Compare and Contrast Invertebrate Classes According to the Following Systems:

Nervous system:  gathers information from the environment, processes it, and allows the animals to respond to it.  The simplest nervous system; the nerve net (cnidarians & primitive flatworms) consists of individual nerve cells that form a netlike arrangement throughout the body.  Three evolutionary trends in nervous systems:  1. centralization 

2. cephalization  increases with complexity most bilaterally symmetrical animals have cephalization  3. specialization  in general the more complex the animal the more highly specialized its sense organs.

Respiratory system:  in order to supply oxygen to & remove CO₂ from their tissues animals must exchange these gases with the environment.  Diffusion of the gases into & out of the animal’s body requires a thin moist membrane that maximizes surface area in contact with the air or water. Gas exchange surface must be kept moist.  Terrestrial (land) animals keep the respiratory surface moist with water or mucus.  Air is also moistened as it passes through the body to the respiratory structures.

Excretory system:  multicellular animals must regulate the amount of water in their tissues.  Fresh water animals must excrete excess water taken in by osmosis.  Terrestrial animals and some marine animals must reduce water loss.  All animals must get rid of nitrogenous wastes.  Nitrogenous wastes contain nitrogen, are toxic and are produced by cellular metabolism.  The breakdown of amino acids produces ammonia, which is highly toxic.  Most aquatic invertebrates excrete ammonia because the water environment dilutes it to safe levels.   Terrestrial animals must get rid of the ammonia at the same time conserving water.  Many convert ammonia into urea, which is less toxic than ammonia but also soluble in water. The urea is excreted in urine.  Some terrestrial animals convert nitrogenous wastes to uric acid, less toxic than ammonia and also less soluble in water.  It forms a paste.

Circulatory system:  supplies cells with oxygen and nutrients and carries away cellular (metabolic) wastes for excretion.  Two types of circulatory systems:  Open Circulatory System – blood is not contained within blood vessels, it bathes the tissues and then is moved back to the heart.  Closed Circulatory System – blood remains completely contained within a network of blood vessels that extend throughout the body.  Materials diffuse through blood vessel walls.  It is a more efficient distribution of blood.

Digestive system:  necessary to breakdown food into usable components.  Two types of digestion:  Intracellular Digestion – food is broken down inside the cells.  Extracellular Digestion – food is broken down outside the cells in a digestive tract, allows animals to eat and digest food larger than their cells.   Simple digestive systems consist of only one body opening, a mouth.  It is inefficient because food and wastes are entering and leaving through the same opening.  More advanced organisms have a complete digestive system with both a mouth and an anus.  This arrangement is called a tube-within-a-tube body plan.  More advanced animals have specialized regions of the digestive tract.

Reproductive system:  two types of reproduction:  Asexual Reproduction – nonsexual means of reproduction which can include grafting and budding and fragmentation.  Budding is when an organism grows off the body of a parent organism.  Fragmentation is when pieces of an organism can grow into a complete organism.  Asexual reproduction involves only one parent.  The offspring are identical to the parent (clones).  Asexual reproduction does not increase genetic diversity. 

Sexual Reproduction – the process where two cells (gametes – sex cells, sperm & egg) fuse to form one hybrid, fertilized cell.  Sexual reproduction produces offspring genetically different from both parents.  Sexual reproduction increases genetic diversity.  Many animals are hermaphrodites – contain both male & female reproductive organs.  Most hermaphrodites do not self-fertilize.  Why?  For sexual reproduction to occur the two cells must come together. This is called fertilization.  There are two types of fertilization:  External Fertilization – the two cells usually sperm and egg are released from the body and unite outside the body.  This type of fertilization requires the release of large numbers of sperm and eggs and a water medium to transport the gametes.  Internal Fertilization – the two cells unite inside the body of the female. This is a more efficient method, requiring fewer gametes to ensure fertilization and allowing for fertilization to occur on land.  The water environment is within the female’s body.

EMBRYOLOGICAL DEVELOPMENT OF ANIMALS

1.  zygote – fertilized egg

2.  blastula – hollow ball of cells, formed by mitosis (cleavage) in the zygote

3.  gastrula – layered structure formed by gastrulation – indenting of the blastula at the

                      blastophore

gastrulation forms germ layers:  ectoderm – outer layer forms body coverings

                                                    endoderm – inner layer forms body linings

                                                    mesoderm – middle layer forms muscles and organs

Protostomes – mouth forms from blastopore

Deuterostomes – anus forms from blastopore

Acoelomates – body cavity not surrounded by mesoderm

                         2 layered acoelomates

                         3 layered acoelomates

Pseudocoelomates – body cavity only partially surrounded by mesoderm

Coelomates – body cavity completely surrounded by mesoderm

       

1.  Phylum Porifera –  sponges – sessile organisms (can’t move) often are filter feeders

                                                     and hermaphrodites

                                    Acoelomates

                                    Symmetry:  asymmetrical

• Class Demospongia
• Class Hexactinellida
• Class Calcarea
• Class Sclerospongia

All lack true tissues and organs.

Nervous system: 

Respiratory system: gases are exchanged through the water by diffusion

Excretory system:  diffusion of nitrogenous wastes in the form of ammonia

Circulatory system:  nutrients and oxygen move into cells and wastes move out by

                                 diffusion

Digestive system:  filter feeders, specialized cells trap & digest food (choanocytes or

                              collar cells), amoebocytes distribute the food throughout the sponge,

                              wastes leave through the osculum, this is intracellular digestion

Reproductive system:  asexual reproduction – budding, gemmules (harsh conditions)

                                                                          fragmentation

                                     sexual reproduction – external fertilization,  many are

                                                                         hermaphrodites (contain both male and

                                                                         female reproductive organs)

                                                                         hermaphrodites usually do not self fertilize

                                                                        (why?)

2.  Phylum Cnidaria – hydra, jellyfish, corals and anemones

                                    tentacles with cnidocytes (stinging cells) with nematocysts

                                   (stingers) that inject neurotoxins

                                    show polymorphism ( 2 body forms)  polyp – sessile & medusa –

                                    free-swimming

                                   Symmetry:  radial symmetry – body parts arranged around a central

                                                                                    point  

• Class Hydrozoa – hydra   
• Class Scyphozoa – jellyfish
• Class Anthozoa – corals and anemones

Nervous system:  hydrozoans have a nerve net – can detect stimuli but don’t detect the

                            direction of the source

                            scyphozoans have a centralized nervous system

Respiratory system:  respiration is by diffusion; all are aquatic and only a few cell layers

                                  thick

Excretory system:  waste are removed by diffusion

Circulatory system: nutrients and oxygen move through cnidarians by diffusion

Digestive system:  simple digestive system with only one opening, the mouth and a

                              gastrovascular cavity where food is broken down, digestion is

                              completed in the cells in intracellular digestion

Reproductive System:  hydrozoans may reproduce asexually by budding or sexually

                                      There may be separate sexes or they may be hermaphrodites

                                      Fertilization is external

                                      Most scyphozoans have separate sexes

                                      Anthozoans may reproduce sexually or by budding

Life cycle of a jellyfish:  Male free-swimming medusa releases sperm.  Female free-swimming medusa traps sperm in folds of tissue around mouth.  Eggs are fertilized.  Zygote develops into a ciliated, free-swimming, planula larva.  The planula larva finds a good spot to land, and forms a sessile polyp.  The polyp forms a stack of medusae in an asexual process called strobilation.  The medusae are released one at time. This is an example of what?

3.  Phylum Platyhelminthes – flatworms

                                                Symmetry:  bilateral – a line through only one plane

                                                                                     produces mirror images

• Class Turbellaria – planarians most free living
• Class Trematoda – flukes most are parasites
• Class Cestoda – tapeworms internal parasites

Nervous system:  turbellarians have a ladder like nervous system with longitudinal and

                             transverse nerve cords. They have a centralized nervous system.  They

                             have cephalization with 2 anterior ganglion.  They have photosensitive

                             eye spots.  Parasitic flatworms do not have much need for a nervous

                             system.

Respiratory system:  respiration is through the skin by diffusion, only a few cell layers

                                  thick (flatworms)

Excretory system:  flame cells get rid of excess water, ammonia diffuses through body

                              surfaces

Circulatory system:  nutrients, gases, and wastes move by diffusion because they are only

                                 a few cell layers thick (flatworms)

Digestive system:  free living flatworms have a simple digestive system with only one

                              body opening, the mouth. They also have a tube-like pharynx.

                              Digestion is intracellular.

                              Tapeworms have no digestive system because they are surrounded by

                              digested food and only need to absorb it.

Reproductive system:  free living flatworms reproduce sexually and most are

                                    hermaphrodites.  They also reproduce asexually by fission.

                                    They are capable of regeneration.

                                    Most flukes are hermaphrodites but some species have separate

                                    sexes.

                                    Tapeworms are hermaphrodites that reproduce sexually.

Life cycle of a tapeworm: 

1. cow eats grass with tapeworm eggs
2. eggs hatch
3. larvae burrow into muscles
4. larvae form bladder worms
5. humans eat under cooked beef
6. bladder worms are released
7. bladder worms form scolex (head with hooks and suckers)
8. scolex attaches to intestine
9. proglottids (hermaphroditic reproductive segments) develop behind scolex
10. proglottids and eggs are released with feces of the host

4.  Phylum Mollusca – Mollusks

                                     Symmetry:  bilateral symmetry

                                     Trochophore larva shows relationship to annelids                                             

§         Class Bivalvia (Pelecypoda) – clams, oysters, scallops (hatched footed mollusks)

§         Class Cephalopoda – squid, cuttlefish, octopus, nautilus (head footed mollusks) (tentacles)

§         Class Gastropoda – snails, slugs (stomach footed mollusks)

§         Amphinura – chitons

§         Monoplacophora – show segmentation and a relationship to annelids

Nervous system:  complexity varies greatly

                             Clams:  sessile inactive filter feeders

                                          simple, with a few ganglia and nerve cords, sense organs such

                                          as chemical and touch receptors, statocysts (simple organs for

                                          balance), ocelli (simple eyes that detect light and movement

                                          but do not form images)

                            Cephalopods:  active predators

                                                    cephalization

                                                    Highly developed nervous system, well-developed brain,

                                                    best invertebrate eyes, may be more intelligent than

                                                    some vertebrates

                            Gastropods:  stalked eyes, olfactory tentacle

 Respiratory system:  Aquatic mollusks have gills

                                  Terrestrial mollusks have a primitive lung formed by the mantle

                                  cavity

Excretory system:  nephridia – remove ammonia from the blood and release it to the

                                                 outside

Circulatory system:  Bivalves and gastropods have open circulatory systems with hearts

                                 Cephalopods have closed circulatory systems with hearts

Digestive system:  complete digestive system (tube-within-a-tube plan) two openings

                              (mouth and anus) digestive system becomes more specialized into

                               regions as animals become more advanced (pharynx, esophagus,

                               stomach, intestine)

                               gastropods: have a radula a rasping tongue

                               cephalopods: radula modified into a beak

                               extracellular digestion – food larger than cells is digested in a

                                                                      digestive tract

Reproductive system:  Bivalves – most separate sexes with external fertilization – must

                                                      release large numbers of eggs and sperm

                                     Cephalopods – internal fertilization 

                                     Gastropods – internal fertilization many are hermaphrodites

5.  Phylum Nematoda – nematodes

                                       Symmetry:  bilateral symmetry

Digestive system:  complete digestive system, many parasites, some free-living

6.  Phylum Rotifera – rotifers

                                   Symmetry:  bilateral symmetry

Digestive system:  complete digestive system, microscopic

7.  Phylum Annelida – annelids

                                     Symmetry:  bilateral symmetry

• Class Polychaeta – bristle worms, many setae and parapodia
• Class Oligochaeta – earthworms, a few setae and no parapodia
• Class Hirudinea – leeches no setae or parapodia

Nervous system:  earthworms have a brain formed by two ganglia and a ventral nerve

                            cord

Respiratory system:  Polychaetes and leeches have gills

                                  Oligochaetes respire through skin or gills if aquatic

Excretory system:  nephridia – tubelike structures take in body fluids, remove nitrogenous

                                                wastes in the form of urine and return fluids and

                                                compounds to body

Circulatory system:  closed circulatory system – blood retained in blood vessels

                                  Earthworms have 5 aortic arches which pump blood and a dorsal

                                  and ventral blood vessel

Digestive system:  complete digestive system – tube-within-a-tube plan

                               Earthworms have the following regions:  mouth, pharynx, esophagus,

                               crop (stores food), gizzard (grinds food), intestine (absorbs nutrients),

                               anus

                               Leeches feed on blood and have an anesthetic and an anticoagulant

                               Used to reattach limbs

Reproductive system:  many are hermaphrodites including earthworms, but do not self-

                                     fertilize. Most have internal fertilization except for feather duster

                                     worms which are sessile.

8.  Phylum Arthropoda – largest animal phylum; more than 95% of all animals are

                                         invertebrates; 3/4^ths of animals are arthropods; arthropoda

                                         means jointed foot; arthropods have a segmented body;

                                         exoskeleton of  chitin;  Advantages of exoskeleton: protects,

                                         prevents water loss, provides a point for muscle attachment to

                                         allow for movement.

                                         Disadvantages of exoskeleton:  limits size, heavy, must be shed

                                         to grow ( molting or ecdysis) making individual vulnerable

                                         Symmetry:  bilateral

v     Subphylum Chelicerata – chelicerae – appendages modified into claws fangs

§         Class Arachnida – spiders, scorpions, ticks, chiggers

§         Class Meristomata (Xiphosura – horseshoe crab

v     Subphylum Crustacea – crayfish, lobster – cephalothorax (fused head and thorax)

                                                                          and abdomen

v     Subphylum Uniramia

§         Class Chilopoda – centipedes – 1 pair of legs per segment, carnivores,

                                                         poison claws

§         Class Diplopoda – millipedes – 2 pairs of legs per segment, herbivores

§         Class Insecta – insects – 3 body segments: head, thorax, & abdomen;

                                              3 pairs of legs attached to thorax; wings if present

                                              attached to thorax

Nervous system:  brain and double ventral nerve cord

                             ganglia along the nerve cord control various body segments

                             chelicerates have pediplaps which function in feeding, reproducing,

                             sensing (chemical receptors) and moving

                             some have compound eyes which form a mosaic image

                             some have ocelli; some have both; insects can see UV light

                             tympanic membranes (eardrums) for hearing

                             crustaceans have statocysts

                             sense of taste well developed

                             sense of smell through antennae and legs

Respiratory system:  spiders have book lungs (folds of tissue) Why?

                                  horseshoe crabs have book gills

                                  lobsters and crayfish have gills

                                  many insects have tracheal tubes

                                  spiracles are the openings that allow air to enter the body to both the

                                  tracheal tubes and book lungs

Excretory system:  Malpighian tubules – absorb fluid from the blood in body sinuses,

                               concentrating nitrogenous wastes in the form of uric acid and then

                               adding them to food wastes in the intestine

                               some aquatic arthropods excrete through their gills

                               crustaceans have green glands for excretion

Circulatory system:  open circulatory system with usually one heart to pump blood

Digestive system:  complete digestive system

Reproductive system:  separate sexes with internal fertilization

                                    metamorphosis – series of developmental changes

                                    2 types of metamorphosis:

                                     Complete metamorphosis:  egg, larva, pupa, adult ex: butterfly

                                     Incomplete metamorphosis:  egg, nymph, adult ex: grasshopper

                                     advantage of metamorphosis:  reduces competition between

                                     young and adult

9.Phylum Echinodermata

                                        Symmetry:  adult:   radial,   larvae:  bilateral

• Class Crinoidea – sea lilies
• Class Asteroidea – starfish
• Class Ophuiroidea – brittle stars
• Class Echinodea – sea urchins
• Class Holothuroidea – sea cucumbers

Water vascular system:  water enters through the madreporite (sieve plate), passes

                                        through the stone canal, into the ring canal, into the radial

                                        canals, into the tube feet which consist of a bulb and sucker

                                        the water vascular functions in feeding, respiration, internal

                                        transport, excretion and movement

Nervous system:  nerve ring that surrounds the mouth and radial nerves that extend down

                            each arm

                            sensory cells that detect chemicals are scattered over the body

                            light sensitive cells form eye spots at the tip of each arm

                            some posses statocysts

Respiratory system:  tube feet form the main gas exchange surface and some species have

                                  skin gills

Excretory system:  excrete ammonia through the tube feet and skin gills

Circulatory system:  because tube feet and skin gills are scattered all over the body a

                                 system to bring wastes to these structures and take oxygen  from

                                 them is not necessary

                                 nutrients are distributed by digestive glands and body cavity fluid

Digestive system:   the starfish inverts its stomach through its mouth into a clam and

                               partially digests the clam in the clam’s own shell, then brings the

                               partially digested clam into back into its body and digestion is

                               completed by digestive glands, feces leave through the anus which is

                               on top of the starfish (aboral surface)

                               Sea lilies are filter feeders

                               Sea cucumbers are detritus feeders

Reproductive system:  most have separate sexes, there are some hermaphrodites

                                     external fertilization

                                     regeneration:  a section of the central disk of  a starfish will

                                     produce a starfish (asexual reproduction)