Review Sheet -- Test 1 (Week 1) Biology 1224 -- Entomology; James Adams
What is an Insect? See "Classification of Arthropods"
Insects are in the Phylum Arthropoda (meaning "jointed appendages").
(Chapter 16, pages 319 - 323)
Distinguishing Characteristics of Arthropods:
1. Jointed appendages (of course!)
2. An exoskeleton (which must either be shed or added on to for growth)
This exoskeleton provides protection, support and muscle attachment (like your endo-
3. Distinctly segmented body.
Several different subphyla are included in the arthropods (Know the bold faced groups)
Chelicerates which includes Arachnids (spiders, scorpions, ticks, mites, chiggers, etc.)
Crustaceans which includes crabs, lobsters, shrimp, isopods (pillbugs), etc.
Myriapods, which includes centipedes (Chilopoda) and millipedes (Diplopoda)
Hexapods -- this subphylum includes the insects and odd primitive orders
Some people believe Myriapods and Hexapods are sister groups, and put them together into
Distinguishing Characteristics of the Atelocerata:
See "Entomological Terms" handout
1. Mouthparts that include:
a. Labrum (upper "lip")
b. Two pairs of food manipulating mouthparts: mandibles and maxillae
c. Labium (lower "lip")
2. One pair of antennae on head, which is freely moving from other segments
3. Sclerites ("hard parts") on each segment: a top tergite, lateral pleurites, and a sternite
4. Several internal structures:
a. Respiratory system -- with tracheae and spiracles (usually two per segment)
b. Digestive system -- with fore-, mid- (with peritrophic membrane) and hindgut
c. Excretory system -- with Malpighian tubules
d. Circulatory system -- open, with dorsal blood vessel carrying blood forward to head
Among the Classes included in the Atelocerates are:
Diplopoda -- Millipedes, with two pairs of legs per segment
Chilopoda -- Centipedes, with one pair of legs per segment
And the Superclass Hexapoda -- Hexapods, with six legs total; includes the insects
Distinguishing Characteristics of Hexapods:
1. Six legs, of course!
2. Three body parts: head, thorax and abdomen
3. Wings in many (but not all)
All Hexapods used to be called Insects (class Insecta); you'll notice that your book mentions three
separate classes of hexapods -- the Protura, Colembola, Diplura and Insecta . . . Why?
There are good indications that six-leggedness may have arisen independently more than once, or, in
other words, the Protura/Collembola/Diplura compared to the Insecta are in some ways REALLY
different, particularly in the head structure (entognathous bladelike or styliform mandibles with no
basal grinding lobes, and with a single basal connection to head; musculate antennal segments).
Entognathy refers to the mouthparts being retracted (pulled up) inside a pouch in the head, which
probably has to do with protection of the mouthparts in the soil environment they live in. Indeed, in
many respects they are more like myriapods, living in the high humidity litter environment,having
rudimentary abdominal appendages suggesting more legs at some point in their history, and with
indirect insemination. Additionally, the Protura are odd in that they lack antennae and add segments
continuously when they molt (anamorphosis); insects have a set number of segments that doesn't
change as they grow.
In this course, we will talk about ALL hexapods, but don't be surprised if I refer to all of them as
insects from time to time!
Why study Insects, or Who Cares?!
Insects are SUCCESSFUL, in many respects:
1. They are diverse -- many, many different species in the world.
2. They are numerous -- lots and lots of individuals.
3. They have inhabited most parts of the surface of the earth, including being very diverse
in the terrestrial (land) environment.
Why have insects been so successful? (See pages 13 & 14)
1. A multipurpose, largely water impermeable exoskelton, and internalized respiratory
2. Inhabiting the terrestrial environment, particularly having done so before vertebrates
3. A small body size -- minimal survival requirements
4. A fast (short) generation time and tremendous production of immatures (young).
Allows much more rapid evolutionary adaptation and ultimately speciation -- likely
a major reason why insects are so diverse.
5. Flight for the vast majority of species -- allows escape, finding resources and dispersal.
6. Many have complete metamorphosis B reduces competition between life stages.
Still, why study insects? Because they influence YOU.
1. Because they are so abundant, particularly in the terrestrial environment, you WILL
2. There are Beneficial insects -- Examples?
3. There are Injurious insects -- Examples?
We will discuss the impacts of insects on humans in much greater detail later in the semester.