Comparing Invertebrates

1
Comparing Invertebrates

• Unit VI
• Chapter 29

2
Modern Evolutionary Relationships

• Cladogram indicating the sequence in which
  important invertebrate features evolved

3
Evolutionary Trends

• Specialized Cells, Tissues, and Organs
• The evolution of larger and more complex animals
  involved specialized cells joining together to
  form tissues, organs, and organ systems
• Body Symmetry
• All invertebrates except sponges exhibit some
  type of body symmetry
• Radial cnidarians and echinoderms
• Bilateral worms, mollusks, and arthropods

4
Evolutionary Trends

• Cephalization
• The evolution of a body plan for feeding,
  defense, and other functions was accompanied by
  the trend toward cephalization
• Cephalization is the concentration of sense
  organs and nerve cells in the front of the body
• Invertebrates with cephalization can respond to
  the environment in more sophisticated ways than
  simpler invertebrates

5
Evolutionary Trends

• Segmentation
• Most inverts with bilateral symmetry also have
  segmented bodies specialized for specific
  functions
• Coelom Formation
• A coelom is a body cavity that forms between germ
  layers
• Most complex animal phyla have a true coelom that
  is lined completely with mesoderm

6
Coelom Formation
7
Evolutionary Trends

• Early Development
• In most inverts, the zygote divides repeatedly to
  form a blastula (a hollow ball of cells)
• In protostomes, the opening of the blastula
  (blastopore) develops into a mouth
• Includes worms, arthropods, and mollusks
• In deuterostomes, the blastopore forms an anus
• Includes echinoderms and deuterostomes

8
Form and Function in Inverts

• Feeding and Digestion
• The simplest animals break down food primarily
  through intracellular digestion
• Food is digested in the cells
• More complex animals use extracellular digestion
• Food is broken down outside the cells in a
  digestive cavity and then absorbed into the body

9
Patterns of Extracellular Digestion

• Simple animals such as cnidarians and flatworms
  ingest food and expel wastes through a single
  opening
• More complex animals digest food in a tube called
  the digestive tract
• Food enters mouth
• Wastes leave through the anus
• These are characteristics of a one way digestive
  tract
• Roundworms, annelids, mollusks, arthropods,
  echinoderms

10
Patterns of Extracellular Digestion
11
Form and Function in Inverts

• Respiration
• Respiratory organs have large surface areas that
  are in contact with the air or water
• For diffusion to occur, the respiratory surfaces
  must be moist

12
Aquatic v/s Terrestrial Respiration

• Many aquatic animals respire through their skin
  (cnidarians and flatworms)
• Aquatic mollusks, arthropods, and annelids
  exchange gases through gills
• Spiders respire using book lungs
• In insects, air enters the body through openings
  called spiracles, travels through tracheal tubes
  and then diffuses in and out of surrounding fluids

13
Invertebrate Respiratory Structures
14
Form and Function in Inverts

• Circulation
• Most complex animals move blood through their
  bodies using one or more hearts and either an
  open or closed circulatory system
• OPEN blood is only partially contained within a
  system of blood vessels
• Arthropods and most mollusks
• CLOSED vessels extend throughout the body and
  blood remains contained within these vessels
• Annelids and some mollusks

15
Open v/s Closed Circulatory System
16
Form and Function in Inverts

• Excretion
• Most animals have an excretory system that rids
  the body of metabolic wastes while controlling
  the amount of water in the tissues
• Aquatic ammonia diffuses from the body tissues
  into the surrounding water
• Terrestrial convert ammonia into urea before
  elimination
• In annelids and mollusks, urine forms in
  tube-like structures called nephridia
• Some insects and arachnids have Malpighian
  tubules (saclike organs that convert ammonia into
  uric acid)

17
Form and Function in Inverts

• Response Inverts show 3 trends in the evolution
  of the nervous system
• Centralization in flatworms and roundworms, the
  nerve cells are more concentrated, or centralized
  with a few clumps of ganglia (nerve tissue) in
  the head
• Cephalization in mollusks and arthropods,
  ganglia are organized into a brain at one end of
  the body that controls the nervous system
• Specialization complex animals, such as insects
  and echinoderms, have a variety of specialized
  sense organs that detect light, sound, chemicals,
  and movement

18
Form and Function in Inverts

• Movement Support invertebrates have one of 3
  main kinds of skeletal systems
• Hydrostatic skeleton muscles surround a fluid
  filled body cavity that supports the muscles
• Annelids some cnidarians
• Exoskeleton external body covering made of
  chitin
• arthropods
• Endoskeleton structural support located inside
  the body
• Echinoderms and vertebrates

19
Movement Support in Inverts
20
Form and Function in Inverts

• Reproduction most invertebrates reproduce
  sexually during at least part of their life cycle
• Many, however, may also reproduce asexually
• Sperm and egg may meet in 2 ways
• External fertilization eggs are fertilized
  outside the females body (usually in water)
• Internal fertilization eggs are fertilized
  inside the females body