phylum cnidaria - mr. davidson - behs science a/documents/phylum cnidaria.pdf · general...

Phylum CnidariaTHE JELLYFISH, ANEMONES AND CORALS

General characteristics of phylum Cnidaria:

General characteristics of phylum

Cnidaria:

� Radial Symmetry

� Specialized Tissues

Sensory system- nerve net � Sensory system- nerve net

� Specialized cells stinging cells -cnidocytes

�Carnivores

�All aquatic, mostly marine

�Asexual and sexual reproduction

Fun Facts

� About 9000 species of cnidarians

� Oldest jellyfish, 500 million years old- found in Utah

Cnidocytes

Cnidocytes

� Stinging cells found in the tentacles

� Each cell has a tightly coiled, poison filed, dart-like structure-poison filed, dart-like structure-nematocyst

� Nematocyst has a trigger hair-cnidocil

� Contact with the cnidocil causes the nematocyst to discharge

� Fills with water

� Often has barbs

Tissue Structure

� Cells arranged

into tissues- two

layers

Outer layer: � Outer layer:

epidermis

� Inner layer:

gastrodermis

� In between layer

is jelly-like:

mesoglea

Body Plan

� Radial symmetry with central mouth

� Tentacles surround mouth and extend

from bodyfrom body

Life Cycle

� Most cnidarians have 2 body forms in

their life history

Life Cycle

�Polyp- asexual

and sessileand sessile

�Medusa-

dioecious and

free swimming

� VIDEO

� Birth of the Sea Nettle

� http://www.youtube.com/watch?v=NOf2RRmSkgQ� http://www.youtube.com/watch?v=NOf2RRmSkgQ

&edufilter=Ps5lSoPViR6fXm1RM5Eu1Q

� Arkive – Polyp Birth, Baby Swim

� Overview

� http://www.youtube.com/watch?v=O9Bl6TQmBE0&edufilt

er=Ps5lSoPViR6fXm1RM5Eu1Q

� /

Animal Functions

� Feeding

� Circulation

� Respiration� Respiration

� Excretion

� Response

� Movement

� Reproduction

� Video – Shape of Life

Feeding

� After stinging, prey is pulled into the

gastrovascular cavity

� Digestive chamber, 1 opening

� Extracellular digestion begins and � Extracellular digestion begins and

nutrients are absorbed

Feeding

� Cnidarians eat small crustaceans and fish

� Waste passes back out the mouth

VIDEO – ARKIVE� VIDEO – ARKIVE

Respiration, Circulation and

Excretion

� What do you think?

Respiration, Circulation and

Excretion

� Gastrovascular cavity brings oxygen in and waste

passes out

� Circulation is by diffusion from one cell to the next � Circulation is by diffusion from one cell to the next

Response - Senses

� Nerve net: Nerve cells that connect

around the bodyaround the body

� Cnidarians can feel touch

� Some have cells that sense gravity or light

� Coordinates movement and response

Movement

� Hydrostatic skeleton – muscles push

against water filled cavities

� Polyps can somersault or inch along

� Medusa swim or float

� VIDEO

� Anemone

� http://www.youtube.com/watch?v=Dm98n3908QM

� Dance of the Jellyfish

� http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/dance-jellyfish-eorg

Reproduction

�Asexual

�Medusa bud from a polyp

�Polyps can bud other polyps

�Sexual

�External fertilization

�Males and females

�Eggs and sperm are released

into the water

Cnidarian Diversity

�Classes

�Hydrozoa�Hydrozoa

�Scyphozoa

�Cubozoa

�Anthozoa