Chelicerata- Subgroup of Mandibulata Flashcards
What are the major groups of Chelicerates ?
Sea spiders and the Euchelicerata
Give the 2 main body units of this group
PROSOMA
OPISTHOSOMA
May appear undivided (internal segmentation) or separate (external segmentation)
Give the number of embryonic segments of each main body unit
Prosoma-6
Opisthosoma- 12
Where is the post anal telson found ?
On the Opisthosoma, it is not considered a true segment
What is found on the Prosoma ?
Chelicerae-feeding appendages Pincers 1 pair of pedipalps 4 pairs of walking legs NO antennae or true mandibles
What has happened to a spiders pincers ?
They have modified into fangs
What is found on the Opisthosoma ?
Respiratory structures (lungs/gills) As well as Spinnerets- spiders
Describe the importance of a pycnogonids limbs ?
4 pairs of long limbs, (hollow)
Organs extend into limbs
i.e Digestive system
What are Pycogonids ?
Sea Spiders
Sea spiders can be commensal feeders, what does this mean ?
They benefit off an organism without impacting them in any way.
Describe the feeding strategies of Sea spiders.
Can be ECTOPARASITES (outside of host) of invertebrates
Or Commensal Feeders
Describe key adaptions of the horseshoe crab.
Large carapace, to the protect Prosoma
Long telson, to flip themselves upright
Gnathobase, grinds up food before transferring it to the mouth
3 walking legs with and without claws, for movement and protection
How does the horseshoe crab see ?
By compound eyes found on the dorsal carapace.
What were the Eurypterids ?
Water scorpions, now extinct
Could grow very large (human)
Mesosoma and metasoma body segments
Enlarged chelicerae
Where are scorpions found ?
In tropical environments
Arid, humid, warm environments
Give the key adaptions of scorpions.
Telson, with highly venomous glands for defence and predation
Hugely modified pedipalps
What is the most successful and diverse group of chelicerates ?
Spiders
Do spiders have visible external segmentation ?
NO
What is the Pedicoel ?
A connection between the prosoma and the opisthosoma
What is different about the chelicerae of spiders ?
Modified into fangs and venom glands
Plesiomorphic fangs…..
Primitive, Fangs point forwards
Apomorphic fangs….
Derived, Fangs point vertically
When spiders die, why do their limbs curl into their body ?
When alive, the pumping stomach provides pressure to extend the limbs. Muscles will then contract the limbs inwards.
These muscles remain contracted upon death, therefore the limbs will curl up.
What is a book lung ?
A more advanced respiratory structure than a book gill.
Highly folded area, internalised
Haemocoel & haemoglobin as resp. pigment
Can switch between pigments
Found in Arachnids
Which species have a book Gill?
Horseshoe crabs??
What is a spinneret ?
A group of modified appendages, which produce silk.
Describe the process of silk production in a spider
Silk is extracted in liquid form from the spigot.
As the spider pulls the silk, it polymerises the proteins from liquid into a solid.
Adjacent spinnerets secrete an oily substance to line the silk.
Give some of the purposes of silk
Wrapping eggs Wrapping Prey Drag line silk Spiral line silk Web Frame
Give other methods of catching prey, rather than casting webs
Dig a burrow which is lined with silk.
Lasso the prey with silk.
Camouflage is crucial for these methods of prey capture.
How many eyes do spiders have ?
Usually 8 eyes in 4 pairs
2 types of eyes.
Main eyes…..
Secondary eyes….
Give wide view
Peripheral view, movement detection.
Give an adaption of the secondary eyes.
They have a reflective tapedum, which enables vision In low light.
Why are pseduoscorpions not real scorpions ?
They have an elaborate pedipalps but no stinging telson.
Give an adaption of the Vinagaroon.
Injects vinegar to deter predators
Give the common name of Opiliones.
Daddy long legs
Have no silk or toxins.
