Tardigrada and Onychophora Lecture 14

Question 1

Panarthropods

Answer 1

Tardigrades, Onychophora and Arthropods

Question 2

characteristics of Panarthropods

Answer 2

1. Segmentation (superficial in Tarigrades)
2. appendages with claws and paired segmental legs
3. haemocoel (body cavity with organs and haemolymph)
4. saccate nephridia (sac shaped kidney organs)
5. Molting of chitin exoskeleton
6. tubular dorsal heart in pericardial sinus
7. coelom reduced to end sacs and gonocoel (gonads)

Question 3

Tardigrades and Nematodes

Answer 3

muscular pumping pharynx (stylets, used to suck out plant material)
eutely (growth in cell size, not number)- fixed cell number

Question 4

Tardigrades

Answer 4

terrestrial, fw and some marine spp
body- 4 segments (head +4) with paired limbs with distinct claws
soft cuticle, with soft paddle-like unjointed limbs called lobopods

Question 5

Tardigrade lifecycle

Answer 5

molt 4-6 times total
aquatic or semi-aquatic
thin chitin cuticle

Question 6

Tarigrade molting

Answer 6

exoskeleton, including cuticluar claws, stylets and lining of the fore and hind guts is shed

Question 7

Tardigrade body plan

Answer 7

indefinite segmentation (4 segments and head)
8 limbs, hollow extensions of body wall (clawed legs)

Question 8

Cryptobiosis in Tardigrades

Answer 8

shared with nematodes
Anhydrobiosis (periods of desiccation)- shriveled appearance
- recovery after immersion in liquid helium, alcohol, brine and ether

Question 9

Anhydrobiosis

Answer 9

trehalose (sugar) moves into cells to replace lost water and tardigrade curls into small shriveled ball (tun)
metabolism lowers to 0.01% of normal

Question 10

Advantages of clinging to plant structures

Answer 10

prevents being carried away by floods
protects, less covered ventral side
process of desiccation has time to proceed in optimal manner

Question 11

similarities of Tardigrades and Onychophorans

Answer 11

unjointed appendages that end in claws

tardigrades lack: antennae, jaws and respiratory system

Question 12

Onychophorans

Answer 12

terrestrial predators of insects
soft cuticle, lack exoskeleton
paired, unjointed limbs (lobopods)

Question 13

Onychophoran cuticle

Answer 13

-hydrophobic skin
arthropod like exoskeleton, but unsclerotized
cuticle contains a-chitin and protein
non-articulated, covered in hundreds of papillae and sensory hairs

Question 14

three pairs of head appendages

Answer 14

antennae
mandibles
oral papillae

Question 15

head segments

Answer 15

two large antennae with eyes at base
jaw-like mouth
holds first pair of lobopods

Question 16

unique trait of Onycophorans

Answer 16

slime papillae used to ensnare prey

able to re-use slime

Question 17

Fossil evidence of Onycophorans

Answer 17

marine dwelling- Hallucigenia

tube-legs and spines on back (related to Hallucigenia)

Question 18

Diania

Answer 18

fossilized lobopodian
most robust and arthropod-like limbs
- derived position close to Arthropods
acquired key evolutionary innovation: sclerotized, jointed appendages began to fully develop
- sister taxa to arthropods based on apomorphy of jointed trunk appendages

Question 19

Diana evolutionarily important because

Answer 19

suggests arthropodization (sclerotization of limbs) preceded arthrodization (sclerotization of body)