Chelicerates Flashcards
Name some Chelicerates
Spiders, scorpions, ticks
What are the main features of a chelicerate central nervous system?
Concentrated in the prosoma Ventral nerve cord with ganglia (largest = brain) Large optic lobes of brain Oesophagus goes through the brain Highly cephalised nervous system
Discuss chelicerate eyes
They are ocelli (simple eyes)
Most spiders have 8 eyes in 4 pairs. The main eyes are direct, the rest are indirect with a tapetum, which improves light capture. Spiders have the best chelicerate vision, it is even possible that jumping spiders have tetrachromic vision, they can also point their eyes in different directions
What are pectines?
Sense organs unique to scorpions. They swing back and forth when walking and bear mechano/chemoreceptors
Describe a chelicerates circulatory system
Tubular heart with ostia and aorta
Heart lies within a pericardium which is linked to the book lung
In spiders, blood pressure is responsible for extending the legs
Describe a chelicerates respiratory system
It is less extensive than insects
Just a couple of tubular tracheae and a single spiracle
What is a book lung? And what are the names given to arachnids with and without one
Internal series of lamellae with a rich blood supply. It acts as the surface area for gas exchange
Pulmonate and Apulmonate
What is the difference between Araeneomorph and Myaglomorph spiders?
Araeneomorph spiders fangs move sidewards like a pair of scissors. Myaglomorph spiders fangs move forward and backwards, they also have two pairs of book lungs.
What are the two main properties of spider and scorpion venom?
Neurotoxic peptides and proteins
Necrotising
Describe a chelicerates digestive system
They ingest already liquidized food that has been smothered in protealytic enzymes. Their sucking stomachs draw food in and their large gut capacity and low metabolic rate means then can go for long periods without feeding. Nitrogenous waste is precipitated out and stored in a stercoral pocket, where it is mixed with faeces
Describe a chelicerates reproductive system
They have gonads, and most chelicerates lay eggs.
Name four ways spides locomote
Legs
Silk
Cartwheeling
Phoresy (hitching a ride!)
Name four ways chelicerates capture prey
Active searching
Ambush
Active searching and ambush
Interception
Discuss spiders courtship and mating behaviours
Olfaction and gustation are used to locate females ready to mate
Females place pheremones on their webs to signal readiness to mate
Before mating, male spiders prepare by placing a drop of seminal fluid into their pedipalps via capillary action, which he then transfers to the females epigyne
Many spider species participate in sexual cannibalism!
To avoid being eaten post-copulation, male spiders will;
Sting/bite female before mating to immobilise, or restrain with silk
Preferentially mate with a newly moulted female
Bring a diversionary meal
