Arthropods Flashcards
What are some common characteristics of arthropods?
Bilateral symmetry. Chitinous, segmented exoskeleton. Ventral nervous system. Open dorsal circulatory system. Tracheal respiratory system/book lungs.
What are the layers of the exoskeleton?
Epicuticle, exocuticle, endocuticle, gland cells and epidermis.
Describe the general circulatory system in arthropods.
Hemocoel filled with hemolymph.
Heart = dorsal muscle tube pumping anteriorly.
Heart is perforated by paired ostia with one-way valves.
How does gas exchange differ between chelicerates/true crustaceans and insects?
Chelicerates/True crustaceans exchange O2 at gills or book lungs.
Insects perform gas exchange using a tracheal system.
Describe the anatomy of compound eyes.
They are made up of many ommatidia with each containing a cornea, lens and photoreceptor cells.
What is the arrangement of the tracheal system in arthropods?
Spiracles > Trachea > Tracheoles
How is the arrangement of the tracheal system kept in place?
The tracheal tubes are stiffened with bands of chitin.
What is the arrangement of the excretory system in arthropods?
Mouth > Crop > Gastric ceca > Stomach > Malphigian tubules > Rectum
In what form is nitrogenous waste excreted?
In true crustaceans = ammonia.
In terrestrial arthropods = uric acid.
What is the body plan for chelicerates?
1) Prosoma/Cephalothorax (fused head + thorax).
2) Opisthosoma/Abdomen.
How does the body plan of mites differ to typical chelicerates?
Mites have no visible division between the 2 segments.
What are the appendages on the front of the mouth of chelicerates known as?
Chelicerae. They usually take the form of pincers. In spiders they are fangs.
What are the respiratory systems in chelicerates?
Marine chelicerates have gills.
Terrestrial chelicerates have book lungs + tracheae or just tracheae.
How is the nervous system arranged in chelicerates?
Ganglia are generally fused into large masses in the prosoma.
What is the limb order in chelicerates?
Chelicerae, pedipalps and then 4 pairs of legs.
What is the telson?
Posterior-most division of the body of an arthropod.
What are chelicerae used for?
Grasping + subduing prey.
Injecting gut enzymes.
Defence.
Processing prey/plant material.
What are pedipalps?
They resemble legs as seen in spiders or form massive pincers in scorpions.
What are the segments of a chelicerate’s legs?
Coxa > Trochanter > Femur > Patella > Tibia > Metatarsus > Tarsus > Claws
How do the legs of chelicerate’s differ to those of insects?
Arachnids possess a patella unlike insects.
Why do spiders have 2 sets of claws on their legs?
1 pair to grip the ground.
1 pair to grip the silk of the web.
What are scopulae and how do they function?
Dense tufts of hair beneath the claws. They provide adhesion for climbing using Van der Waals forces.
What form of eyes do chelicerates possess?
Ocelli (simple eyes) except for horseshoe crabs which possess compound lateral eyes. All chelicerate eyes lack a lens.
How many eyes do spiders have?
8 in 4 pairs.
Describe the circulatory system of spiders.
Heart + aorta with the heart lying in the pericardium which is linked to the book lung.
Describe the circulatory system of mites.
Some mites have no heart. Instead they use cuticular diffusion.
Describe the respiratory system of chelicerates.
A system of tubular tracheae + a single “spiracle”. Not homologous to insect tracheae. Book lungs are used for gas exchange in larger chelicerates.
What are book lungs?
Internal surface of lamellae providing a large area for GE. Up to 4 pairs in scorpions, up to 2 pairs in spiders.
Where do spiders and scorpions produce enzymes?
In the gut.
Where do ticks and mites produce enzymes?
In the salivary glands.
What parts of the gut are contained within the foregut in chelicerates?
The mouth, pharynx and oesophagus.
What parts of the gut are contained within the hindgut in chelicerates?
The nephridia and malpighian tubules.
What are the 3 main classes of chelicerates?
Arachnida (arachnids), merostomata (horseshoe crabs) and pycnogonida (sea spiders).
What are the 2 main classes of myriapods?
Chilopoda (centipedes) and diplopoda (millipedes).
What is the body plan for myriapods?
1) Head.
2) Elongated trunk (no division between thorax and abdomen).
Describe the sensory organs of myriapods.
1 antennae pair on head. Simple lateral eyes (loosely scattered ommatidia).
What are the 2 forms of anal legs?
Antenniform (sensory) and pincer like (aggressive/defensive).
What gives the class chilopoda its name?
A pair of forcipules - pincer like forelegs. Chilopoda means ‘lip-foot’.
Why are myriapods only found in moist environments?
They cannot close their spiracles and possess a permeable integument.
How many pairs of legs do chilopods and diplopods have per segment?
Chilopods have 1 pair of legs per segment whilst diplopods have 2 pairs of legs per segment.
How does locomotion differ between chilopods and diplopods?
Chilopods use an alternating gait whilst diplopods possess a symmetrical gait.
What are some defences possessed by diplopods?
Drab colouration, rolling into a ball/spiral, stink glands, caustic secretions, sedative secretions and toxicity.
Where does the term crustacean come from?
‘crusta’ refers to the calcified exoskeleton.
What is the carapace of a crustacean?
A mantle-like fold of the body wall from the last head segment bearing the maxillae. It may be fused with some/all segments covered.
What segments make up the cephalothorax of a crustacean?
The thorax and head.
What are biramous legs and what are some benefits of them?
Crustacean legs have an exopod and endopod forming 2 branches. This allows for increased modification and variation.
What occurs before moulting in crustacea?
Prior to moulting, calcium is absorbed and deposited into the new cuticle.
Why have crustacea been unsuccessful on land?
They lack a waxy cuticle to prevent water loss and rely on gills for respiration - gills are inefficient out of water. All crustacea have an aquatic larval stage.
Which group of crustaceans have successfully colonised the land? Why is this?
Isopoda (woodlice). They possess pleopodal lungs which act like spiracles. They are still limited to moist areas.
What is the body plan for insects?
1) Head.
2) Thorax.
3) Abdomen.
What are the benefits of a tracheal respiratory system?
It provides a large cuticular area for GE.
Spiracles possess closing valves to prevent water loss.
Tracheae branch into musculature.
How do larger insects increase the efficiency of their tracheal respiratory system?
Larger insects utilise the active pumping movements of the abdomen to ventilate the outer tracheae.
Is the circulatory system in insects open or closed?
Open.
What is transported in the hemolymph in insects?
Nutrients, salts, waste, hormones etc.
What are some defensive roles of hemolymph?
Clotting, pathogen encapsulation and sequestration of distasteful chemicals.
What are the 3 cavities of the hemocoel in insects?
Pericardial, perivisceral and perineural sinuses. They are divided by the dorsal and ventral diaphragms.
How is musculature arranged in insects?
Muscles attach to the exoskeleton’s inner surface through tonofibrillae (fine connecting fibrils).
What are apodemes?
Ridges at the attaching site of the legs to strengthen the inner cuticle.
Are insect skeletal muscles synchronous or asynchronous?
Synchronous - one contraction per nerve impulse.
Are insect flight/tymbal muscles synchronous or asynchronous?
Asynchronous - more than one contraction per nerve impulse.
What is the function of the foregut in arthropods?
Ingestion, storage and grinding.
What is the function of the midgut in arthropods?
Excreting digestive enzymes and digesting/absorbing food.
What is the function of the hindgut in arthropods?
Absorbing water, salts, amino acids and sugars.
What is the peritrophic membrane and its function?
A thin semi-permeable sheath that compartmentalises digestion, ensheaths the food and acts as an infection barrier.
How do you calculate the ovigeny index (OI)?
Initial egg load X No. of eggs ready to lay / Lifetime potential fecundity
What does a high ovigeny index show?
Highly predictable oviposition site availability.
What does a low ovigeny index show?
Less predictable oviposition site availability.
What is parthogenesis and what are the benefits of this reproductive strategy?
Producing clones. There are zero time and energy costs for gamete production and courtship.
What are the 4 main methods of insect flight?
Gliding flight, flapping flight, downwash and wake capture.
Describe insect wing structure.
No muscles/tendons in the wings.
2 layers of exoskeleton ‘sandwiched’ together.
Girder system of tubular ‘veins’.
What are the 2 mechanisms of flight generation in insects?
Direct and indirect flight
Which insect groups use direct muscle flight?
Dragonflies, damselflies and mayflies.
Which insect groups use indirect muscle flight?
All members of neoptera.
How does direct muscle flight?
Up + down wing movement is caused by the contraction of muscles connecting the wing base to the thorax ‘floor’. Each wing has independent power from 2 antagonistically acting muscles.
What are the pros and cons of direct muscle flight?
Pro: wings do not have to beat in unison.
Con: wing beat frequency limited to 25bps (rate of nerve impulses going to muscles).
How does indirect muscle flight?
Horizontal + vertical muscle set act on the thorax (not wings). Thorax ‘roof’ is less flexible. When muscles contract the whole thorax ‘box’ changes shape (states switch).
What is the main advantage of indirect muscle flight?
It overcomes the constraint of wingbeat frequency.
Why do most indirect muscle fliers use asynchronous muscles?
They allow higher wing beat frequency as they automatically contract after extension.
What are halteres and what is their role in insect flight?
Small club-shaped organs that provide information to the insect by acting as gyroscopes.
What flight fuel is used by hymenoptera and diptera?
Carbohydrates.
What flight fuel is used by grasshoppers, aphids and migratory insects?
Lipids in sustained flight; carbohydrates in short-duration flight.
