it detaches

Regenerative ability

Trembley (1744) – pulls knotted thread thru basal disc – turns animal inside out – cells migrate and re-establish epidermis & gastrodermis

Either gastrodermis or epidermis forms a whole new animal

Polarity - Slice up a hydra and each slice forms tentacles at oral (and basal disc at other end)

Hydras continually replace all cells – never grow old

Sexual reproduction

During fall w/ overwintering eggs

Dioecious

Germs cells form from interstitial cells

True for most Cnidaria

Interstitial cells aggregate into ovaries and testes

Testes on upper body half

Ovaries on lower body half

One egg per ovary

Epidermis ruptures to expose egg

Fertilized by sperm released to water from testis

Egg covered w/ chitinous shell

Drops off and lays dormant thru winter

Shell softens in spring & young hydra emerges

Class Hydrozoa

General characters

Small, “plant-like”, overlooked or considered as “seaweed” on wharves

Has the few freshwater forms

Has either polypoid or medusoid (or both) stages in life cycle

Unique characters

Non-cellular mesoglea

Gastrodermis w/o cnidocytes

Gametes released from epidermis (at least never to GVC)

Structure

Most w/ polypoid stage

Some solitary

Most colonial

Budding w/ buds remaining attached (contrast with hydra)

Repeated budding forms colony

Tissue layers (& mesoglea) continuous thru colony

Stalk – called a hydrocaulus

Polyp – in general called a hydranth

Stolon – rootlik – hydrorhiza

Covered w/ chitinous support – perisarc

Chitin around stalk – called a coenosarc

Chitin around polyp – called a hydrotheca

Forms w/ hydrotheca – thecate

Forms w/o hyrdotheca - athecate

Colony form

Arborescent (treelike)

or Pinnate (or featherlike)

Or single polyps from stolon

from Barnes - Invertebrate Zoology - 5th Ed.

Small size & lacking color

Polymorphism in terms of different types of polyps

Gastrozooid (trophozooid)

A polyp which feeds on zooplankters

Extracellular digestion occurs w/in gastrozooid

Then passed to common GVC

Intracellular digestion occurs thereafter

Dactylozooids

Are defensive polyps (gastrozooids may do this instead)

w/ cnidocytes and adhesive cells

Located around gastrozooids

Gonozooids areproductive polyps (gonangium in Obelia)

Produce medusoid form (seen as medusa buds)

Medusae produce gametes

Floating hydroid colony

Porpita,Velella and Physalia

Medusoid forms

Have an umbrella shape (exumbrella = top, subumbrella = bottom)

With a shelf at margin – velum (only in hydrozoan medusae)

their Mesoglea – thick jelly w/ fibers but no cells

They are capable of movement

Contractile sheets form from epidermal cells

These sheets are radial and circular

Contraction of these sheets results in pushes water out  of bottom of medusa (velum helps)

Fibers in mesoglea return form to proper shape

Mostly vertical movements (rising & sinking)

Currents provide lateral movement

Reproduction/ life cycle

Most are dioecious

Medusae reproduce sexually

Gonads are located on radial canals in subumbrellar epidermis

Fertilization is external, ( or on the manubrium, or internal

Embryo develops in gonad

Planula larvae released (radial but with an anterior end)

Class Scyphozoa

General characters

Jellyfish- medusae are dominant (polypoid forms appear only as larva)

Strikingly colored (deep orange, pink)

Cosmopolitan in oceans

Coastal nuisance

Cubomedusae – Australian, death when it occurs is within 3 – 20 minutes

Mostly free-living, some sessile forms (Stauromedusae)

Unique characters

Medusae without the shelf – velum (except Cubomedusae)

Mouthstalk – manubrium- drawn out as frilly oral arms and w/ stinging cells

Mesoglea – thick and contains amoeboid cells (that come from epidermis)

Movement

Band of fibers from contractile cells in mesoglea

Form circular contractile band

Pulse and move animal vertically

Feeding

Carnivorous – plankton to small fish

Predators or filterers (Aurelia)

Mouth to  manubrium to central stomach to four radial gastric poulches

Gastric pouches formed by septa but are interconnected

Edge of septa with cnidocytes & nematocysts

Extracellular digestive enzymes

Nerve control

Neural concentrations at points along umbrellar margin – termed rhopalium

Sensory neurons also in rhoplaium

Ocelli usually simple eyes (developed with lenses in Cubomedusae) also in rhopalium

Reproduction

Mostly dioecious

Gonads on gastrodermis (on epidermis in hydozoans)

Eggs and sperm released to GVC then out mouth

Planula larvae swim and settle and form polyp (scyphistoma)

Scyphistoma divides transversely (strobilation)  to form one or many immature medusae – asexual reproduction

Nearly microscopic medusae termed ephyrae

Medusae are released and mature into sexual medusae

Class Anthozoa

General characters

Solitary or colonial polyps (no medusoid stage)

Largest Cnidarian class

Unique characters

Tubular pharynx connects mouth to GVC

GVC septate & in radial compartments

Cnidocytes & gonads on septa

Sea anemones

Solitary

Large and heavy

Often bright colors

Diverse in tropics

Stony (scleractinian) corals

Largest order

Mostly colonial

Polyphs w/o siphonoglyphs

Calcium carbonate – external skeleton

Secreted by epidermis on lower column of polyp

Lateral outpouches of GVC connect polyps together

Thus living tissue overlies skeleton

Also secretes calcium carbonate on bottom surface.

Periodically “lifts” skirt of tissue and lays new calcium carbonate layers (pock marks longitudinally)

Secretes calcium carbonate at different rates based on light and temp. (“growth rings”)

Feedings

Carnivorous on small organisms (plankton)

Many nocturnal

Many w/ symbiotic algae (zooxanthellae in gastrodermis)

Reproduction

Sexual and asexual

Planula larvae produced, settle, polyp produced from it

Octocorals – sea pansies, sea pens, sea whips, & sea fans

8 tentacles (always pinnate)

small colonial polyps

mesogleal amebocytes make internal skeleton of calcium carbonate

internal calcium carbonate gives color to animal (also due to zooxanthellae)