Animal Diversity and Invertebrate Phyla (Ch. 32 & 33) – Study Notes

Introduction to Animal Diversity

Domains of Life

• Bacteria, Archaea, and Eukaryota are the three domains of life.

• Animals belong to the domain Eukaryota.

Characteristics Common to Animals

• Multicellularity: Animals are composed of multiple cells.

• Heterotrophy: Animals obtain nutrients by ingesting other organisms (heterotrophic nutrient sourcing).

• Specialized Tissues: Most animals have specialized tissues (e.g., muscle and nerve tissue).

• Additional info: Most animals reproduce sexually, but asexual reproduction is not a universal feature.

Animal Development

• During embryonic development, unique cell layers develop into specific tissues or organs during the gastrula stage.

• Germ layers (ectoderm, mesoderm, endoderm) form during this stage and give rise to all tissues and organs.

Animal Body Plans

• Most animals develop into a fixed body plan, but some can change form (e.g., through metamorphosis).

• Animals are classified based on symmetry (radial or bilateral), presence of tissues, and type of body cavity (coelom).

Introduction to Invertebrates

Major Invertebrate Groups

• Porifera (sponges)

• Cnidaria (corals, jellyfish, sea anemones)

• Lophotrochozoa (worms, snails, molluscs, annelids, etc.)

• Ecdysozoa (lobsters, insects, nematodes, arthropods)

• Echinodermata (sea stars, sea urchins, etc.)

Animal Phylogeny

Key Clades

• Metazoa: The animal clade (Kingdom Animalia), all animals share a common ancestor.

• Eumetazoa: Animals with true tissues (excludes sponges).

• Bilateria: Animals with bilateral symmetry and three germ layers (triploblasts).

• Bilateria is divided into three major clades: Deuterostomia, Lophotrochozoa, and Ecdysozoa.

Phylum Porifera (Sponges)

Features of Porifera

• No true tissues and no coelom.

• Filter feeders (suspension feeders): Capture food particles from water.

• Hermaphrodites: Most individuals produce both eggs and sperm.

• Sponges are basal animals in the animal phylogeny.

Phylum Cnidaria (Corals, Jellyfish, Sea Anemones)

Body Plan

• Two main forms: Polyp (sessile) and Medusa (motile).

• Diploblasts: Two germ layers (ectoderm and endoderm).

• Radial symmetry, no coelom.

• Gastrovascular cavity: Single opening serves as mouth and anus.

• Simple nerve net and contractile cells; carnivorous lifestyle.

Major Clades of Cnidaria

• Medusozoans: Alternate between polyp and medusa stages (e.g., jellies, sea wasps).

• Anthozoans: Only polyp stage, often with exoskeleton (e.g., sea anemones, corals).

Lophotrochozoans

General Features

• Most are triploblasts (three germ layers), have a coelom, and a digestive tract with two openings.

Major Groups

• Flatworms (Phylum Platyhelminthes): Acoelomates, gastrovascular cavity with one opening, flat body, protonephridia for excretion.

• Rotifers (Phylum Syndermata): Microscopic, alimentary canal (two openings), hemocoel, parthenogenesis (asexual reproduction).

• Lophophorates: Include Ectoprocta and Brachiopoda, have a lophophore (feeding structure), true coelom, mostly sessile.

• Molluscs (Phylum Mollusca): Diverse body plans, including muscular foot, visceral mass, mantle, and often a shell. Classes include Gastropoda (snails, slugs), Bivalvia (clams, oysters), Cephalopoda (squid, octopus), and Polyplacophora (chitons).

• Annelids (Phylum Annelida): Segmented worms, coelomates, closed circulatory system.

Body Plan of Molluscs

• Muscular foot for movement.

• Visceral mass contains internal organs.

• Mantle covers the visceral mass and may secrete a shell.

• Larval stage called trochophore.

Classes of Molluscs

• Gastropoda: Snails and slugs, usually with a single, spiraled shell.

• Bivalvia: Clams, oysters, mussels, scallops; two-part shell, filter feeders.

• Cephalopoda: Squid, octopus, nautilus; reduced or absent shell, closed circulatory system, complex brain.

• Polyplacophora: Chitons, eight dorsal plates, use radula to scrape algae.

Example Table: Major Invertebrate Groups and Key Features

Group	Key Features
Porifera	No true tissues, filter feeders, hermaphrodites
Cnidaria	Diploblasts, radial symmetry, gastrovascular cavity
Lophotrochozoa	Triploblasts, coelom, diverse body plans
Mollusca	Muscular foot, visceral mass, mantle, shell (often)
Annelida	Segmented body, closed circulatory system

Additional info: This summary covers the main animal phyla and their evolutionary relationships, as well as key anatomical and developmental features relevant to General Biology students.