Video Crash Course: Simple Animals https://www.youtube.com/watch?v=tIfsHPpkSPs

Invertebrate Evolution Essential Question: what are the major trends in invertebrate evolution?

The first multicellular animals Invertebrate fossils date back between 575 and 543 millions of years ago Distinctive flat, plate-shaped Showed little cell specialization or cephalization Lived in shallow seas and some may have had photosynthetic algae living within them

Beginnings of invertebrate diversity A few million years later (Cambrian Period) radically different invertebrates Some animals developed shells, skeletons, and other hard body parts, providing a wealth of fossils Ancestors of most modern animal phyla first appeared

Feeding and digesting Simpler animals break down food primarily through intracellular digestion (food digested inside the cells) Ex. Sponges Complex animals use extracellular digestion (food broken down outside of cells and then absorbed into the body) Ex. Mollusks, annelids, arthropods, and echinoderms Flatworms and cnidarians use both

Feeding and digesting Cnidarians and most flatworms ingest and expel waste through the same opening Complex animals digest food in a digestive tract and expels waste through the anus Specialization of the digestive tract allows food to be process more efficiently

Respiration Respiratory organs have large surface areas that are in contact with the air or water. For diffusion to occur, the respiratory surface must be moist Many simple aquatic animals respire through their skin.

Respiration Complex aquatic animals develop gills (rich in blood vessels that brings blood close to the surface for gas exchange) Terrestrial animals have respiratory surfaces covered in either water or mucus as well as having the air moistened as it travels through the body

Invertebrate Evolution II Essential Question: How do different invertebrate phyla carry out life functions?

Circulation Most complex animals move blood through their bodies using one or more hearts Open circulatory systems- blood is only partially contained within a system of blood vessels. One or more hearts pump blood through blood vessels into a system of sinuses or sponge cavities Ex. arthropods and most mollusks

Circulation Closed circulatory systems- Heart or heart-like organs forces blood through vessels that extend throughout the body. Blood is kept at a high pressure and is more efficient than open circulatory systems Ex. Annelids and some mollusks

Excretion Aquatic invertebrates diffuses ammonia from their body tissues into the surrounding water Terrestrial invertebrates must conserve water so they convert ammonia into a compound called urea which is eliminated through urine

Response (Nervous system) Nerve net- simplest nervous system found in cnidarians that consists of individual nerve cells in a netlike arrangement throughout the body Centralized- in flatworms and roundworms, the nerve cells are more centralized in small clumps in the head Cephalization- in cephalopod mollusks and arthropods, the nerve cells (ganglia) are organized into a brain that controls the nervous system

Response (Nervous system) Complex animals may have a variety of specialized sensory organs that can detect light, sound, chemicals, movement, and even electricity Ex. Flatworms have simple eyespots that detects the presence of light while arthropods have eyes that can detect motion and color, and can forms images

Movement and support Hydrostatic skeletons- muscles surround a fluid-filled body cavity that supports the muscles Ex. Annelids and certain cnidarians Exoskeletons- an external skeleton made of chitin in which muscles are attached inside the hard body Ex. Arthropods and shelled mollusks Endoskeletons- a structural support inside the body Ex. Echinoderms

Reproduction Most invertebrates reproduce sexually, however depending on favorable environmental factors, many may also reproduce asexually (faster than sexually) Hermaphrodites- individuals that produce both sperm and eggs Ex. Earthworms