The Invertebrates
Animalia: The Cambrian Explosion
Number of organisms in the fossil record is increasing
New groups were evolving fast
Bodies were larger
Skeletons and hard parts like shells
Specialized cells also appeared
Different groups of cells became specialized
As animals evolved they became more complex
Specialized cells organized into tissues
Tissues organized to form organs
Organ evolved into organ systems
Animalia: Invertebrates
Animals without a backbone
Many, many invertebrate phyla
Three trends in Invertebrate evolution
Germ layers, Coelom, Segmentation
Invertebrates: Three germ layers
Common ancestors of multicellular animals evolved two distinct cell layers: an ectoderm layer (outside) and an endoderm layer (inside)
Sponges and some jellyfish have these two only
Other jellyfish and all other animals have a middle layer, mesoderm, that develops into muscles and skeletons
Invertebrates: Coelom
The existence of a mesoderm lined cavity inside the body. This is space for organs to grow without being affected by the movement of the body
Look at diagram on page 738 and 741
Invertebrates: Body plan built from segmentation
Body is compartmentalized in segments
Allow increases in size with minimal new genetic information (just repeat what you have)
Segments can be specialized for specific functions
Look at the diagrams on page 738 and 741
Invertebrates: Body plan symmetry
Look at the diagrams on page 738 and 741
Some invertebrates have no symmetry
Some have radial symmetry (body parts repeat around an imaginary line drawn through the center of the body)
Some have bilateral symmetry (animals have identical right and left sides, fronts and backs, upper and lower sides)
Invertebrates: Habitats
Life in fresh water, salt water and on land;
Some live part of their life in water another part on land and vice versa
Survey: 9 phyla of invertebrates
Porifera (sponges)
Simplest of all invertebrates; no symmetry
Cnidaria (jellyfish, sea anemones, hydra)
Mostly salt water, some fresh water, radial symmetry
Platyhelminthes (flatworms)
Simplest animal with bilateral symmetry
Many are parasites
Nematoda (roundworms)
Fist to show a tube like digestive system
Range in size from microscopic to more than a meter long
Mollusca (mollusks, clams, snails, squids)
Most are salt water, some fresh water
Most have shells; octopus (8 tentacles) and squids (10 tentacles) have no shells
Annelida (segmented worms, earthworms)
Live on land and in water
Echinodermata (star fish, sea cucumbers, sea urchins)
Show five-part radial symmetry
Arthropoda (spiders, crustaceans, insects)
THE most successful of all the animals
Jointed appendages and exoskeleton
Lobsters, shrimps and crabs
Invertebrate chordates (sea squirts)
Link between invertebrates and vertebrates
Endoskeleton with a notochord
Invertebrate physiology: Skeletons
Three kinds of skeletons are seen in Invertebrates
Hydrostatic
Muscles surround and are supported by a water filled cavity
No hard structures for muscles to pull against
Diagram on page 814
Exoskeleton
External skeleton, muscles are attached to the inside
Arthropods are the best examples
Made of the carbohydrate chitin (remember from fungus)
All exoskeletons are thin a flexible at the joints
Advantage: very adaptable, very strong
Disadvantage: in order to grow the anima has to molt
Endoskeleton
Located inside the body
Present in sponges and echinoderms
Vertebrate are the best examples
Invertebrate physiology: Digestion
Two strategies:
Digestion inside cells and digestion outside cells
Diagrams on page 784
Inside cells:
1) Intracellular digestion
In sponges, cells filter particles of food in the water, digestion occurs inside the cell, digested products transported to other cells
2) Gastovascular cavity digestion (seen in cnidarians and flatworms)
Food goes into a digestive cavity with only one opening to the outside, food broken down in the cavity, smallest particles taken into the cell, waste eliminated through the opening
Outside cells:
1)Tube within a tube plan, food enters a mouth and exits an anus
Food is digested inside this digestive tract; digested food is adsorbed into the cells
Invertebrate physiology: Internal transport
Two kinds of circulatory systems
1) Open circulatory system
2) Closed circulatory system
Open circulatory system
Blood form the heart is not contained inside blood vessels
Example: insects (page 791)
Blood contacts all the tissues of the body
Closed circulatory system
Blood is contained in a system of closed vessels that pass through various parts of the body and return to the heart
Example: earthworms (diagram on page 792)
Provides more rapid and efficient control of blood flow
Invertebrate physiology: Respiration
Two physiology problems:
1)Surface area needs to be large enough so that gas exchange by diffusion is adequate to support the animal
2)Gas exchange surfaces must be kept wet because gas exchange happens by diffusion only across wet membranes
Diagrams on page 788-790
Adaptations
Worms respire through their skin
Crustaceans have gills
Spiders have book lungs
Insects have trachea (tubes that carry oxygen to each cell)
Invertebrate physiology: Excretion
Purpose is elimination of toxic waste
Closely related to control of water loss
Breakdown of amino acids produces ammonia, which is water-soluble
Elimination of ammonia means losing water
Salt-water animals eliminate ammonia by diffusion into the water
Freshwater flatworms have specialized cells Flame Cells to remove excess water (why??, remember osmosis) and ammonia
Annelids, mollusks, invertebrate chordates have specialized organs to remove ammonia from water, eliminate the ammonia in urine and return most of the water to the organism
Land invertebrates convert ammonia to urea, which can be made more concentrated than ammonia, but is still soluble in water
Insects and some spiders convert ammonia into uric acid, which is removed by organs called Malpighian tubules. Uric acid is excreted as a solid waste. This system conserves the most water.
Invertebrate physiology: Response
Specialized cells for response to the environment are called nerve cells
No matter what the animal, nerve cells look and function pretty much the same
Primitive invertebrate have nets of nerves distributed throughout the body
Some jellyfishes show Centralization where nerve cells are concentrated into a system around certain organs like the mouth
Clumps of nerve cells are called ganglia. Ganglia located near the head result in cephalization, gathering nerve cells in the front of the organism where the animal first senses its environment.
Insects and mollusks show development of ganglia into brains
Nervous system development coincides with the development of specialized sensory cells like eyes.
Invertebrate physiology: Reproduction
All invertebrate are capable of sexual reproduction
Creates and helps maintain genetic diversity