Study Guide Chapter 33

1. Definition of Invertebrate

  • Invertebrates are animals that lack a vertebral column, or backbone.

2. General Characteristics of Invertebrate Phyla

  • Unique Characteristics: Invertebrates exhibit a wide variety of body plans and lifestyles.

  • Key Features:

    • Symmetry: Most invertebrates demonstrate either bilateral or radial symmetry.

    • Germ Layers: Invertebrates exhibit different numbers of germ layers (e.g., diploblastic, triploblastic).

    • Developmental Fate: Invertebrates are classified into protostomes (mouth develops first) or deuterostomes (anus develops first).

    • Reproductive Methods: Can reproduce sexually or asexually; some are hermaphroditic.

  • Examples of Invertebrate Phyla:

    • Porifera (sponges)

    • Cnidaria (jellyfish, corals)

    • Platyhelminthes (flatworms)

    • Annelida (segmented worms)

    • Mollusca (snails, clams, octopuses)

    • Arthropoda (insects, arachnids, crustaceans)

    • Nematoda (roundworms)

    • Echinodermata (starfish, sea urchins)

3. Important Characteristics of Porifera

  • General Traits:

    • Basal animals, representing some of the simplest life forms.

    • Lack true tissues and organs.

    • Hermaphroditic, able to produce both egg and sperm.

    • Often found as colonies with asymmetrical body plans.

    • Filter feeders, extracting nutrients from water.

  • Key Structures:

    • Spongocoel: The central body cavity where water is filtered.

    • Osculum: Opening at the top of the sponge where filtered water exits.

    • Ostia: Small pores through which water enters the sponge.

    • Mesohyl: Gelatinous matrix within the sponge that contains various cell types.

    • Choanocytes: Flagellated cells that create water currents and trap food particles.

    • Amoebocytes: Specialized cells that distribute nutrients and can differentiate into other cell types.

    • Spicules: Skeleton-like structures that provide form and protection; made of silica or calcium carbonate.

4. Important Characteristics of Cnidarians

  • General Traits:

    • Possess true tissues organized into distinct layers (ecto-, meso-, endoderm).

    • Exist in two primary forms: polyps (sessile) and medusas (free-swimming).

    • Predators, employing specialized cells for capturing prey.

  • Key Structures:

    • Polyp: Cylindrical body form attached to a substrate.

    • Medusa: Umbrella-shaped free-swimming body form.

    • Tentacles: Arm-like structures equipped with stinging cells.

    • Cnidocytes: Specialized cells containing nematocysts for capturing prey and defense.

    • Nematocysts: Stinging organelles within cnidocytes, used to immobilize or kill prey.

5. Lophotrochozoans

  • General Characteristics:

    • Organisms within this clade generally possess unique larval stages and a lophophore (tentacle-like feeding structure) or trochophore larva.

  • Phyla in Lophotrochozoans:

    • Platyhelminthes (flatworms)

    • Rotifera (rotifers)

    • Mollusca (mollusks)

    • Annelida (segmented worms)

5.1 Important Characteristics of Platyhelminthes (Flatworms)

  • Unique Trait: Exhibit remarkable regenerative abilities.

  • Classes of Platyhelminthes:

    • Turbellaria: Free-living flatworms like planarians.

    • Trematoda: Parasitic flukes.

    • Cestoda: Parasitic tapeworms.

5.2 Important Characteristics of Rotifers

  • General Traits:

    • Small, often microscopic animals found in aquatic environments.

    • Known for their complex reproductive strategies, which can include both parthenogenesis and sexual reproduction.

5.3 Important Characteristics of Mollusks

  • General Traits:

    • Soft-bodied animals often covered by a hard shell.

    • Exhibit a larval stage known as trocophore.

  • Body Plan Structures:

    • Muscular Foot: Used for locomotion and attachment.

    • Visceral Mass: Contains internal organs.

    • Mantle: Tissue layer that secretes the shell and covers the visceral mass.

    • Radula: Tongue-like structure used for feeding.

  • Important Mollusk Groups:

    • Chitons: Marine mollusks with eight armored plates.

    • Gastropods: Include snails (terrestrial and aquatic); exhibit torsion during development.

    • Bivalves: Examples include oysters, mussels, and clams. Filter-feeders characterized by two shells; significant historical extinction rates.

    • Cephalopods: Active marine predators such as octopuses and squids. Highly developed nervous systems characterized by complex brains and ganglia within arms.

5.4 Important Characteristics of Annelids (Segmented Worms)

  • General Traits:

    • Divided into two clades: Errantia (free-moving) and Sedentaria (sedentary).

    • Possess a complete digestive system.

  • Errantia: Have parapodia (appendages) for movement; often mobile.

  • Sedentaria: Less mobile and includes important ecological species such as earthworms, which improve soil quality and fertility; reproduce sexually and asexually.

6. Ecdysozoan Clade

  • General Characteristics:

    • Organisms that share an ability to molt a chitinous exoskeleton as they grow.

  • Phyla in Ecdysozoans:

    • Arthropoda (arthropods)

    • Nematoda (nematodes)

6.1 Important Characteristics of Arthropods

  • Success Factors:

    • Segmented body plan allows for specialization of body segments, contributing to adaptability and success in diverse environments.

    • Adaptations in gas exchange organs (e.g., gills, tracheae) help circumvent hard exoskeletons.

    • Arthropods grow by molting (ecdysis), shedding their exoskeleton to allow for size increases.

6.1.1 Chelicerates

  • Key Features:

    • Possess feeding appendages called chelicerae and lack antennae.

  • Examples: Include spiders, horseshoe crabs, mites, and scorpions.

  • Human Benefits: Many chelicerates like spiders can control insect populations, contributing to ecological balance.

6.1.2 Myriapods

  • Examples: Include millipedes (herbivorous) and centipedes (carnivorous).

6.1.3 Crustaceans

  • Examples: Includes crabs, lobsters, shrimps, barnacles, and copepods, many of which serve critical roles in aquatic ecosystems.

6.1.4 Insects

  • Key Features:

    • Possess six legs and exhibit a wide variety of ecological roles.

    • Evolution of wings played a significant role in the diversification and success of insect species.

    • Metamorphosis Types:

      • Complete Metamorphosis: Includes stages of larva, pupa, and adult.

      • Incomplete Metamorphosis: Involves nymph stages leading to adults without a distinct larval form.

6.2 Important Characteristics of Nematodes (Roundworms)

  • Key Traits:

    • Exist as both free-living and parasitic organisms.

    • Possess a muscular body wall that facilitates thrashing motions.

7. Deuterostomes

  • Phyla in Deuterostomes:

    • Include Echinodermata (starfish, sea urchins) and Chordata (vertebrates, tunicates).

7.1 Important Characteristics of Echinoderms

  • Key Traits:

    • Possess an endoskeleton made of calcified plates.

    • Radial symmetry in adult forms but exhibit bilateral symmetry in larvae.

    • Have a water vascular system crucial for movement and feeding.

  • Function of Water Vascular System: Facilitates locomotion, feeding, and gas exchange through a network of canals and tube feet.

  • Classes of Echinoderms:

    • Asteroidea: Includes starfish, equipped with a central disc and several arms; capable of external digestion and regeneration; notably affected by sea star wasting disease.

    • Echinoidea: Includes sea urchins and sand dollars; typically herbivorous, characterized by spines and Aristotle's lantern (a complex feeding structure).

    • Holothuroidea: Includes sea cucumbers; lack a rigid endoskeleton, soft-bodied with leathery skin.

1. Definition of Invertebrate

  • Invertebrates are animals that lack a vertebral column, or backbone.

2. General Characteristics of Invertebrate Phyla

  • Key Features:

    • Symmetry: Bilateral or radial.

    • Germ Layers: Diploblastic or triploblastic.

    • Developmental Fate: Protostomes (mouth first) or deuterostomes (anus first).

    • Reproductive Methods: Sexual, asexual, or hermaphroditic.

  • Examples of Invertebrate Phyla:

    • Porifera (sponges)

    • Cnidaria (jellyfish, corals)

    • Platyhelminthes (flatworms)

    • Annelida (segmented worms)

    • Mollusca (snails, clams, octopuses)

    • Arthropoda (insects, arachnids, crustaceans)

    • Nematoda (roundworms)

    • Echinodermata (starfish, sea urchins)

3. Important Characteristics of Porifera

  • General Traits:

    • Basal animals, simplest forms.

    • Lack true tissues and organs.

    • Hermaphroditic; asymmetrical.

    • Filter feeders.

  • Key Structures:

    • Spongocoel: Central cavity.

    • Osculum: Water exit.

    • Ostia: Water entry pores.

    • Mesohyl: Gelatinous matrix.

    • Choanocytes: Flagellated cells for current and food trap.

    • Amoebocytes: Distribute nutrients, differentiate.

    • Spicules: Skeleton of silica or calcium carbonate.

4. Important Characteristics of Cnidarians

  • General Traits:

    • Possess true tissues.

    • Two forms: polyps (sessile) and medusas (free-swimming).

    • Predators.

  • Key Structures:

    • Polyp: Cylindrical, attached form.

    • Medusa: Umbrella-shaped, free-swimming form.

    • Tentacles: Arm-like with stinging cells.

    • Cnidocytes: Specialized cells with nematocysts.

    • Nematocysts: Stinging organelles.

5. Lophotrochozoans

  • General Characteristics:

    • Unique larval stages and/or a lophophore (feeding structure) or trochophore larva.

  • Phyla in Lophotrochozoans:

    • Platyhelminthes (flatworms)

    • Rotifera (rotifers)

    • Mollusca (mollusks)

    • Annelida (segmented worms)

5.1 Important Characteristics of Platyhelminthes (Flatworms)

  • Unique Trait: Regenerative abilities.

  • Classes:

    • Turbellaria: Free-living (e.g., planarians).

    • Trematoda: Parasitic flukes.

    • Cestoda: Parasitic tapeworms.

5.2 Important Characteristics of Rotifers

  • General Traits:

    • Small, microscopic aquatic animals.

    • Complex reproductive strategies (parthenogenesis, sexual reproduction).

5.3 Important Characteristics of Mollusks

  • General Traits:

    • Soft-bodied, often with a hard shell.

    • Trocophore larval stage.

  • Body Plan Structures:

    • Muscular Foot: Locomotion/attachment.

    • Visceral Mass: Internal organs.

    • Mantle: Secretes shell, covers visceral mass.

    • Radula: Tongue-like feeding structure.

  • Important Mollusk Groups:

    • Chitons: Marine, eight armored plates.

    • Gastropods: Snails; exhibit torsion.

    • Bivalves: Oysters, mussels, clams; filter-feeders, two shells.

    • Cephalopods: Octopuses, squids; active marine predators, highly developed nervous systems.

5.4 Important Characteristics of Annelids (Segmented Worms)

  • General Traits:

    • Complete digestive system.

    • Clades:

    • Errantia: Free-moving, have parapodia.

    • Sedentaria: Less mobile (e.g., earthworms), improve soil quality.

6. Ecdysozoan Clade

  • General Characteristics:

    • Molt a chitinous exoskeleton as they grow.

  • Phyla in Ecdysozoans:

    • Arthropoda (arthropods)

    • Nematoda (nematodes)

6.1 Important Characteristics of Arthropods

  • Success Factors:

    • Segmented body: Specialization improves adaptability.

    • Adaptations in gas exchange (gills, tracheae).

    • Grow by molting (ecdysis) exoskeleton.

6.1.1 Chelicerates

  • Key Features: Feeding appendages called chelicerae, lack antennae.

  • Examples: Spiders, horseshoe crabs, mites, scorpions (control insect populations).

6.1.2 Myriapods

  • Examples: Millipedes (herbivorous), centipedes (carnivorous).

6.1.3 Crustaceans

  • Examples: Crabs, lobsters, shrimps, barnacles, copepods (critical aquatic roles).

6.1.4 Insects

  • Key Features: Six legs, diverse ecological roles.

  • Wings: Significant for diversification and success.

  • Metamorphosis Types:

    • Complete: Larva, pupa, adult.

    • Incomplete: Nymph stages leading to adults.

6.2 Important Characteristics of Nematodes (Roundworms)

  • Key Traits:

    • Free-living and parasitic forms.

    • Muscular body wall for thrashing motions.

7. Deuterostomes

  • Phyla in Deuterostomes:

    • Echinodermata (starfish, sea urchins)

    • Chordata (vertebrates, tunicates)

7.1 Important Characteristics of Echinoderms

  • Key Traits:

    • Endoskeleton of calcified plates.

    • Radial symmetry in adults, bilateral in larvae.

    • Water vascular system for movement, feeding, gas exchange.

  • Classes of Echinoderms:

    • Asteroidea: Starfish; central disc, arms; external digestion, regeneration.

    • Echinoidea: Sea urchins, sand dollars; herbivorous, spines, Aristotle's lantern.

    • Holothuroidea: Sea cucumbers; lack rigid endoskeleton, soft-bodied.