Animal Diversity and Invertebrate Phyla: Study Guide (Ch. 32 & 33)

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.

• Heterotrophic Nutrition: Animals obtain nutrients by ingesting other organisms.

• Specialized Tissues: Most animals have tissues that perform specific functions (e.g., muscle, nerve tissue).

Features Not Common to Most Animals

• Asexual reproduction is not a feature common to most animals; sexual reproduction is predominant.

• Development into a fixed body plan, specialized tissues, and heterotrophic nutrient sourcing are common features.

Embryonic Development

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

• Key stages: zygote → blastula → gastrula → organogenesis.

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.)

Animal Phylogeny Overview

• All animals share a common ancestor (unity in life).

• Animals form a clade called Metazoa (Kingdom Animalia).

• Sponges are basal animals (branch from the base of the animal tree).

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

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

• Bilateria divides into three clades: Deuterostomia, Lophotrochozoa, and Ecdysozoa.

Phylum Porifera (Sponges)

Key Features

• No true tissues, no coelom.

• Filter feeders (suspension feeders).

• Hermaphrodites: Most species have both male and female reproductive organs.

• Sponges are eukaryotic, multicellular, and ingest/digest food, but lack muscle and nerve cells.

Phylum Cnidaria (Corals, Jellyfish, etc.)

Body Plan

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

• Gastrovascular cavity: Digestive compartment with a single opening (mouth/anus).

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

• Radial symmetry, no coelom.

• Simple nerve net and contractile cells; carnivorous.

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, star corals).

Lophotrochozoans

General Features

• Most are triploblasts (three germ layers).

• Most 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): Alimentary canal (two openings), hemocoel, parthenogenesis (asexual reproduction), some sexual reproduction.

• Lophophorates: Includes Ectoprocta and Brachiopoda, with U-shaped alimentary canal, true coelom, exoskeleton, mostly sessile.

• Molluscs (Phylum Mollusca): Diverse group including snails, clams, squids, and chitons.

Body Plan of Molluscs

• Muscular foot (locomotion)

• Visceral mass (internal organs)

• Mantle (tissue that may secrete a shell)

• Ciliated larval stage called a trochophore

Major Mollusc Classes

• Gastropoda: Snails and slugs; most have a single, spiraled shell.

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

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

• Polyplacophora (Chitons): Eight dorsal plates, use foot as suction cup, scrape algae with radula.

Examples and Applications

• Periwinkle snails: Shell thickness increases in response to predation by green crabs (evolutionary adaptation).

• Ammonites: Extinct shelled cephalopods, ancestors of modern squids and octopuses.

Body Plan Table: Molluscs

Structure	Function
Muscular foot	Locomotion
Visceral mass	Houses internal organs
Mantle	Secretes shell, forms mantle cavity
Radula	Feeding (scraping food)

Additional info: The notes above are expanded with academic context for clarity and completeness, including definitions, examples, and a summary table for mollusc body plans.