Phylum Cnidaria

Jelly Fishes

Sea Anemones

Corals

Phylum Cnidaria

• A.k.a Coelenterata or Radiata

• Differ from sponges - have rudimentary organs

Morphology

• Body wall - 3 layers

• Epidermis

• Gastrodermis

• Mesoglea

Body plans

• Sessile - Polyp (hydranth or hydroid)

• Cylindrical stalk and oral end with tentacles

Body Plan

• Free swimming - Medusa

• Bell shaped

• Mesoglea constitutes bulk

Cell Types

• Epithelio-muscle cells• Cover and protect• Can contract (muscular properties)

• Interstitial cells• Production of gamets

• Mucous secreting cells (Gland cells)

• Nerve cells

• Cnidocytes

Cnidocyte

• On Tentacles• Defense and feeding

• Nematocyst

• Cnidocil - trigger

Nervous System

• First time

• Nerve net

• 2 nets • Associated with epidermis and gastrodermis

Classification

• 3 Classes

• Hydrozoa

• Scyphozoa

• Anthozoa

Hydrozoa

• Polymorphic• Polyp - Hydra• Medusa - Obelia

• Simple gastrovascular cavity - no septa

• No nematocysts in digestive cavity

• Solitary or colonial

Close-up of Hydroid

Hydroid medusa

Composition of Colonies

• 3 types of individuals

• Gastrozooid - responsible for feeding also numerous

• Gonozooid - sexual reproduction

• Dactylozooids - defense and food capture

Life Cycles

• 3 basic types• Obelia - both polyp and medusa

stage• Hydra - only polyp

– Asexual reproduction - budding

• Physalia - Colony attached to float called Pneumatophore

Scyphozoa

• Exclusively marine

• Medusa dominant stage

• Much larger in size compared to hydrozoan medusae

Scyphozoa• Mesoglea makes up large portion of body• Gastrovascular cavity divided by septa• complex system of canals in medusa to

help move food and oxygen• Muscular system on outer edge of

medusa• Very toxic - can kill in 30 secs or less

Sense organs

• 8 compound marginal sense organs– 2 sensory pits - chemoreception

– 1 ocellus (eye spot) - light sensing

– tactile structures - touch sensitive

– 1 statocyst - orientation and balance

Reproduction

Anthozoa• None have medusa

- Only Polyp• Hence Sessile• Several Septa in

Gastro-vascular cavity

• Attached to substrate by Pedal Disk

Phylum - Ctenophora

Combjellies or Sea Walnuts

• Offshoot of Medusa like Cnidarian

• Transparent animals

• Never colonial

• Free swimming

• No nematocysts instead have COLLOBLASTS – adhesive cells

Characteristics

• 8 rows of fused cilia (combs)

• Nervous system – nerve net

• Single sense organ – Statocyst

• Cydippid larva• Bioluminescence