A Closer Look at Arthropod Features Flashcards
What is the exoskeleton of arthropods made up of?
Chitin
How do increases in body size occur in arthropods?
Through ecdysis (moulting), occurs periodically when the exoskeleton is shed in a stepwise pattern
What are periods between moults of exoskeleton called?
Instars
What are the two parts of the procuticle of the exoskeleton?
Endocuticle and exocuticle
What part of the exoskeleton is re-absorbed at moulting?
Endocuticle
What is the exocuticle strengthened by?
Biomineralisation and cross-linking of proteins
Where do arthropods not have exoskeleton and why?
At the joints as these need to be flexible
What is the outer section of the exoskeleton called?
The epicuticle
What is a key characteristic of the outer epicuticle in terrestrial athropods?
Waxy epicuticle
Explain the moulting process - ecdysis
- Intermoult stage - the epidermis starts to separate from the old cuticle
- Apolysis - epidermis separates from the old cuticle
- A new epicuticle is secreted from the epidermis to protect it from digestive enzymes
- Fluid is secreted from the epidermis to fill the space between the two layers
- Epidermal cells divide to prepare for increase in size
- New cuticle is secreted by the epidermal cells
- Enzymes in the moulting fluid are activated and reabsorb the endocuticle
- The old exocuticle splits due to fluid pressure
- Animal sheds old cuticle and new starts to harden
Are crustaceans all free-living?
Majority are free-living, but many sessile, commensal and parasitic species
What is a paraphyletic group?
A group that includes a single common ancestor, and only some of its descendent lineages
What is a monophyletic group?
A group that consists of a single common ancestor and all of its descendent lineages.
What is a polyphyletic group?
A group that has shared characteristics that have evolved in different lineages and do not have a common ancestor.
What is included in Pancrustacea?
Crustacea and Hexapoda
Is Crustacea a monophyletic, paraphyletic or polyphyletic group?
Paraphyletic
Is Pancrustacea a monophyletic, paraphyletic or polyphyletic group?
Monophyletic
What are the definitive features of the external morphology of crustaceans?
- Fused head and thorax
- Elongated abdomen (referred to as carapace)
- Long antenna to sense differences in chemicals in vast body of water
- Range of walking limbs
- Biramous limbs (2 parts) - mouthparts are also modified limbs
- Mouth situated underneath body
What is special about the leg morphology of crustaceans?
Show remarkable specialisation for a range of tasks.
How is there a high diversity of crustaceans successful in different environments?
Due to modified, biramous limbs
What kind of legs did ancestral arthropods likely have?
Biramous legs with limited specialisation, although uniramous legs thought to gave evolved multiple times
What is leg development controlled by?
Hox-genes
Describe the internal morphology of crustaceans.
- Range of glands at front of mouth to detect chemicals in water, such as for prey or mating
- Antennal gland linked closely with the bladder
- Large stomach behing head
- Malphigian tubules allow waste to be excreted while retaining water and salt in haemolymph
- Have internal gills - water taken up between jointer regions of gills and pushed over mouth using modified appendanges
- Similar to book lungs
- Store water within their exoskeleton, meaning can breathe on land
What are the evolutionary trends within crustaceans?
- Specialisation of biramous limbs
- Shortening of body, linking with development of the carapace - means more robust and less susceptible to damage (hardened carapace beneficial for water current)
- Development of the carapace
- Calcification and pigmentation - for hiding in marine environment or to display certain characteristics (e.g. defence)
