Chapter 27 Study Guide: Early Animal Evolution

These flashcards cover key concepts related to the evolution of early animals, including the characteristics of sponges and cnidarians, and significant events during the Cambrian explosion.

Ediacaran biota

A group of self-sustaining organisms with no skeletons that represent the transition from simple microscopic forms to more complex forms.

Bilateral symmetry

A characteristic of animals with two openings (mouth and anus), such as those appearing during the Cambrian period.

Sponges

Filter-feeding animals that are asymmetrical and lack true tissues.

Choanocytes

Flagellated collar cells in sponges that capture food particles from water.

Cnidarians

Symmetrical animals with tentacles that have a non-centralized nerve net and a gastrovascular cavity with a single opening (mouth = anus).

Cambrian explosion

A period marked by the rapid diversification of life, development of vision, and increased availability of minerals, resulting in the extinction of Ediacaran fauna.

Gastrovascular cavity

A digestive compartment with a single opening, found in Cnidarians and other early animals.

Osculum

The opening in sponges through which water exits after being filtered.

Spongocoel

The central cavity in sponges where water is filtered.

Benthic

Organisms that live on the ocean floor, contrasting with those found in the water column.