Arthropods Flashcards
Ecdysozoans
the presents of Ecdysis (moulting)
(Both nematodes and arthropods show ecdysis and have a cuticle)
Cleavage?
NO SPIRAL CLEAVAGE
Example of a protostome without out spiral cleavage
Coelom?
Coelomates, coelom is very reduced.
Metamerically segmented
Body segment = somite
Appendages on segments
Groups of specialised segments are called tagmata (process is tagmosis)
Head → thorax → abdomen (segments separated into these three groups)
Hox genes
Tell cells which segment they are in. developmental genes that control the anterior/ posterior orientation
Different groups of arthropods have the same hox genes
Why is the cuticle so important?
Allows arthropods to be aquatic or terrestrial
Cuticle structure
Epicuticle
Pro-cuticle
→exo & endo cuticle
(The epidermis secretes the cuticle)
Pro-cuticle
Made up of chitin and protein bound together to form a glycoprotein
Exo-cuticle
is ‘Tanned’ = extra cross linkages that form which make it very toughened
Acts as support
Issues with the cuticle
Locomotion is difficult
Circulation
Gas exchange
Excretion
Growth
Issues with the cuticle: Movement
Muscles are attached to the appendages and body
Issues with the cuticle: Circulation
coelom not needed for movement
has become reduced and combined with blood system to create HAEMOCOEL
Contains heart that pumped blood around system
Issues with the cuticle: Gas exchange
Specialised structured
gills and other structures
Issues with the cuticle: Excretion
Specialised enclosed structures
Issues with the cuticle: Growth
Ecdysis
What happens during ecdysis?
- Epidermis secretes new cuticle
- Releases proenzymes (unactivated enzymes)
- Proenzymes become activated and start digesting proteins and chitin found in endocuticle
- Animal uses fluid or air to expand size when cuticle is soft, once cuticle is hardened they can expel fluid/air and grow into cuticle
- Growth starts to slow until moulting - growth happens in jumps
Terrestrial arthropod size limitation
Coconut crab = largest terrestrial arthropod (50cm)
Giant spider crab = largest aquatic arthropod (4m)
aquatic environments can support larger sizes
Compound eye
Made up of ommatidia (up to 4000)
Sensitive to movement over large field of vision - magnification
Visual fields overlap
Poor resolution and image formation
Earliest group of arthropods ?
Trilobites
Trilobite body structure
divided into 3 sections (cephalon, thorax, pygidium)
Metameric segmentation
Biramous appendages - have two branches
Gnathobase
Biramous appendages
Two branches
filamentous (antennae)
Swimming or walking leg
Gnathobase
Grinding surface used to process food
Chelicerates Body structure
only 2 tagmata
Prosoma - top region - cephalothorax
Opisthosoma - bottom region - thorax
Characteristic features of chelicerates
Chelicerae - front appendages
Pedipalps - seconds pair of appendages
Next 4 pairs of walking legs
No antennae, no distinctive head
Extant chelicerates (2 example marine species)
Horseshoe crab
Sea spiders (pycnogonoids)
Horseshoe Crab Body features
Two tagmata (prosoma & Opisthosoma)
Compound eyes
Only chelicerate that has compound eyes
Also has simple eyes
What is special about Horseshoe Crab blood?
- Haemocyanin (blue blood) contains copper
- They are bled because the blood contains
limulus amoebocyte lysate - Blood is able to detect endotoxins
- Used to detect endotoxins present in medicine
- (half a million are harvested every year)
Horseshoe Crab Respriation
Book gills
Horseshoe crab - reproduciton
Dioescious (seperate sexes)
External fertilisation
Mass spawning
Sea Spider Features
Prosoma reduced
Digestive & reproductive organs found on legs
Sea spider Reproduction
Reproductive organs found on legs
External fertilisation
Male shows parental care
Eggs held in place by ovigers (hook like structures on legs)
Larvae are parasitic until developed into adult
What are some forms of terrestrial chelicerates?
Arachnids
Spiders & Scorpions
(ticks and mites are a subclass of arachnids)
Oldest group of Arachnids?
Scorpions
over 400 million years old
Scorpion body structure
- Two body segments (prosoma & opisthosoma / cephalothorax & abdomen)
- Chelicera first pair of appendages
- Pedipalps - second pair of appendages (large pincers)
- Median and lateral eyes
- Pectines: Chemosensory - can detect chemicals
Scorpion sting apparatus
Telson - has photoreceptors
Scorpion respiration
Small entrances on underside lead to book lungs
Scorpion Reproduction
- Dioecious
- Male deposits spermatophore on ground holds female and passes her over the spermatophore
- Indirect internal fertilisation
- Females give birth to live young
- Broods offspring
How are a spider cheliceraes modified?
Modified into fang like structure
Can inject neurotoxins into prey as use as defence
Spider Silk
- Spinnerets - spinning silk - produced by silk glands
- Can produce different types of silk from different silk glands
- Silk is produced for mating, dispersing, webs, wrapping prey, gift presenting etc
- Strong substance
- Made from Fibroin
Spider features
- Prosoma and opisthosoma
- Small waist allows movement
- 4 pairs of eyes
Spider: Digestive system
- Malpighian tubules: attached to gut, allows expulsion of waste products
- Most are carnivorous: enzymes released from fangs digest prey which they then suck back up - external digestion
- One species of veggie spider discovered (Bagheera kiplingi) collects beltian bodies from Acia trees (plant material)
Spider: Reproduction
Fertilisation:
- Internal indirect fertilisation
- Male puts sperm into silk sac then sucks up sac in their pedipalp which he then uses to insert sperm into female
- Sexual dimorphism
- Usually males smaller than females
- Nephila sp extreme difference between sexes
Spider: Stabilimentum
Not clear what it does
Lots of theories
Prey attraction? Mating ritual? warning?
Co-operative spiders
live in large colonies and share food
Feed on large items (co-operatively bring down larger prey)
Ticks and mites
Mites: free-living & parasitic form
Ticks: Ectoparasites
Ticks and mites body structure
Two body sections are less distinguishable from one another
prosoma is known as gnathosoma
Hypostome: used by ticks to anchor onto prey
Ear mites
Vet worked on mites
Awarded ignoble prize
Infected himself with mites
Dust mites
Not parasitic but live in close contact with people
Ticks Lymes disease
Transmitted by bacteria spirochete
Crustaceans Habitat
Mostly aquatic
Mostly marine
Woodlouse is a terrestrial form
Crustaceans body form (Primitive)
Primitive form → head + thorax, appendages all the same
2 pairs of antennae
Crustacean sexes
Mostly dioecious
Nautilus larval stage
Crustacean body form (Variation)
- More variation and radiation in evolved forms
- Differentiation of appendages
- Appendages are biramous - two branches.
- Additional branch can be modified for food capture or respiration
- 2 pair of antennae (characteristic for crustacea)
- 1-3 thoracic appendages may be incorporated into head (maxillipeds)
Types of crustacea: Water Flea (daphnia)
- Two pairs of antennae
- Reduced abdomen
- Uses throaxes appendages for feeding
- Parthenogenetic
- When environmental conditions are harsh they favour sexual reproduction
Types of Crustacea: Barnacle
- Hermaphrodites
- No abdomen
- Dont have abdominal-A hox gene which controls abdomen formation.
- Some species have the largest penis to body ratio found in the animal kingdom
- Penis shape altered depending on environmental conditions
Types of crustacea: Parasitic Barnacles
- Parasitic barnacle (Sacculina)
- Takes over host reproductive organs and controls it
- Can change hosts behaviour
- Disables reproduction so all the crabs energy goes into the parasite instead of reproducing.
2 Types of Myriapods
- Centipedes
- Millipedes
2 tagmata
Centipedes
- Usually predacious
- Maxilliped prehensor - poison claw
- Modified appendages in anterior
- 1 pair of antennae
- Name means ‘hundreds of feet’
- Squashed flat - dorsally ventrally flattened
Millipedes
- Name = ‘thousands of legs’
- Each segment has two pairs of legs
- Most are herbivorous
- Rounded form
- Able to emit chemicals for defence → excrete from repugnatorial glands
myriapod respiration
- Respire via tracheal system
- Air is moved by muscles and diffusion
- Excretion via malpighian tubules
