Chapter 8: Lower Invertebrates

Introduction

• Shift from photosynthesizers to marine animals
• Animals: multicellular, true cells, no cell walls, can't make own food
• Marine animals: invertebrates (no backbone) and vertebrates (have backbone)
• Majority are invertebrates

Sponges (Phylum Porifera)

Characteristics

• Likely one of the first animals
• Asymmetrical, Cecil (immobile)
• Specialized cells but no tissue areas

Types of Cells

• Collar cell: Flagella circulates water, moves food/oxygen in, waste out
• Pinacocytes: Skin cells
• Archaeocytes: Amoeboid cells repairing tissues

Anatomy and Forms

• Water flows in, through collar cells, out through osculum
• Body forms: asconoid, syconoid, leuconoid (complex)

Reproduction

• Asexual: Budding, fragmentation
• Sexual: Hermaphroditic, produce eggs (archaeocytes) and sperm (collar cells)
• Larvae: Planktonic amphiblastula

Ecological Roles

• Compete with corals, bryozoans
• Produce chemicals to combat competitors
• Spicules deter predators
• Symbiosis with organisms like shrimp

Cnidarians

Types

• Jellyfish, hydroids, corals, sea anemones
• Stinging cells: Nematocysts with nematocytes

Anatomy and Symmetry

• Body structure: Skin, gastrodermis, mesoglia
• Radial symmetry: equal halves in any direction
• Forms: Polyp (tentacles around mouth), Medusa (umbrella-shaped jellyfish)

Reproduction

• Asexual: Budding, fission
• Sexual: Sperm and egg released in water column
• Larvae: Planular larva

Relationships

• Symbiotic relationships (mutualistic, commensalism)
• Coral reefs: Provide habitat for various marine life

Dangerous Species

• Box jellyfish (Cuba zoans): Highly venomous
• Irukandji jellyfish: Deadly sting
• Examples: Nudibranchs ingesting Portuguese man-of-war

Comb Jellies

Characteristics

• Lack stinging cells
• Planktonic, transparent, bioluminescent
• Status bubble helps orientation

Feeding

• Plankton, larva fish, fish eggs
• Use colloblasts (sticky cells) to capture prey

Reproduction

• Mostly hermaphroditic
• Larvae develop into adults

Bilateral Symmetry

Overview

• Single directional symmetry, distinct head region

Flatworms

Types

• Tubularians, flukes, tapeworms

Characteristics

• Benthic dwellers, sensory receptors
• Asexual (hermaphroditic), penis fencing during mating

Ecological Role

• Nutrient cycling
• Parasitic nature (e.g., sperm whale tapeworm)

Ribbon Worms

• Benthic, external fertilization
• Proboscis used to catch prey

Lophophorates

Overview

• Tube-dwelling, filter feeders

Types

• Phoronoids: Tube secretors, planktonic stage
• Bryozoans: Colonial, planktonic, abundant
• Brachiopods: Two different shaped shells, benthic

Conclusion

• Importance of lower invertebrates in marine ecosystems
• Impact on nutrient cycling, relationships, and marine life habitats