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