Animal Evolution – The Invertebrates

Flashcards on Animal Evolution and Invertebrates, covering topics from body plans and symmetry to various phyla and adaptations.

Heterotroph

Organisms that obtain energy and carbon from organic compounds.

Invertebrates

Animals without a backbone; the overwhelming majority of animal species.

Tissue

Cells of a particular type and function, organized in a specific pattern.

Ectoderm

The outermost tissue layer in an animal embryo.

Endoderm

The innermost tissue layer in an animal embryo.

Mesoderm

The middle tissue layer in a three-layered animal embryo.

Body Symmetry

The arrangement of body parts in relation to a central axis.

Asymmetrical

Lacking a defined body symmetry, as seen in sponges.

Radial Symmetry

Body plan in which body parts are arranged regularly around a central axis, like in jellyfish and hydras.

Bilateral Symmetry

Body plan in which the left and right halves are mirror images, common in most animals.

Cephalization

Concentration of nerve cells at the head end in bilateral animals.

Gut

Digestive sac (incomplete digestive system) or tube (complete) that opens at the body surface.

Coelom

A body cavity lined by mesodermal tissue.

Pseudocoel

A body cavity that is partially lined by mesodermal tissue.

Acoelomates

Animals that have no body cavity.

Protostomes

Bilateral animals in which the first opening in the embryo becomes the mouth.

Deuterostomes

Bilateral animals in which the first opening in the embryo becomes the anus.

Closed Circulatory System

A circulatory system in which the heart pumps blood through a continuous vessel system.

Open Circulatory System

A circulatory system in which blood leaves the vessels.

Segmentation

The division of an animal body into repeated units along its length.

Choanoflagellates

Collar-shaped protists that are the closest living relatives of animals.

Placozoans

Simplest known animals, lacking body symmetry, tissues, and organs.

Sponges (Phylum Porifera)

Simple animals that attach to surfaces, lack true tissues, and filter water through pores with collar cells.

Hermaphrodite

An individual that produces both eggs and sperm.

Larva

A free-living, sexually immature stage in the life cycle that develops into an adult.

Cnidarians (Phylum Cnidaria)

Radially symmetrical animals with two tissue layers, including jellyfish and sea anemones.

Medusae

Bell-shaped cnidarians that drift, like jellyfishes.

Polyps

Tubular cnidarians with one end attached to a surface, like sea anemones.

Nematocysts

Stinging organelles in cnidarian tentacle cells, used in feeding or defense.

Nerve Net

Simple nervous system in cnidarians consisting of interconnecting nerve cells.

Hydrostatic Skeleton

Fluid-filled structure moved by contractile cells in cnidarians.

Flatworms (Phylum Platyhelminthes)

Animals with a three-layer embryo, organ systems, but no coelom.

Pharynx

Muscular tube connecting the mouth with the gut in flatworms.

Nerve cords

Two lines of communication along the length of the body in flatworms.

Ganglia

Cluster of nerve cell bodies (simple brain) in flatworms.

Annelids (Phylum Annelida)

Segmented worms with a coelom; typically with chaetae.

Chaetae

Chitin-reinforced bristles on annelids.

Mollusks (Phylum Mollusca)

Bilaterally symmetrical animals with a reduced coelom, mantle, and radula.

Mantle

The outer tissue layer of mollusks that covers internal organs and secretes a shell.

Radula

A feeding structure in mollusks.

Cephalopods

Mollusk group includes squids/octopus, fast and smart, closed circulatory system.

Rotifers (Phylum Rotifera)

Tiny bilateral animals with a pseudocoelom, closest to annelids and mollusks.

Tardigrades (Phylum Tardigrada)

Tiny bilateral animals with a coelom that molt; related to roundworms and insects.

Roundworms (Phylum Nematoda)

Unsegmented, pseudocoelomate worms with a secreted cuticle that is molted.

Arthropods (Phylum Arthropoda)

Most diverse animal phylum with jointed legs and a hardened exoskeleton.

Exoskeleton

A hardened outer covering that provides support and protection.

Chelicerates

Arthropods without antennae, including spiders and horseshoe crabs.

Crustaceans

Mostly marine arthropods with two pairs of antennae.

Myriapods

Arthropods with two antennae and many body segments, including centipedes and millipedes.

Insects

Arthropods with a three-part body plan: head, thorax, and abdomen.

Echinoderms (Phylum Echinodermata)

Spiny-skinned marine invertebrates with a water-vascular system.