Arthropods and Trilobites Flashcards
What is the age range of phylum Arthropoda?
Cambrian to recent
What % of all animals described are Arthropods?
75%
What ranking debate is there concerning arthropods?
Whether phylum or superphylum
and
If they form a natural (monophyletic) group
What variety if there for arthropods?
Position, number and morphology of their limbs
Where do Arthropods fall on the group tree?
Metazoa, Bilateria, Protosomes, Ecdysozoa
What are phylum arthropoda united by?
Possession of a jointed exoskeleton which is often hard and inflexible
What are the advantages of exoskeletons?
Support for soft tissue
Firm site for muscle insertion
Protection (predators and environment change)
Division of skeleton into jointed sections
What is the advantage of exoskeletons dividing the skeleton into jointed sections?
Will act as a series of levers allowing for precision in locomotion, feeding etc
What are the limitations of exoskeletons?
To grow Ecdysis must occur (moulting) leaving the arthropod vulnerable
What % of arthropod mortality arises from Ecdysis?
70%
What can an exoskeleton allow to happen within a lifecycle?
allows animals to change morphology (metamorphosis)
What is the segmentation of Arthropoda like?
Segments = Metameres
Grouped into Tagmata
What does the grouping of segments into tagmata allow for?
feeding
locomotion
sensory systems
visceral elements (gut carrying)
What is a sister group of arthropods?
Phylum Onychophora (Cambrian - recent)
What is the closest relative to true (eu) arthropods from Onychophora?
Peripatus (recent)
What is a fossil record example of Onychophora?
Hallucigenia (Mid Cambrian), Burgess shale
What is a fossil record example of Chelicerata?
Sanctacaris (Mid Cambrian), Burgess Shale
What are some examples of present day Chelicerata?
Spiders
Mites
Scorpions
What is a group that branches from Chelicerata?
Merostomata
What is the present day and fossil record example of Merostomata?
Xiphosurids (Limulus) - present
Eurypterids - past
What was Eurypterid like in its environment?
In the middle paleozoic shallow water and terrestrial setting it was t