Introduction to Animal Biology Flashcards

Vocabulary flashcards covering the characteristics, evolution, and major groups of animals, from sponges to chordates.

Animal

Eukaryotic, multicellular, heterotrophic organisms that digest food internally and lack cell walls.

Invertebrates

A group comprising $95\%$ of all animals.

Colonial flagellated protist

The ancestor from which animals evolved $600–700$ million years ago in Precambrian seas.

Cambrian explosion

An event occurring approximately $~542$ million years ago resulting in rapid diversification where all major animal body plans evolved.

Sponges

The first recognized group of multicellular animals; they lack true tissues.

Radial symmetry

A body plan that is identical around a central axis.

Bilateral symmetry

A body plan where there is only one way to divide the organism into equal halves.

True coelom

A body cavity that allows organs to grow and move independently while fluid cushions the organs.

Choanocyte

Collar cells in sponges that draw water through the organism and capture food.

Cnidarians

The first true predators, characterized by radial symmetry, a gastrovascular cavity, and tentacles with stinging cells.

Polyp

The sessile form of a cnidarian.

Medusa

The floating form of a cnidarian.

Flatworms

Simple bilateral animals and hermaphrodites with an incomplete gastrovascular cavity and a digestive system with one opening.

Cephalization

The development of a head with a brain and sensory organs, which is associated with bilateral symmetry.

Roundworms (Nematodes)

The most diverse group of animals, characterized as cylindrical pseudocoelomates.

Molluscs

An animal group consisting of three major subgroups: gastropods, bivalves, and cephalopods.

Annelids

Segmented worms possessing a true coelom, a closed circulatory system, and a complete digestive tract.

Arthropods

A group with $1$ million known species characterized by an exoskeleton and a segmented body plan, including arachnids, crustaceans, millipedes, centipedes, and insects.

Segmentation

A body characteristic that allows for the division of labor among different body regions.

Ecdysis

The process of molting the exoskeleton.

Insects

Animals with three main body parts (head, thorax, abdomen), $3$ pairs of legs, and $0–1$ or $2$ pairs of wings.

Complete metamorphosis

A developmental process consisting of three stages: larva $\rightarrow$ pupa $\rightarrow$ adult.

Incomplete metamorphosis

A type of development characterized by gradual growth through successive molts.

Echinoderms

Marine animals that lack body segments but have an endoskeleton and a water vascular system.

Chordates

A group defined by four key features: dorsal hollow nerve cord, notochord, pharyngeal slits, and a post-anal tail.

Lancelets and Tunicates

The two chordata groups that are invertebrates yet give rise to vertebrates or share a common ancestor with them.