Lab 20: Subphylum Uniramia – the terrestrial mandibulates

I. Video: “Alien Empire: Episode 2 – Battlezone/Metropolis” (50 min)

II. Phylum Arthropoda, Subphylum Uniramia

A. Members of the subphylum Uniramia are arthropods & share the general characteristics of all arthropods (that were mentioned last lab)

B. Distinguishing characteristics of the subphylum Uniramia

1. One pair of antennae (remember - chelicerates have no antennae, crustacea have 2 pairs)

2. Appendages are “uniramous” – only one branch in appendage

3. Tracheal system is used for respiration (Fig. 20-19; overhead 87)

a) The trachea are a system of highly-branched tubules for the distribution of respiratory gases

b) Openings to the outside world are called “spiracles”

4. Excretion carried out by “Malpighian tubules” (Fig. 20-20; overhead 87)

a) Malpighian tubules are blind tubules attached to the hindgut of the animal

(1) Malpighian tubules float in the hemolymph within the hemocoel

(2) Excretory products are moved from the Malpighian tubules into the gut

(a) Excretory products are eliminated with the feces

III. The Uniramia are divided into the myriapods (centipedes & millipedes) and the insects

A. Name myriapod means myriad (lots & lots) legs

B. Distinguishing characteristics of the myriapods

1. Two “tagmata” (body regions): head & body

2. Paired appendages on all or most body segments

3. One pair of eyes

4. One pair of antennae

5. One pair of mandibles

6. One or two pairs of maxillae

C. Class Chilopoda – centipedes

1. Body characteristics

a) Have up to 177 segments

b) Dorsalventrally flattened

c) One pair of legs per segment

(1) Exceptions: first segment has poison claws & last two segments lack legs

d) One pair of spiracles per segment

2. Habitat – moist terrestrial habitats

3. Feeding: predators that kill prey with poison from fangs

a) They chew up the prey with mandibles

D. Class Diplopoda (two-footed) – millipedes

1. Body characteristics

a) Cylindrical body

b) Two pairs of legs per segment

c) Two pairs of spiracles per body segment

2. Many millipedes produce nasty defensive secretions (Prof. Wood of HSU’s Chemistry Dept. has isolated several of these)

3. Habitat – dark, moist terrestrial habitats

4. Feeding: herbivorous – feed on decaying plants

IV. Class Insecta – the insects (these are not myriapods)

A. Insects are the most successful group of animals on the planet

1. There are estimated to be 8 to 10 million species

B. They are found in every terrestrial & freshwater habitat – no marine forms

C. Body Characteristics (Figs. 20-4a, 20-8; overhead 85)

1. Three tagmata (head, thorax, abdomen)

a) Head

(1) One pair of compound eyes in adults

(a) Usually 3 ocelli (ocelli are nonimageforming photoreceptor organs)

(2) One pair of antennae

(3) Mouthparts (Fig. 20-18 [grasshopper identical to Fig. 15-3 in lab manual]; overhead T73)

(a) Labrum (upper lip) – not a modified appendage

(b) One pair mandibles (this & below mouthparts are modified appendages)

(c) One pair maxillae

(d) Labium – functions as lower lip

(e) Tongue-like hypopharynx (not labeled on overhead, but is top region of labium)

(f) Mouthparts can be highly modified in shape for different modes of feeding

b) Thorax (back to overhead 85)

(1) Consists of 3 segments: prothorax, mesothorax, metathorax (anterior to posterior)

(2) Each thoracic segment possess one pair of walking legs

(3) Meso- & metathorax each bear a pair of wings in most adults

(a) Some primitive insects are wingless & some others have lost theirs secondarily

(b) Flies have highly modified the rear wings in a plumbbob-shaped structures called a halteres (used to maintain equilibrium during flight)

(4) Leg regions (use Fig. 20-8 – the bee): coxa, trochanter, femur, tibia, metatarsus, tarsus

(a) Be sure to see these on the grasshopper & cricket

c) Abdomen

(1) Possesses 9 to 11 segments

(2) No appendages in adults

(a) Larvae (e.g. caterpillars), may possess prolegs on abdominal segments

(3) Some insects possess sensory structures called cerci (very sensitive to air movement – help insect avoid predators)

(a) Cerci are well developed in crickets

D. Circulation: open circulatory system – details are similar to crustacea

1. Hemolymph is not involved in gas exchange (trachea do that)

E. Reproduction

1. Sexes separate

2. Internal fertilization – therefore, they have to mate

F. Growth

1. Insects need to molt to grow

2. The stage between successive molts is called an “instar”

a) Different species differ in the number of instars they go through prior to becoming adult

3. Insects have three major life history patterns

a) Ametabolous insects look like miniature adults – they just get larger with each molt

(1) This is a primitive state & is found in springtails & silverfish

b) Hemimetabolous (half change) insects have wings that are absent or underdeveloped in juvenile instars

(1) Examples: grasshoppers, crickets, cockroaches, dragonflies

c) Holometabolous (complete change) insects have larval instars that are very different from adults

(1) Larval forms are often wormlike (grubs, caterpillars, maggots, etc.)

(2) Larval instars are followed by a nonfeeding pupal stage, where the insect remodels its body, develops wings & other adult structures

(3) Examples: caterpillars & butterflies/moths, maggots & flies, grubs & beetles

V. Things to do

A. Examine the lubber grasshopper Romalea for external anatomy

B. Lots of demos

C. Dissection of cricket

1. We’ll anesthetize the crickets with carbon dioxide – catch cricket & put it in cooler with dry ice for 5 minutes

2. Cut off legs & wings with fine scissors

3. For the following, use a dissecting microscope

a) Piece of wood next to scope in storage cabinet is used to steady “cake pan” dissection pans

4. Conduct the functional observations listed on page 235

5. To dissect:

a) Put animal ventral side down on dissecting pan (make sure you can see it through the scope)

b) Put 4 pins through the extreme edges of animal

(1) One pair of pins though the prothorax & other pair through posterior abdomen

c) Use sharp scalpel (or very fine scissors) to open animal on dorsal midline

(1) We’ll have some fine scissors to assist if needed

(2) As you open females, a bunch of eggs may come out wound (look like rice grains)

d) Reposition pins to open animal up

(1) Do not stretch the animal laterally as you do this – what you are going for is how thing appear in Fig. 15-9A of lab manual

e) Put a drop or two of saline in body cavity (helps the organs to float & thus are easier to see)

f) Find the internal organs as identified in the manual

(1) Pay special attention to the anatomy of the gut (Fig. 15-9B)