06 Chap 13 Cnidaria and Ctenophora

Phylum Ctenophora

Comb Jellies

sk. Parazoa

Protostomeembryology

Deuterostomeembryology

ph. Cnidariaph. Porifera

sk. Eumetazoa

asymmetrical, cellular level

Bilateral,triploblastic

Radial,diploblastic

symmetrical, tissue level

choanoflagellate-like ancestor

k. Animalia

Ctenophore biology

• 100-150 species• 8 rows of comblike plates for

locomotion• Lack stinging cells (except 1 sp.)

– Cnidocytes from prey• Colloblasts- glue cells used for

feeding and adhesion

Ctenophore Diversity

Beroa

Cestum

Coeloplana, rarecreeping

Ctenophore Taxa

• Class Tentaculata– Tentacle bearing

• Class Nuda– Tentacles absent

Phylum Cnidaria

Radially symmetrical Eumetazoathat sting

Major Characteristics

• Two tissue layers– epidermis and gastrodermis, connected

by non-cellular mesoglea• Radial symmetry• Cnidocytes - stinging cells• Incomplete gut - “gastrovascular cavity”• Polyp, medusa, and planula body forms

CnidocyteLike Hickman Fig. 13-3

cnidocil ortrigger

nucleus

20 types of nematocysts!

2m/s

40,000x accel. gravity

A fearsome tiny weapon !

A combination of osmoticand hydrostatic pressureopens the opeculum forces outthe thread

Two Types of BodiesFig. 13.2

polyp(attached, mouth-up)

medusa(free-drifting, mouth-down)

Cnidarian Cell Types– Cnidocytes

• Stinging cells (penetrants, volvents, glutinants)– epithelio-muscular

• covering and muscular contraction, epidermal, shorten body or tentacles

– nutritive-muscular• Circulate water and food

– Gland• Secrete adhesive and create gas bubble

– sensory / nerve• Coordinate movement

– interstitial• Stem cells found at base of epitheliomuscular cells

Hydra Cell Typesfood in gastro-vascular cavity

gland cell

cnidocytes

epithelio-muscular cell

nutritive-muscular cell

mesoglea

interstitial cell

Cnidarian Life Cycles• Sexual medusa

– has gonads, produces gametes by meiosis• Drifting planula

– non-feeding, short-lived, settles in new location

• Asexual polyp– reproduces by budding

Obelia Life Cyclecompare Fig 13.9

planula larva

medusa

polyp

asexual buddingforms a colony

sexual fertilization

Aurelia Life CycleHickman Fig. 13.18

syphistoma strobila

Classification of the Cnidaria

• phylum Cnidaria– class Hydrozoa– class Scyphozoa– class Anthozoa

Class Hydrozoa

• Polyp usually dominant• Medusa is usually small and short-lived

– freshwater Hydra has no medusa OR planula

– medusas of one order (including Man-’o-War) remain attached to colony

• Some polyp colonies resemble hard corals– fire corals

Hydrozoan Polyp Colony

More Hydrozoans

A hydrozoan medusa

freshwater Hydra with ovary

float (modified polyp)gamete-producing medusoidsfeeding hydroidsstinging tentacles

HydrozoanMan-’o-War

Colonycompare Hickman

Fig. 13.14

Class Scyphozoa

• solitary medusa stage is dominant– some are nearly 10m long

• polyp small and short-lived– buds off juvenile medusas, not more

polyps• “true” jellyfish

ScyphozoaFig 13.19

Class Cubozoa• Formerly a subdivision of Scyphozoa

Class Anthozoa• medusa absent• Polyp dominant, often small but produces

large colonies in amazing forms– polyp produces gametes– sometimes compared to a sessile medusa– planula disperses

• hard and soft corals, sea anemones, sea fans, sea pansies, sea whips

AnthozoaFig. 13.21

Sea pen

Sea fan, whip coral

Sea anemone

The End.