Biological Diversity: Porifera, Cnidaria, Lophotrochozoa

Learning Objectives

• Illustrate phylogenetic relationships among major animal groups and key adaptations:
  • Tissues, bilateral symmetry, protostome vs. deuterostome development, ecdysis, and lophotrochozoan characteristics.
• Describe morphological, functional characteristics, adaptive value, and ecological roles of nine animal phyla:
  • Porifera, Cnidaria, Platyhelminthes, Mollusca, Annelida, Nematoda, Arthropoda, Echinodermata, Chordata.
• Identify invertebrate phylum based on morphological description or images.
• Explain characteristics of subgroups of invertebrates:
  • Cnidaria (hydrozoa, scyphozoa, anthozoa)
  • Platyhelminthes
  • Mollusca (gastropoda, bivalva, cephalopoda)
  • Arthropoda (hexapoda, crustacea, chelicerata)
  • Echinodermata (asteroidea, ophiuroidea, echinoidea, holothuroidea)
  • Chordata (cephalochordata, urochordata)
• Define key terms:
  • Choanocyte, Amoebocyte, Filter feeder, Polyp, Medusa, Gastrovascular cavity, Intracellular digestion, Extracellular digestion, Cnidocyte, Nematocyst, Exoskeleton, Endoskeleton, Alimentary canal, Complete digestive tract, Foot, Mantle, Visceral mass, Radula, Cuticle, Molting, Open circulatory system, Closed circulatory system, Water vascular system, Tube feet, Notochord.

Phylogenetic Relationships of Animal Kingdom

• Evolutionary Timeline:
  • Metazoa (770 million years ago) → Eumetazoa (680 million years ago) → Bilateria (670 million years ago)
• Major Animal Groups include:
  • Porifera (sponges)
  • Ctenophora (comb jellies)
  • Cnidaria (jellyfish, corals)
  • Acoela
  • Hemichordata
  • Echinodermata (sea stars, sea urchins)
  • Chordata (vertebrates)
  • Platyhelminthes (flatworms)
  • Rotifera (wheel animals)
  • Ectoprocta
  • Brachiopoda
  • Mollusca (snails, clams)
  • Annelida (segmented worms)
  • Nematoda (roundworms)
  • Arthropoda (insects, arachnids)
  • Lophotrochozoa, Ecdysozoa, Deuterostomia.

Phylum Porifera (Sponges)

• Characteristics:
  • Approximately 8,000 species, mainly marine.
  • Lack symmetry and true tissues; composed of specialized cells (e.g., choanocytes, amoebocytes).
  • Adult sponges are benthic, sessile filter feeders.
• Anatomy:
  • Water flows through pores into a central cavity (spongocoel) and exits through the osculum.
  • Reproduce both sexually (internal fertilization) and asexually (budding).

Phylum Cnidaria

• Characteristics:
  • Radial symmetry, mostly marine. Diploblastic with two germ layers (ectoderm, endoderm).
  • Possess tissue and gastrovascular cavity for extracellular digestion.
  • Nervous system organized into a nerve net without central control.
• Body Forms:
  • Exhibit two forms: polyps (sessile) and medusae (free-swimming).
• Major Classes:
  • Hydrozoa: Includes Obelia, Hydra, and Portuguese man-of-war.
  • Scyphozoa: Jellyfish; medusa stage is dominant and large.
  • Anthozoa: Sea anemones and corals, lacking medusa stage.
  • Cubozoa: Box jellies; primarily marine and have a potent venom.

Phylum Platyhelminthes (Flatworms)

• Characteristics:
  • Bilaterally symmetrical, predatory lifestyle, acoelomates (lack coelom).
  • Have a gastrovascular cavity with a blind gut.
• Reproduction:
  • Capable of sexual and asexual reproduction (many are hermaphroditic).
• Classes:
  • Turbellaria: Free-living flatworms, mostly marine.
  • Monogenea: Parasites of fish.
  • Trematoda: Flukes with complex life cycles.
  • Cestoda: Tapeworms that absorb nutrients from the host's intestine.

Phylum Mollusca

• Characteristics:
  • Diverse group with over 100,000 species characterized by soft bodies, often with hard shells.
  • Body divided into three parts: foot, visceral mass, and mantle (which may secrete the shell).
• Types:
  • Gastropoda: Snails and slugs (most diverse class).
  • Bivalvia: Clams and oysters (filter feeders).
  • Cephalopoda: Include octopuses and squids (highly mobile predators).
• Circulatory System:
  • Mostly open circulatory system with hemolymph; cephalopods have a closed system.

Phylum Annelida (Segmented Worms)

• Characteristics:
  • Body divided into segments, enhancing flexibility and specialization.
• Advantages of Segmentation:
  • Backup for organ systems, regulated hydrostatic skeleton, and specialization of segments.
• Classes:
  • Errantia: Mobile worm-like animals, often predatory.
  • Sedentaria: Includes earthworms and leeches, often more sedentary (include detritivores).

Summary Points

• Focus areas include basic animal classifications, anatomical features, reproduction methods, and ecological roles of the nine animal phyla discussed.
• Important to understand the evolutionary relationships and the significance of morphological adaptations within the animal kingdom.