Download Invertebrate Evolution

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