Clade Ecdysozoa features? What is their shared, derived trait?
- monophyletic
- 2 major phyla: nematoda, arthropoda
cuticle that is periodically moulted - tough outer layer outside epidermis, secreted by epidermal cells
- composed of chitin
What are functions of the cuticle?
- barrier against dessication and mechanical injury
- structural support; tough exoskeleton that acts as a framework for muscle attachment
- must be shed through ecdysis for animal to grow
3 layers of the cuticle?
Endocuticle + exocuticle (procuticle)
epicuticle - thin waxy
fine ducts run from the epidermis to the top of the cuticle
What is ecdysis and its function in arthropods?
Moulting
- cuticle is sclerotized forming a hard, rigid cuticle
- regions of sclerotized cuticle shaped like plates are called sclerites
- used as armour plates and hardened appendages
How does ecdysis work?
1) Ecdysozoan becomes inactive and apolysis separates old cuticle from epidermis
2) Inactive enzymatic moulting fluid is secreted into sepration spce and epidermis grows in a folded manner
3) A new proto-epicuticle is secreted on the epidermis
4) Moulting fuid enzyes are activated and old endocuticle is digested but sclerotized exocuticle isnt
5) New procuticle layer is secreten protecting proto-epicuticle from digestion
6) Moulting fluid is reabsorbed and deposition of new epicuticle is complete
7) Old exocuticle is moulted and new cuticle expands
Phylum Nematoda characteristics?
- aquatic roundworms without segmentation, eyes or appendages (lost secondarily)
- anterior blunt, posterior pointed
- hemocoel lined with mesodermally-derived tissues but not completely
- movement by side-side contractions of longitudinal muscles
- sexual reproduction, internal fertilization, direct development
Phylum Arthropoda evolution is characterized by?
- decreased number of body segments
- increased appendage specialization
- Hox gene sequence regulation
6 characteristics of arthropods?
Segmented body
Jointed paired appendages
Sclerotized cuticle
Cephalization
Reduced coelom
Open circulatory system
Body segments and limbs are arranged into?
Tagmata
What do arthropods have in the head region?
feeding structures and sensory structures
eyes, antenna, olfactory receptors
Why do they have a reduced coelom?
Strong, segmented limbs reduce need for hydrostatic skeleton
Hemocoel supports internal organs
What does the hemolymph do?
circulates in hemocoel surrounding tissues and organs
may have respiratory pigments for oxygen transport
What are the 3 lineages of arthropods?
Subphylum Chelicerata, Clade Pancrustaceans, Subphylum Myriapoda
Features of subphylum Trilobita?
- extinct marine arthropods
- 3 tagmata: cephalon, thorax, pygidium (tail)
- compound eyes, flexible antenna
- thoracic segments had one pair of biramous limbs (ventral - locomotion, dorsal - gill)
Which feature of trilobites did arthropods lose?
Lost dorsal branch of limbs so their limbs are uniramous
Subphylum chelicerata features? (specifically chelicerae)
- claw-like feeding appendages called chelicerae
- mouthparts adapted for feeding and defense
- homologous to antenna
- 2 or 3 segmented pincers
- chelicerae in spiders have venom glands
- spiders, scorpions, mites
- 2 tagmata
What are the 2 tagmata of Chelicerata?
Anterior cephalothorax - covered by carapce; dorsal exoskeleton
- 6 pairs of appendages: chelicerae, pedipalps, 4 pairs of legs
- pedipalps are jointed sensory appendages
- no antennae, uniramous limbs
Posterior abdomen - no appendages; contains digestive and reproductive organs
Arachnid features?
- fluid-feeding predators
- eye spots called ocelli
- abdomen and cephalothorax with 6 pairs of appendages
- separate sexes
Spider features?
- 2-segment chelicerae with venom glands
- gas exchange via book lungs in abdomen
- 0-4 pairs of ocelli
- spinnerets - abdominal glands producing liquid protein silk
- maternal care of eggs and sometimes young
- complex courtship
Scorpion features?
- pedipalps modified as pincers
- segmented abdomen
- terminates in poisonous stinger
- digest externally and ingest fluid
- complex courtship
- maternal care of eggs and young
Mite features?
- no segmentation between cephalothorax and abdomen
- 2-3-segmented chelicerae
- 0-2 pairs of ocelli
Subphylum Myriapoda characteristics?
- terrestrial and less tagmatization
- simple eyes, 3 pairs of mouthparts (1 mandibles), one pair of antennae
- over 3 pairs of jointed uniramous legs
- gas exchange via tracheal system; air enters lateral spiracles, through trachea, into tracheoles throughout the body
- lack O2 trasporting pigments in hemolymph
- direct development
2 types of myriapods?
Millipedes - detritivores or herbivores with 2 pairs of jointed legs/segment
- diplosegments due to fusion of adjacent segments
Centipedes - predators with 1 pair of jointed legs/segment
- venomous claws
What does Clade Pancrustaceans include?
Subphylums Crustacea and Hexapoda
