INVERTEBRATE DIVERSITY SECTION (Biol.201), Spr 2000

Dr. Kathy S. Williams (email kwilliams@sunstroke.sdsu.edu)

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SEGENTATION + an EXOSKELETON ->
DIVERSTIY: ARTHROPODS


The large group of segmented animals with exoskeletons is known collectively as the arthropods and includes the most diverse of
        all animals.     (614-624) * FIG. 48.13  Animal clade

Understand the evolution of arthropods by studying their ancestors & relatives. (615-617)

u Annelids and arthropods share features like segmentation and a nervous system composed of a brain and ventral nerve cord. (976-977,
        * FIG. 48.13 Animal Nervous Systems)

u There are 2 groups intermediate between annelids & arthropods: Onychophorans & Tardigrades
        * Figures of an onychophoran & a tardigrade

Arthropods are highly diverse lineage, due largely to the great adaptability of their jointed exoskeleton.

Development of an exoskeleton was a major evolutionary change in animal body form. (1012)

u incorporates the strong, flexible polysaccharide chitin

u includes jointed appendages

u has limitations What are the advantages / disadvantages of an exoskeleton?

 Another advance seen in arthropods - development of complex visual systems. (996-997,
           * FIG.  49.5 Compound Eye)
 
 
DIVERSITY OF ARTHROPODS
 Trilobites (Trilobita) are an extinct group of arthropods (616-617; * FIG.  33.27 Trilobita)

Most of all living arthropods are classified into one of three major taxa:
       Chelicerata,

       Crustacea, &

       Uniramia (myriapods & insects). (617-624)

*** Focus on
            Body Forms
                                        Exoskeleton/molting
            Respiration
                                        Book lungs
                                        Book gills
                                        Gills
                                        Tracheae
            Excretion
                                        Malpighian tubules
                                        (compare and contrast with protonephridia & metanephridia)

ARTHROPOD DIVERSITY: Chelicerata & Crustacea

Most living arthropods (crabs, lobsters, scorpions, spiders, insects) - classified into one of 3 major taxa: Chelicerata, Crustacea, & Uniramia.

Chelicerata includes Merostomata (horseshoe crabs), & Arachnida (spiders, scorpions, mites, & relatives) (617-618)

            Merostomata (horseshoe crabs) is a "living fossil"

u body form   * FIG. 33.28 Horshoe crab   CLICK HERE FOR HORSHOE CRAB OVERHEAD

u respiratory surfaces
 

 Arachnida (spiders, scorpions, mites, & relatives)  

u body forms   * FIG. 33.29  Arachnids, FIG.  33.30 Spider

u respiratory surfaces  * FIG.   Book lungs   CLICK HERE FOR BOOK LUNG OVERHEAD
 
 

 The Crustacea, with over 40,000 spp., are the dominant marine arthropods. (623-624)   * FIG. Crustacea

         CLICK HERE FOR CRUSTACEA OVERHEAD

Members demonstrate variations in body shapes  
• examples include crabs, shrimp, & lobsters

• also barnacles & pillbugs
 

 Again see how function is related to form  
Exemplified by feeding modifications of barnacles.
* FIG. Barnacles   CLICK HERE FOR BARNACLE OVERHEAD
UNIRAMIA: DIVERSITY to the EXTREME
TERRESTRIAL ARTHROPODS

Uniramia are closely related to Crustacea.

u eye structure   * FIG. 49.5 Compound eyes; ommatidia

u 3-part brain   * FIG. 3-part brain

 and the group contains 2 important classes of primarily terrestrial arthropods,
            the Myriapoda & the Insecta. (618-622)
 
Notable myriapods are the millipedes & centipedes. * FIG. 33.31 Myriapods
u have similar structures for gas exchange, excretion, & sensory input (no compound eyes)

u Chilapoda are active predators & have poisonous fangs.

u Diplopoda are scavengers, without fangs. What does the word ‘diplopod’ signify?
 

 Insects are incredibly abundant & diverse, largely due to a magnificent body plan that allowed insects to colonize unexploited terrestrial habitats. u head, thorax, & abdomen, as adults (* FIG.  33.33 Insect anatomy)

u appendages

u mouthparts

u wings, on most adults

u gas exchange system - spiracles & tracheae (828-830, * FIG.  42.21  Tracheae)

u excretory organs - malpighian tubules (881, * FIG.  44.17 Malpighian tubules)

u development & metamorphosis (* FIG.  33.34  Insect metamorphosis)