Arthropods Flashcards
How can arthropods be organised?
Protostomes
In the ecdysozoa - undergo ecdysis
What are arthropods evolutionary modified by?
Groups of segments specialised - tagmata (process is known as tagmosis)
Specialisation of appendages
Mediated by hox genes
What are hox genes?
Genes that control the anterior - posterior axis
Hox gene ‘tells’ cells which segment they are in
Most animals have hox genes - debate if sponges do
Dictate where appendages form and the type of appendage
Can suppress appendage development or modify it to create different morphology
Give some features of the cuticle
Helped efficient land colonisation
Epidermis secretes the cuticle
Procuticle is made from exo and endo cuticle
Epicuticle is water proof for land and protects from water in freshwater
Cross-linkage between proteins which increases toughness and rigidity - crustaceans use mineralisation instead
Give some general features of the arthropods
Do not undergo peristalsis for locomotion - muscles attach to the cuticle (apodemes) and work in pairs
Have haemocoel not blood and a heart
Have gas exchange
Have specialised enclosed structures for excretion
Undergo ecdysis for growth as the cuticle prevents body size from increasing so have to shed it to increase the body size
Cuticle at the joints is not as thick
How do arthropods grow?
Epidermis secretes proenzymes
These become active and digest the endocuticle
The cuticle lifts off the animal
Epidermis starts secreting the new cuticle
Sheds the old cuticle when the old and new meet
New cuticle is soft so the animal pumps itself up with air or water - so the new cuticle forms over a larger body and hardens
Releases the air or water and goes back to normal size
Allows space to grow into new cuticle and increases body size
What type of eye do arthropods have? What are the features of this eye?
Compound eye
Made up of ommatidia
Sensitive to movement over a large field of vision - due to visual fields overlapping
Relatively poor resolution and image formation
What are the earliest groups of arthropods? What was their body plan?
Trilobites
3 tagmata - cephalon, thorax and pygidium
Biramous appendages
Unspecialised appendages
Give a brief description of the body plan of a chelicerate
2 tagmata - prosoma (for feeding, sensory, locomotion) and the opisthoma (for digestion, respiration and reproduction)
No antennae
No distinctive head - head and thorax combined into cephalathorax
Appendages = chelicerae, pedipalps (first pair of legs) and walking legs (4 pairs)
What are the terrestrial chelicerates also known as?
Arachnids
Give some features of the scorpions
Chelicera are small in the scorpions - used to grind up food
Pedipalps modified into pincers
Simple eyes - rely more on chemoreception (via pectines)
Book lungs for respiring
Stinging apparatus to inject venom
How do book lungs work?
Lamellae is full of haemolymph
Opens to the outside through a spiracle
Air enters
Get gas exchange over the lamellae
Give an example of scorpion mating behaviour
Male grabs female with pedipalps and walks her around
Male drops a spermatophore
Male directs female over it
She picks it up and internal fertilisation takes place
Give a brief description of a spider body plan
Chelicera have been modified into fangs
Pedipalps are mainly sensory - males use them for sperm transfer
Some have simple eyes, some have complex eyes
Have a tapetum to reflect light back onto the eye
Silk is produced in the silk glands and spun in spinneret (silk protein is known as fibroin)
ALL spiders produce silk
Some have book lungs, some have a tracheal system
What is a stabilimentum?
A thickened area of silk
Could be for attracting prey, deterring predators, mating (true function not known - function is probably species dependent)
How do males transfer sperm in spiders?
Male releases sperm (NOT a spermatophore) onto web
Sucks up sperm into pedipalps
Inserts this into female
Have different ways of displaying they are a mate and not prey to the female
What is the difference between ticks and mites?
Mites - free-living and parasitic
Ticks - ectoparasites
What is the body plan of a tick or mite?
Have fusion of the prosoma and opisthosoma
Have a gnathosoma
What bacterium on ticks causes lyme disease?
Spirochete
What are crustaceans classed under?
The mandibulates
Give a terrestrial crustacean
Woodlouse
What is a unique feature of crustaceans?
2 pairs of antennae
What causes variation amongst the crustaceans?
Tagmatisation
Adaptive radiation of appendages
Give some generalised features of the crustaceans
Has a cephalathorax
Have an abdomen
2 pairs of antennae
1-3 thoracic appendages may be incorperated into the head (maxillipeds)
All have mandibles
Most have compound eyes
Biramous appendages - two branches per leg (exopod and endopod which are both connected to the protopod)
Have gills to respire - come off the legs
Vascularised chamber in land crabs
Most are dioecious
Give some features of a barnacle
Hox gene (Abdominal - A) is lost so have no abdomen
Hermaphrodite - swap sperm via large penises (have the largesr penis to body size ratio in the animal kingdom)
Valves open when the tide is in
Appendages come out to catch food
Give an example of a parasitic barnacle. How does it work?
Sacculina
Grows into the crab body - prevents crab from moulting and destroys the reproductive system of the crab
The male starts to act as a female
When the parasite is ready to spawn/release offspring the crab climbs to a higher area and grooms the brood pouch (like a female) to release parasite eggs
What animals come under the myriapoda?
Centipedes and millipedes
Give some features of the centipedes
Have a head and body region
Have first and second maxilla
First pair of legs are modified into maxilliped (poison claw)
Are predators
Prone to dessication
Dorsally-ventrally flattened
Give some features of the millipedes
Each segment is two segments fused together - so each segment has four legs
Not flattened, more rounded
Herbivorous
Prone to dessication
Noxious to protect from predators - emit hydrogen, cyanide gas and other chemicals (from repugnatorial glands)
What do myriapoda rely on for gas exchange?
Tracheal system
Movement of air is by muscles and diffusion
What do myriapoda use for excretion?
Malpighian tubules
How is the phylum arthropoda split?
Split into two sub-phyla:
- the chelicerates (horseshoe crabs, sea spiders, arachnids (spiders, scorpions, ticks, mites))
- the mandibulates (crustaceans, myripods, true insects (aka pancrustacea or hexapoda)
