Chapter 9Cnidaria & Ctenophores

• Radial Symmetry- no head or tail end

• Equally responsive on all sides

• Mostly marine

• Cnidocytes-specialized cells for attachment, defense, & feeding

• Nematocyst- type of cnidocyte for food gathering & defense. May discharge a stinging tube or sticky secretions.

• Most are not harmful to humans

Portugese Man O War

Blue Box Jellyfish

Two forms of Cnidaria

• Polyp- sessile (attached and stationary). Mouth surrounded by tentacles. Ex: coral, sea anemone

• Medusae- free swimming. Inverted bowl shape w/ mouth on concave side. Ex: jellyfish

Body Layers

• Epidermis:

Gland Cells- near mouth, secrete mucous

Cnidocytes- contain nematocysts

Sensory Cells- have flagellum

Body Layers con’t• Mesoglea- jelly like

middle layer. In medusae, it’s thicker w/ elastic fibers

• GastrovascularCavity- functions in digestion, gas exchange, & discharge of gametes

Body layers con’t

• Gastrodermis- contain ciliated cells. Water is brought in by the beating cilia. Other cilia circulate the food.

• Gland cells- secrete digestive enzymes

Nervous System

• Nerve Net- diffuse nervous system. 2 networks of cells.

Signals can travel along synapses in both direction.

No myelin sheath on axon.

Symbiosis

Movement

• Polyps- permanently attached. Sessile

• Medusae- swim by contracting bell, expelling water from concave side. Elastic fibers in mesogleacompress for muscle contraction.

Feeding & Digestion

• Prey is drawn into gastrovascular cavity. Gland cells discharge enzymes onto food.

• Eat very small crustacea or small fish

Reproduction• Shed gametes into

water. Zygotes retained by female.

Embryo develops into free swimming larvae.

• Also repro. Asexually by budding.

Hydra

Obelia

Physalia Aurelia

Cubozoa

Anthozoa

Sea Anemone

polyps

Pipe Organ Coral

Ctenophores• Named for their 8 rows

of comb-like plates they use for movement.

• All marine

• Radial Symmetry

• Nerve Net

• Instead of nematocysts, tentacles have colloblasts (glue cells) to catch small prey.

• Free swimming. Beating cilia in comb plates move animal forwards or backwards.

• 100 species

• Called “sea walnuts”or “comb jellies”

The End