Phylum Arthropoda: Uniramia & Sensory Systems ... - Biosciweb.net

Phylum Arthropoda: Uniramia & Sensory Systems 12.1 

Lab #12 -- Biological Sciences 102 – Animal Biology 

THE MOST DIVERSE GROUP OF INVERTEBRATES 

~ THE INSECTS ~ 

(and similar animal forms) 

Insects and myriapods are a large group of mandibulate arthropods that breathe by means of 

tracheae and are characterized by having uniramous appendages and only one pair of 

antennae. Crustaceans may have uniramous or biramous appendages, but uniramians are 

characterized by having appendages with only one “branch”. There are very few aquatic adult 

forms and nearly all of these are freshwater. Some insect young are aquatic and possess gills, 

but their gills are not homologous to the gills of crustaceans. 

Body Plan Features Retained by Arthropods 

(seen in previously studied phyla): 

‣ bilateral symmetry 

‣ eucoelomic (true coelom) 

‣ high degree of cephalization = well developed head 

‣ segmentation (metamerism) 

‣ triploblastic structure (endoderm, mesoderm and ectoderm) 

‣ all organ systems are present 

Body Plan Features Characteristic of Members of the Phylum Arthropoda: 

1. developed striated muscle for rapid movement 

2. an exoskeleton or cuticle containing the tough nitrogenous polysaccharide chitin 

3. gills or a very efficient tracheal system for gaseous exchange 

4. greater specialization of organs, especially in the function among the appendages 

5. open circulatory system 

Body Plan Features Characteristic of Members of the Subphyla Myriapoda and Hexapoda: 

1. one pair of antennae 

2. uniramous appendages 

3. tracheal system (or gills in larvae) for respirarion 

The term myriapods (Gr. myries, myriad, numberless, + podos, foot) is a common name for 

members of the Subphylum Myriapoda (centipedes, millipedes, and related kin) 

Myriapod characteristics include: 

1. elongate metameric bodies consisting of repeating somites (body segements) 

2. two tagmata (coherently organized body semgents); the head and the trunk 

3. all species are terrestrial and breathe with an efficient tracheal system 

The term insect (in-sek'ta) (L. insectus, cut into) is a common name for any member of the 

Class Insecta; the largest and most diverse of all animal taxa. Together with the Class 

Entognatha (a group of similar but divergent hexapods) they from the Subphylum Hexapoda 

Insect characteristics include: 

1. a body typically divided into three tagmata; a distinct head, thorax, and abdomen 

2. Three pairs of walking legs, six (hex) legs total 

3. usually two pairs of functional (or modified) wings on the mesothorax and metathorax 

4. a respiratory system of tracheal tubes (gills are sometimes present in aquatic young)



Phylum Arthropoda: Myriapod and Hexapod Classification 

Subphylum Myriapoda (Gr. myrios, countless, + podos, feet). The myriapods. 

Class Chilopoda (ki-lop'o-da) (Gr. cheilos, lip, + podos, foot). The centipedes. 

1. characterized by an elongate and dorsoventrally flat body plan 

2. only one pair of appendages per somite 

3. the first pair of legs are modified into venomous forcipules (forceps-like pincers) 

4. almost exclusively carnivorous taxa, predating mostly on smaller invertebrates. 

Class Diplopoda (di-plop'o-da) (Gr. diploos, double, + podos, feet). The millipedes. 

1. characterized by an elongate and subcylindrical body plan 

2. each “diplo-segment” has two pairs of legs (versus the one pair found in centipedes) 

3. largely slow moving detritivores capable of chemical defense through the secretion of 

caustic substances or mechanical defense by curling into a ball 

Subphylum Hexapoda 

Class Insecta (in-sek'ta) (L. insectus, cut into). 

The insects - more than one million species 

Subclass Archaeognatha (Monocondylia) 

Order Archaeognatha – the jumping bristle-tails 

Subclass Dicondylia 

Order Zygentoma – the silverfish. 

Subclass Pterygota – The winged insects 

- 97% of all insects are a member of this subclass - 

Insect growth and metamorphosis 

The immature and adult forms of most insects are strikingly different in the both their 

morphology and ecology, this is evolutionarily selectable as it allows the young to occupy a 

different ecological niche from the adult and thus reduce competition between 

generations. Most immature insects lack wings and must go through a series of molts 

before a final metamorphosis occurs and the flighted sexually mature adult (imago) 

emerges. 

Holometabolous (complete) metamorphosis: the young (referred to as 

larva) are strikingly different from the adults and must undergo a period 

of massive morphological changes, usually occuring in a pupa (also 

called a chrysalis or a cocoon) These species usually have four distinct 

life stages; egg, larva, pupa, and adult, These species are referred to as 

endopterygotes as their wings develop internally. (Endopterygota used 

to be an Infraclass in the Subclass Neoptera and although it has since 

been dissolved its morphological description remains true). 

Hemimetabolous (incomplete) metamorphosis: the young (referred to 

as a nymph or naiads) more or less resemble miniature adults (though 

wingless). Nymphs will undergo a series of molts to become 1 st , 2 nd , 3 rd 

(etc) instars before one final molt after which they emerge as an adult 

imago. These species are referred to as exopterygotes as their wings 

develop externally, these immature wings can be seen as small “wing 

pads” on developing larva. (Exopterygota used to be an Infraclass in 

the Subclass Neoptera and although it has since been dissolved its 

morphological description remains true).



Characterization of Winged Insect Taxonomy 

Note: the following insect orders are exopterygotes; their wings develop externally and they 

display hemimetabolous (incomplete) metamorphosis in which the young resemble 

smaller adults and grow by molting. 

Subclass Pterygota 

Infraclass Paleoptera - “ancient winged” insects (cannot fold wings over abdomen) 

Order Ephemeroptera - mayflies 

Order Odonata - dragonflies and damselflies 

Infraclass Neoptera - “new winged” insects (capable of folding wings over abdomen) 

Order Orthopera - crickets, grasshoppers and katydids 

Order Dermaptera - earwigs 

Order Isoptera - termites 

Order Phasmatodea - walking sticks 

Order Dictyoptera - mantids and cockroaches 

Suborder Mantodea - mantids such as the praying mantis 

Suborder Blattaria - cockroaches 

Order Pthiraptera - sucking and biting lice 

Suborder Anoplura - sucking lice on humans (eg. head lice and pubic lice) 

Suborder Amblycera – biting lice on birds and mammals 

other minor suborders contain sucking/chewing lice on other mammals 

Order Hemiptera - true bugs 

Family Belostomatidae - toe biters and water scorpions 

Family Gerridae - water striders 

Family Corixidae - water boatment 

Family Lygaeidae - seed bugs 

Order Embiidina - web-spinners 

Order Grylloblattodea - ice crawlers, ice bugs 

Order Thysanoptera - thrips, corn flies, thunder flies 

Order Mecoptera - scorpion flies, hanging flies 

Order Plecoptera - stone flies 

Order Psocoptera - book lice 

Order Mantophasmatodea - rock crawlers and gladiators 

Note: the following insect orders are endopterygotes; their wings develop internally and they 

display holometabolous (complete) metamorphosis in which the young enters a pupation 

state to gain the adult form. 


Infraclass Neoptera - “new winged” insects 

Order Coleoptera - beetles (300,000+ species) 

Order Diptera - true flies 

Order Trichoptera - caddis flies 

Order Lepidoptera - butterflies, moths, skippers, and related kin 

Order Hymenoptera - bees, ants, and wasps 

Order Neuroptera - lacewings and their allies 

Order Raphidioptera - snakeflies 

Order Megaloptera - alderflies, dobsonflies, and fishflies 

Order Strepsiptera - twisted winged parasites



Insect Flight Adaptations 

Although some insect species are secondarily wingless (such as ants and termites) most insect 

species have two pairs of fully developed or modified wings; one pair on the metathorax, one 

pair on the mesothorax and never a pair on the prothorax. Wings are highly diverse 

appendages and often differ significantly between insect orders. 

Direct Flight Muscles 

Evolutionarily ancient insect orders such as the odonatids 

(dragonflies and damselflies), ephemeropterans 

(mayflies), and dictyopterans (cockroaches and mantids) 

utilize a basic mechanical system in which thoracic flight 

muscles attach directly to the base of the wings, which flex 

up and down on a single hinge. Direct flight muscles are 

not capable of very high frequency wing beats. 

Indirect Flight Muscles 

Most other winged insect orders utilize an evolutionarily 

more advanced system of indirect flight muscles in which 

the flexing of perpendicular ventrodorsal and longitudinal 

muscles deform the thorax and cause the wings to flex up 

and down as they rotate on a hinge and fulcrum type 

system. These muscles do not associate with the wings 

and flight direction is controlled by minor direct flight 

muscles control the direction and angle of the wings. 

Synchronous Flight 

All direct flight muscles and some indirect flight muscles beat in a synchronous fashion, 

that is, each muscle only contracts once for every nerve impulse. As neurons have a 

refractory period that limits the frequency in their firing, synchronous flight muscles 

likewise have an upper limit on how quickly they beat (usually less than 50 beats per 

second). Examples include butterflies, dragonflies, and grasshoppers. 

Asynchronous Flight 

The layout of indirect flight muscles, allows for a positive feedback system in which 

wings continue to beat between neuronal refractory periods. Since circular and 

longitudinal muscles function by alternately stretching and compressing the thorax 

(instead of connecting straight to the wings), they also alternately stretch each other. 

The contraction of one muscle group stretches the opposing muscle group and 

stimulates a contraction in that group, thus, wing beats are said to become 

asynchronous as each nerve impulse may stimulate several wings beats. Extremely 

high wing beat frequencies (as high as 1,000+ beats per second in some flies) can be 

achieved with this system. Examples include bees, flies, and wasps. 

Tracheal System 

The cellular exchange of oxygen and carbon dioxide in insects is facilitated 

by a tracheal system of open tubes and air pockets that deliver gasses 

directly to the cells. Tracheal tubes originate as invaginations of the insects 

exoskeleton called spiracles, and terminate at individual cells. This 

ventilation system is all topologically exterior to the insect and is shed with 

each molt. Ventilation can be passive but is usually facilitated by muscular 

contractions of the abdomen, forcing air in and out of the tracheal system. 

Unlike higher vertebrates, insects do not transport oxygen in their 

hemolymph (blood), this is one of the major limiting factors to their size.



Sensory Systems – Specialized Sensory Cells & Organs 

Sensory Receptor Cells 

These cells carry information to ganglia or the central nervous system via sensory 

neurons 

‣ thermoreceptors = detect either heat or cold 

‣ mechanoreceptors = detect mechanical changes, ie touch, pressure, muscle stretch, 

sound, etc. 

‣ hair cells = detect sound waves and fluid movement for hearing and equilibrium. These are 

found in the organ of Corti and semicircular canals of the inner ear as well as the neuromast 

cells of the lateral line system in fishes. The statoliths used by many arthropods for 

equilibrium (balance) contains hair cells. 

‣ stretch receptors = monitor changes in muscle length and activity. Stretch receptors 

modulate stretch reflexes that maintain optimal resting muscle length by resisting passive 

changes in muscle length (e.g. patellar tendon stretch reflex). The optimal resting muscle 

length is the length at which the muscle is the strongest. 

‣ chemoreceptors = detect odor (by the nose, antennae, etc.) and taste (by the tongue, feet, 

etc.). Chemoreceptors also detect changes in blood chemistry such as changes in carbon 

dioxide and oxygen in the blood that regulate the rate of respiration. 

‣ Photoreceptors (eg. rods & cones) = detect 

light. The eyespots in flatworms, the ocelli and 

ommatidia (compound eye) of arthropods and retina 

of many animals contains photoreceptors. The 

wavelength of light detected depends on the 

organism. Snakes can detect visible and infrared 

light (heat). Humans can only detect visible light. 

Some insects can see in the ultraviolet portion of the 

electromagnetic spectrum. 

‣ nociceptors (pain receptors) = sense and 

modulate pain response. Indicates danger or injury 

Your instructor will draw a simple reflex arc on the board to describe the integration between 

the sensory nervous system, central processing/integration in the cerebral ganglia or central 

nervous system and the motor system. This is basically how a stimulus causes a response 

in an animal. Draw this reflex arc on page 12.20 at the end of the lab. 

Ideas important in Vertebrates (and maybe invertebrates) 

sensation = a “feeling” or general awareness of stimuli resulting from sensory information 

entering the central nervous system (brain and spinal cord) 

perception = the brain’s meaningful interpretation, or conscious understanding of sensory 

information



LAB PROCEDURE 

NAME: 

LAB SCORE: 

Observation of Living & Displayed Specimens 

‣ Use the textbook and Internet to help you answer the questions – you may 

not be able to determine the answers by only viewing the specimens. 

Subphylum Myriapoda 

Class Chilopoda 

‣ As available, observe one of the chilopod (centipede) specimens and answer the 

following questions using the Internet as a reference. 

‣ Record the descriptive information requested at the end of the lab for this species. 

Centipedes, or "hundred-leggers," are active predators that live in moist places under logs, 

stones, and bark, where they feed on worms, larvae, and insects. Note the general shape of the 

body and arrangement of segments and appendages. 

‣ Is the body circular or flattened in cross section 

Some species have simple ocelli; others have large, faceted eyes resembling the compound eyes 

of insects. 

‣ What is the function of the ocelli in arthropods 

Chilopods have antennae; a labrum, anterior to the mouth; mandibles and first 

maxillae, lateral to the mouth; and second maxillae, bearing a long palp and a short labial 

portion just posterior to the mouth (see diagrams in the lab). 

The first trunk appendages are the prehensile maxillipeds, each bearing a terminal poison 

fang. 

‣ Do the rest of the trunk segments bear legs 

The last segment bears the gonopores, and the anus is located on a short telson. In Lithobius 

they are located near the bases of the legs. In Scolopendra the spiracles are located more 

dorsally and are present on alternate segments. 

‣ What is the function of the spiracles in centipedes




Class Diplopoda 

‣ As available, observe one of the diplopod (millipede) specimens and answer the 

following questions using the Internet as a reference. 

‣ Record the descriptive information requested at the end of the lab for this species. 

Millipedes, or "thousand-foot worms," are found throughout the world, usually hiding in damp 

woods under bark, leaves, rocks, and logs. They are herbivorous, feeding on decaying wood or 

leaves. Their most distinguishing feature is the presence of diplosegments, which are double 

trunk segments probably derived from the fusion of two single segments and each bearing two 

pairs of legs. The name "Diplopoda" comes from Greek diploos, double, and pous, podos, foot. 

The gonopores open on the third trunk segment at the bases of the legs. 

‣ How does this compare with the centipede 

The dorsal overlapping of the exoskeletal plates provides full protection for the animal, even 

when rolled into a ball. Each of the diplosegments has two pairs of spiracles. 

‣ Are there appendages on the first trunk segments 

‣ How many pairs on the next three segments 


Class Insecta 

‣ Observe the various insect specimens on 

display, taking particular note of the order to which 

each insect belongs. 

‣ Record the descriptive information requested at 

the end of the lab for each order. 

Among the chief characteristics of insects are three pairs of walking legs; one pair of antennae; 

a body typically divided into head, thorax, and abdomen; and a respiratory system of tracheal 

tubes. Most insects are also provided with one or two pairs of wings. Their sense organs are 

often specialized and perhaps account for much of their success in the competition for 

ecological niches. Most insects are less than 2.5 cm long, but they range from 1 mm to 20 cm, 

with the largest insects usually living in tropical areas. A grasshopper has a fairly typical 

insect body plan. A honey bee, on the other hand, has become specialized for particular 

conditions. Not only is its morphology modified for special functions and adaptations, but it is 

a social insect in which patterns of group organization involve different types of individuals and 

division of labor.




Class Insecta 

Order Dictyoptera 

Suborder Blattaria 

Study of a Living Cockroach 

‣ Each group of students should look at one of the living cockroach specimens. 

‣ We will perform the observations below together as a class. 

‣ Does your cockroach exhibit positive or negative phototaxis What is phototaxis 

‣ Briefly describe the righting response in your cockroach. 

‣ Is this species capable of flight Are there cockroaches that do not fly 

‣ How does the cockroach breathe (How does it get air into its body) 

‣ What are some common foods for cockroaches 

‣ Do not euthanize your cockroach. 

‣ Please return them live to the container provided.



DISSECTION 


Class Insecta 

Order Orthoptera 

Romalea sp. (Lubber Grasshopper) 

Use a dissecting scope for your investigation. 

Obtain one preserved grasshopper specimen for each two students. 

‣ Examine the external anatomy of the grasshopper on both the dorsal and 

ventral sides and be able to identify the structures described below. 

Locate three tagmata: head, thorax, and abdomen 

‣ Is the grasshopper segmented throughout, or is segmentation more apparent in certain 

regions of the body If so, where is segmentation more apparent. 

The chitinous exoskeleton is secreted by the underlying epidermis. It is composed of hard 

plates, called sclerites, which are bounded by sutures of soft cuticle. 

The Head of the Grasshopper 

The head of the grasshopper is freely movable. Notice the compound eyes, antennae, and 

three ocelli, one dorsal to the base of each antenna and one in the groove between them. Lift 

the movable, bilobed upper lip, or labrum (lip), and observe the toothed mandibles (jaws). The 

mouth contains a membranous hypopharynx for tasting food. The bilobed lower lip, or 

labium, is the result of the fusion of the second maxillae. The labium bears on each side a 

three-jointed labial palp. Between the mandible and labium are paired maxillae (jaws) each 

with a maxillary palp, flat lobe, and toothed jaw. Note how the mouthparts are adapted 

for biting and chewing. 

Generally, the insect head has four pairs of true appendages: antennae, mandibles, 

maxillae, and labium (fused second maxillae). There are at least six segments in the head 

region, although some of them are apparent only in the insect embryo. 

‣ After you have studied the rest of the external features, if time permits, you may 

use forceps and probing needles to carefully remove all the mouthparts and arrange them 

in their relative positions on a sheet of paper. 

Head Structures 

‣ compound eyes 

‣ antennae 

‣ three ocelli 

‣ antennae 

‣ labrum 

‣ labium (second maxillae) 

with labial palps 

‣ maxillae with maxillary 

palps 

‣ mandibles 

‣ hypopharynx



Thorax of the Grasshopper 

The thorax is made up of three segments: prothorax, mesothorax, and metathorax, each 

bearing a pair of legs. The mesothorax and metathorax also bear a pair of wings. 

Spiracles (external openings of the insect's tracheal system) are located above the legs in 

the mesothorax and metathorax. Note the leathery forewings (on the mesothorax) and 

the membranous hindwings (on the metathorax). 

‣ Which set of wings is more useful for actual flight 

‣ What appears to be the chief function of the forewings 

The small veins in the wings, or tracheal tubes, are used by entomologists in the 

identification and classification of insects. These transport air to cells in the wings. 

Examine the grasshopper's legs and identify the basal coxa (L., hip); small trochanter 

(Gr., ball of hip joint); large femur; slender, spiny tibia; and five-jointed tarsus with two 

claws and a terminal pad, the arolium 

Which pair of legs is most specialized, and for what function 

Thoracic Structures 

‣ prothorax 

‣ mesothorax 

‣ metathorax 

‣ two pairs of wings 

‣ tracheal tubes in wings 

Leg Structures 

‣ basal coxa 

‣ trochanter 

‣ femur 

‣ tibia 

‣ tarsus 

‣ claws



Abdomen of the Grasshopper 

There are 11 segments in the abdomen of the grasshopper. Notice the large tympanum, 

the organ of hearing, one located on each side of the first abdominal segment. 

‣ On which of the abdominal segments are the paired spiracles located 

In both sexes, segments 2 to 8 are similar and unmodified, and segments 9 and 10 are 

partially fused. 

The eleventh segment forms the genitalia (secondary sex organs). On each side behind the 

tenth segment is a projection, the cercus (pl. cerci; Gr. kerkos, tail). In females the posterior 

end of the abdomen is pointed and consist of two pairs of plates, with a smaller pair between, 

with the whole forming the ovipositior. Between the plates is the opening of the oviduct. 

The end of the abdomen in males is rounded. 

What is the sex of your grasshopper specimen 

Abdominal Structures 

‣ tympanum 

‣ fusion of segments 9 & 10 (if visible) 

‣ cercus 

‣ in females: the ovipositor (if visible) 

‣ Your instructor will be reviewing the grasshopper structures with you under the 

instructor’s dissecting scope. 

‣ You should be able to identify the structures listed in preparation for the 

invertebrate lab practical. 

‣ Place the grasshopper and all dissected parts into the waste container provided. 

‣ Rinse your dissecting tray and clean your supplies and return them.



Displayed Specimens Data 


Class Chilopoda (centipedes) 

Scientific name (if known): 

Common name: 

Notes & observations to help you remember and distinguish this class: 


Class Diplopoda (millipedes) 


Common name: 

Notes & observations to help you remember and distinguish this class:




Class Insecta 

Subclass Dicondylia 

Order Zygentoma (silverfish) 


Common name: silverfish 

Unique structures or features this subclass: 


Class Insecta 


Insect Orders 

Use the taxonomic key provided at the end of the lab to help you review the difference 

between these various insect orders 

Order Ephemeroptera (mayflies) 

Unique structures or features this order: 

Type of mouthparts & typical food: 

Order Odonata (dragonflies & damselflies) 


Type of mouthparts & typical food:



Order Orthoptera (grasshoppers, crickets, katydids, etc.) 



Order Dermaptera (earwigs) 



Order Plecoptera (stoneflies) 



Order Isoptera (termites) 





Order Phthiraptera (lice) 

Suborder Amblycera (biting lice on birds and mammals) 



Order Phthiraptera (lice) 

Suborder Anoplura (sucking lice on human/mammal hair – head/pubic) 



Order Hemiptera (true bugs, cicadas, hoppers, aphids, scale insects, etc.) 



Order Hemiptera (true bugs) 

Family Notinectidae (backswimmers) 

Family Corixidae (water boatman) 

Family Belostomoatidae (toe biters) 

Family Gerridae (water striders) 

Unique structures or features the Family Gerridae (water striders) specifically: 




Order Neuroptera (dobsonflies, ant lions, lacewings) 



Order Coleoptera (beetles, “fireflies”, weevils) 



Order Lepidoptera (butterflies, moths) 



Order Diptera (true Flies - one pair of wings, one pair of halteres for balance) 

Mosquitoes and House Flies among many others are different species of dipterans 





Order Trichoptera (caddis flies) 



Order Siphonaptera (fleas) 



Order Hymenoptera (ants, bees, wasps) 



Order Phasmatodea (stick insects or walking sticks) 






Suborder Mantodea (mantids such as the praying mantis) 




Suborder Blattaria (cockroaches) 



Order Psocoptera (barklice and booklice) 



Order Mecoptera (scorpionflies) 





Homework – use the Internet to assist you in answering these questions: 

‣ Briefly describe and/or draw a diagram to show the lifecycle of an insect that 

undergoes holometabolous metamorphosis (complete metamorphosis). 

‣ Briefly describe and/or draw a diagram to show the lifecycle of an insect that 

undergoes hemimetabolous metamorphosis (incomplete metamorphosis). 

‣ Briefly describe the caste system and various members of any typical ant colony.



LABORATORY NOTES: 

DRAW A DIAGRAM OF A REFLEX ARC IN THE NERVOUS SYSTEM HERE:

Phylum Arthropoda: Uniramia & Sensory Systems ... - Biosciweb.net

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