Diversity of Animals

Diversity of Animals

• Animals are a diverse group, ranging from tiny sponges to large mammals like whales, mammoths, and lions.
• They share key characteristics, including being multicellular heterotrophs.
• Animal cells lack cell walls, and movement isn't restricted to a single environment.
• Reproduction is mainly sexual.
• Embryonic development shows patterns.
• Energy is stored as glycogen, not starch.
• Animals possess nervous and muscular tissue.

Learning objectives

• Students will identify key evolutionary innovations in animal phylogeny and unchanging traits.
• Students will list and describe key features of animal body plans.
• Students will name synapomorphies of animals.
• Students will compare and contrast asymmetry, radial symmetry, and bilateral symmetry.
• Students will differentiate between acoelomates, pseudocoelomates, and coelomates, with examples of their evolutionary relationships
• Students will differentiate between protostomes and deuterostomes.

General Features of Animals

• Animals are diverse organisms.
• They share common characteristics.
• Animals are heterotrophic.
• They are multicellular.
• Animal cells lack cell walls.
• Movement in most animals isn't restricted.
• Animals reproduce mainly through sexual means.
• Animals have patterned embryonic development.
• Their bodies have energy stored in glycogen.
• They have nervous and muscular tissues.

Characteristics of Animals

• Body symmetry: Asymmetrical, radial, or bilateral symmetry are possible.
• Coelom: Coelomate, acoelomate, or pseudocoelomate animals.
• Embryonic cell layers: Animals can be diploblastic or triploblastic.
• Chordates / Non-chordates: Different body plans exist.
• Organ systems: Include digestive, circulatory, and reproductive systems.
• Segmentation: Show external and internal segments.
• Levels of organization: Vary from cells to tissues to organs and organ systems.

Evolutionary Trend in Body Cavity

• Acoelomates: Lack a body cavity, exemplified by flatworms.
• Pseudocoelomates: Have a pseudocoel (false body cavity) like roundworms.
• Coelomates: Possess a true coelom (body cavity), such as earthworms.

Advantages of Coelom and Pseudocoelom

• The reproductive and digestive organs can evolve more complex shapes and functions.
• Internal organs are cushioned and better protected within the body cavity.
• The body cavity can act as a hydroskeleton, supporting and stiffening soft-bodied animals.
• Movement of internal organs is not disturbed when the gut is suspended.

Evolutionary Trend in Body Plan

• Protostomes: Embryonic development where the mouth develops before the anus.
• Deuterostomes: Embryonic development where the anus develops before the mouth.

Phylum Porifera (Sponges)

• Lack definite symmetry.
• Organised at the cellular level, specialized cells work together.
• Mostly sessile (stationary) organisms, anchored to a surface
• Filter feeders, extracting nutrients from the water.
• Reproduce sexually or asexually, commonly hermaphroditic.
• Composed of a gelatinous matrix, including different cells (choanocytes, pinacocytes, amoebocytes, etc.).
• Important role in nutrient cycles in coral reefs and used in some industries

Phylum Cnidaria (Jellyfish, Corals, etc.)

• Radial symmetry.
• Mostly marine organisms, though some inhabit fresh water.
• Contain specialized stinging cells (nematocysts) for defense and prey capture
• Incomplete digestive system (gastrovascular cavity).
• Mostly have a simple nervous system.
• Can be important in nutrient cycles and some industries

Phylum Platyhelminthes (Flatworms)

• Triploblastic, bilateral symmetry, flattened body plan.
• Acoelomate – lacking a body cavity.
• Internal organs are less developed than in higher animals.
• Some are free-living, others are parasitic.
• Monoecious (hermaphroditic) – possessing both male and female reproductive organs.
• Lack circulatory, respiratory, and skeletal systems.

Phylum Arthropoda

• Triploblastic, bilateral symmetry, segmented body.
• Most diverse animal phylum.
• Live in both aquatic and terrestrial habitats.

Phylum Chordata

• Triploblastic
• Bilateral symmetry
• Includes vertebrates (animals with backbones)

Evolution in Segmentation

• Segmentation involves repeating body units, seen in some animals.
• This structure can include similar, fluid-filled segments.
• Segments are specialized for specific functions
• This allows for more efficient movement, flexibility and specialized functions.

Evolution in Cephalization

• Development of a head region with sensory organs.
• Concentration of nervous tissue at the anterior end.
• Leads to the development of a sophisticated brain.

Evolution in Nervous System

• Neurons in animals function as electrical signaling cells.
• Many animal groups utilize a form of basic nerve net
• Advanced animals have central nervous systems, often with concentrated ganglia (clusters of nerve cells) or brains.

Evolution in Skeletal Modification

• Skeletal systems have evolved in a variety of forms across different animal groups.
• Includes internal skeletons made of substances like collagen.
• Transitions to more complex skeletons are part of animal evolution, allowing for movement or support