L10 Arthropods Flashcards
What evolutionary lineage are the arthropods in?
Protostoma, ecdysozoa
What is a feature shared by all arthropods?
Metameriaclly segmented, Pair of appendages each segment
How are arthropods specialised?
Groups of segments becoming specialised
Appendages specialised
Hox genes
What is tagmatisation?
Groups of adjacent metameres join into larger functional units, magma, responsible for specialised tasks
What is the role of hox genes in the arthropods?
First discovered in the arthropods
Control the anterior-posterior axis
How genes ‘ tell’ cells which segments they are in
Highly conserved between the arthropods
Difference between groups due to differential gene expression
What is the hypothesis as to how the arthropod body plan arose?
Gene duplication event of two unusual hox genes, ubx and abd-A
What is the cuticle?
Exoskeleton that completely covers the body, made by cross linkages in glycogen and protein, allows for life on land, but probably evolved for protection
Describe locomotion in the arthropods
Rigid exoskeleton provides points of attachments for appendages, but cannot move via peristalsis. Muscles are used for appendages
Describe circulation in the arthropods
Have a haemocoel. which is a coelom combined with the circulatory system, open system. Heomolymph propelled through body by the heart, convergent with molluscs
Describe gas exchange in the arthropods
Body impermeable. Aquatic have evolved gills. Terrestrial have specialised internal structures
How does growth occur in the arthropods?
By ecdysis, have to shed outer cuticle and grow a new one, that is bigger, which they can grow into
How does ecdysis happen?
Epidermis secretes proenzymes which is a moulting fluid, and begins to form a new cuticle. The endocuticle is digested and the cuticle can be shed - exoxcuticle is extra hardened so isn’t digested. New cuticle is safe, and growth happens rapidly before it hardens
What is the largest land crab?
Coconut crab, 50cm
What is the largest aquatic crab?
Giant spider crab, 50cm
What sub-phylums can be seen in the arthropods?
Crustacea, Myriapoda Chelicerata Trilobata Hexapoda
What are the trilobites?
Originated around 500mya, were common in Paleozoic seas. Went extinct in the Permian, 250mya.
What are the three body regions of the trilobites?
Cephalon, Thorax and pygidium
What are the main characteristics of the trilobites?
Had a pair of antenna
compound eye
Biramous limbs
Gnathostome for feeding
Describe the compound eye
Structure give a wide range of vision, made up of ommatidia, which are tiny photoreceptor units, lens leads down to pigment cells.
What classes are found in the chelicerates?
Merostoma
Arachnida
Pycnogonida
What features are shared by the chelicerates?
Have two tagmata, the cephalothorax (so no distinct head) and the abdomen, or prosoma and opithosoma 6 pairs of appendages, uniramous Chelicerae Pedipalps No antennae
What are chelicerae?
A pair of appendages in front of the mouth in arachnids and some other arthropods, usually modified as pincer-like claws
What are pedipalps?
Each of the second pair of appendages attached to the cephalothorax of most arachnids. They are variously specialized as pincers in scorpions, sensory organs in spiders, and locomotory organs in horseshoe crabs
What are biramous limbs?
Each limb has two branches
What are uniramous limbs?
Single branch on each limb
What are the eurypterids and when did they exist?
Water scorpions, existed 400mya, outlasted the trilobite, living until 250mya
What are the features of the eurypterids?
Prosoma made up of cephalothorax, with 6 appendages Compound and simple eyes Telson Chelicerae modified as fangs or claws Lack antennae Mostly marine
What is the telson?
Last segment in the abdomen
In what class and family would you find the horseshoe crabs?
Merostamata, limulidae
Describe the horse shoe crabs
the only marine cheliceriforms left, four living species and are considered living fossils. Chelicerae are reduced, have a long telson
What is special about the blood of horseshoe crabs?
Blood is blue, is removed for medical purposes. Has amebocytes which act as white blood cells
What is the carapace?
Hard upper shell
What species do you find in the arachnids?
Spiders, ticks, mites and scorpions
What are the features of the scorpions?
Earliest group of arachnids
Chelicera reduced
Large pedipalps, as claws, also used in mating
Internal fertilisation by a a spermatophore
Give birth to live young, display parental care
Neurotoxin in stinging apparatus
Book lungs
What are the main features of the spiders?
Reduced chelicera, used as fangs
Spin webs
Narrow pedicle
8 walking legs
How do spiders spin webs?
Using spinnerets, spin silk, which is made of a liquid protein called fibroin, which then solidifies
What are webs used for?
How do spiders digest their food?
Webs, ballooning, food wrapping, protecting eggs - consistency of silk varies with purpose
How do spiders digest their food?
Chelicerae pierce prey, secrete digestive juices onto the prey, so digestion is external. Spider then sucks up the liquid meal
Which spider is vegetarian?
Bagheera kiplingi, feeds on plant material, Benson bodies, on acacia trees. The Benson bodied are protected by ants so spiders have to avoid them
What is a stablimentum?
Structure on a spider web, purpose is unsure, may provide stability, or to prevent birds flying into the web, or even to attract prey or a mate
What benefit is gained from female spider sometimes eating males after copulation?
Nutritional advantage for the female - may be beneficial for males as female gets the extra nutrition. Males make the sacrifice to ensure their genes get passed on.
What is seen in the Nephilia?
Orb web spiders, see huge sexual dimorphism in the sizes of males and female, females are much larger. May be beneficial as can produce more eggs
What are mites? Give an example
Free living and parasitic
Ear mites in cats, or dust mites, or varroa on bees
What are tickets, how do they feed?
Are ectoparasites, feed by filling up their abdomen with blood. Are dangerous as can transmit diseases
Two tagmata may be fused together
What are the pychogonids and what are their general characteristics?
Sea spiders, not true spiders - 1300sp
Most of body is made up of the prosoma
No respiratory devices
Reproductive structures held outside the body
Males carry eggs till they hatch
Mostly small, but grow large in the arctic
