Invert Subgroup Guide-1

Overview of Kingdom Animalia

• All animals are eukaryotic, heterotrophic, multicellular organisms.

• Some have specialized body plans (segmentation, appendages, organ systems).

• Invertebrates share all the above characteristics but lack a vertebral column (backbone).

• There are eight major subgroups within invertebrates to study.

Invertebrate Animal Subgroups

• Porifera (sponges)

• Cnidaria (jellyfish, sea anemones, coral)

• Platyhelminthes (flatworms)

• Annelida (segmented worms)

• Nematoda (round worms)

• Arthropoda (insects, arachnids, crustaceans)

• Mollusca (squid, octopus, clams, snails)

• Echinodermata (starfish, sea urchins, sea cucumbers)

Porifera (Sponges)

• Characteristics:

  • Cellular level of organization; no true tissues.

  • Asymmetrical body plan.

  • Lacks segmentation.

  • Possess spicules for structural support.

Cnidaria (Jellyfish, Sea Anemones, Coral)

• Characteristics:

  • Diploblastic organization; made of endoderm and ectoderm.

  • Radial symmetry in body plan.

  • Lacks segmentation.

  • Exhibits polyp (sessile) and medusa (free-swimming) stages in life cycle.

  • Polyp stage often displays radial symmetry, while later growth forms may show asymmetry.

Platyhelminthes (Flatworms)

• Characteristics:

  • Triploblastic organization (endoderm, mesoderm, ectoderm); no body cavity (acoelomate).

  • Bilateral symmetry.

  • Dorsally flattened body shape.

  • Includes various forms such as flukes, tapeworms, and planaria.

Annelida (Segmented Worms)

• Characteristics:

  • Triploblastic coelomates (endoderm, mesoderm, ectoderm).

  • Bilateral symmetry.

  • Possess true segmentation.

  • Possess setae for movement (locomotion).

  • Composed of circular and longitudinal muscles.

  • Includes leeches, earthworms, sea mice.

Nematoda (Round Worms)

• Characteristics:

  • Triploblastic pseudocoelomates (endoderm, mesoderm, ectoderm).

  • Bilateral symmetry.

  • Lacks segmentation.

  • Possesses only longitudinal muscles.

  • Many are parasitic and cause health issues.

  • Molt a cuticle as they grow.

Arthropoda (Insects, Arachnids, Crustaceans)

• Characteristics:

  • Triploblastic coelomates (endoderm, mesoderm, ectoderm).

  • Bilateral symmetry.

  • Possess true segmentation.

  • Characterized by an exoskeleton, which is molted, and specialized jointed appendages.

  • Includes diverse groups: insects, arachnids.

Mollusca (Cephalopods, Bivalves, Gastropods)

• Characteristics:

  • Triploblastic coelomates (endoderm, mesoderm, ectoderm).

  • Bilateral symmetry.

  • Lacks segmentation.

  • Possess a shell-secreting mantle.

  • Includes squid, octopus, snails, clams, oysters, chitons.

Echinodermata (Starfish, Sea Urchins, etc.)

• Characteristics:

  • Triploblastic coelomates (endoderm, mesoderm, ectoderm).

  • Pentamerous radial symmetry (five distinct planes of symmetry).

  • Lacks segmentation.

  • Characterized by spiny skin and a deuterostome development.

  • Includes seastars, sea urchins, sand dollars, sea cucumbers, brittle stars.