Invertebrates

Objectives

• Overview of invertebrate classification
• Describe Porifera invertebrates
• Outline characteristics of cnidarians
• Overview of platyhelminths

Most invertebrates are insects.

Embryo Development

• Protostome
• Deuterostome

Protostomes

• Coelem forms within mesoderm
• E.g., mollusks, annelids, arthropods

Deuterostomes

• Coelem forms from a pouch of endoderm
• E. g., echinoderms and chordates

Porifera

Porifera

• Adult sponges are sessile.
• Endoskeleton of spicules

Filter-feeders

• Spongocoel: large central cavity
• Collar cells filter out food particles
• Collar cells and amebocytes digest food
• Water and waste flows out of osculum
• Oxygen from diffusion

Reproduction

• Asexual by budding
• Adults produce egg and sperm
• Sperm released through osculum
• Larva is motile, covered with cilia

Cnidarians

Cnidarians

• Radial symmetry
• Tissues
• Nematocyst - stinger (with poison)

Cnidarian Bodies

• Endoderm and ectoderm 
• Coelenteron - simple digestive cavity
• Sessile polyp or motile medusa
• Nerve net that can detect touch

Reproduction

• Polyps reproduce asexually
• Medusae reproduce sexually

Platyhelminthes

Flatworms

• 1 mm to 20 m long
• No coelem or pseudocoelem
• No respiratory system (diffuse instead)
• Incomplete digestive system
• Have a mesoderm

Reproduction

• Sexually
• Same individual produces egg and sperm
• After fertilization egg leaves and forms larva

Ecology

• Most free living in aquatic habitats
• Some are parasites (e.g., tapeworms)