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.

• Specialized Tissues: Most animals have tissues specialized for different functions (e.g., muscle, nerve).

• Other features: Sexual reproduction is common, but not universal; most animals develop from a blastula and gastrula stage.

Animal Development

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

• Key stages: Blastula (hollow ball of cells), Gastrula (formation of germ layers), Organogenesis (organ formation).

Introduction to Invertebrates (Ch. 33)

Major Invertebrate Groups

• Porifera (sponges)

• Cnidaria (corals, jellyfish, etc.)

• Lophotrochozoa (worms, snails, etc.)

• Ecdysozoa (lobsters, insects, etc.)

• Echinodermata (sea stars, etc.)

Main Topics about Invertebrates

• Defining characteristics of vertebrates and invertebrates

• Major vertebrate and invertebrate groups

• Evolutionary relationships between groups

• Key adaptations of each group

Animal Phylogeny

Clades and Relationships

• 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 clades: Deuterostomia, Lophotrochozoa, and Ecdysozoa.

Phylum Porifera (Sponges)

Key Features

• Basal animals, lack true tissues and organs.

• Filter feeders: Water flows through pores into a central cavity (spongocoel) and out through an opening (osculum).

• Cells: Choanocytes (collar cells) generate water flow and capture food; Amoebocytes digest food and distribute nutrients.

• Hermaphroditic: Most sponges produce both eggs and sperm.

Phylum Cnidaria (Corals, Jellyfish, etc.)

Body Plan and Features

• Diploblastic (two germ layers), radial symmetry, no coelom.

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

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

• Specialized cells: Cnidocytes contain nematocysts (stinging organelles).

• Simple nerve net and contractile cells.

• Reproduction: Both sexual and asexual (budding).

Major Clades

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

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

Lophotrochozoans (Worms, Snails, etc.)

General Features

• Highly diverse clade, identified by molecular data.

• Most are triploblasts, have a coelom, and a digestive tract with two openings.

Key Groups

• Flatworms (Phylum Platyhelminthes): Acoelomates, gastrovascular cavity with one opening, flat body, simple excretory system (protonephridia), hermaphroditic.

• Planarians: Free-living, have eyespots and a simple nervous system.

• Flukes (Class Trematoda): Parasitic, complex life cycles with multiple hosts.

• Tapeworms (Class Cestoda): Parasitic, lack digestive system, absorb nutrients through body surface.

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

• Lophophorates: Include Ectoprocta and Brachiopoda, possess a lophophore (crown of ciliated tentacles), true coelom, mostly sessile.

Examples and Applications

• Planarians are used in regeneration studies due to their remarkable ability to regrow lost body parts.

• Tapeworms are important in medicine as human and animal parasites.

Table: Comparison of Major Invertebrate Groups

Group	Symmetry	Tissues	Body Cavity	Key Features
Porifera	None	No true tissues	None	Filter feeders, choanocytes
Cnidaria	Radial	Diploblastic	None	Cnidocytes, gastrovascular cavity
Lophotrochozoa (Flatworms)	Bilateral	Triploblastic	Acoelomate	Flat body, protonephridia
Lophotrochozoa (Rotifers)	Bilateral	Triploblastic	Pseudocoelomate	Alimentary canal, parthenogenesis
Lophophorates	Bilateral	Triploblastic	Coelomate	Lophophore, sessile

Additional info:

• Invertebrates are highly diverse due to their long evolutionary history, adaptation to various ecological niches, and the development of novel body plans and reproductive strategies.