ECDYOSZOA Flashcards
Key Ecdyosozan traits
- a cuticle made of chitin, and growth by moulting (ecdysis).
- No external cilia and loss of ciliated larval forms.
- Coelomic spaces are largely replaced by a haemocoel.
What proved Ecdysozoa to be very very distant from annelids?
DNA sequence and developmental data show the Ecdysozoa to be derived from a shared common ancestor
8 phlya in Ecydoszoa
- Priapulida (praipulid worms)
- Kinnorhyncha (kinorhynchs)
- Tardigrada (Tardigrades/ water bears)
- Nematomorphs (horsehair worms)
- Onychophora (Velvet worms)
- Arthropoda
- Loricifera (loriciferans)
- Nematoda (nematode worms)
Phylum Onychophora (velvet worms)
Predators of other invertebrates in tropical forests
in the southern hemisphere.
- Seen in the past as a
link between Arthropods and Annelids?
Phylum Tardigrada
- Very small, found in all aquatic habitats.
- Body composed of head plus 4 limb-bearing ʻpseudo segments.
- Feed using a pointed, hollow stylet.
- Cell number fixed at birth (eutely); grow by cell enlargement not division.
Phylum Nematoda
- thread like worms
- also EUTELIC and feed with STYLET
- many are parasitic and show complex lifestyles
How do onychophorans show original ceolomate structure?
What have arthropoda and nematoda developed instead?
Nephridia carry out excretory functions
2) - Insects and nematodes have lost the original nephridia, and have independently evolved new systems.
- In nematodes, the new system is part of the epidermis
(ectodermal renette cells). - In insects it is derived instead from the gut (endodermal Malpighian tubules)
a) Is anyone segmented?
b) What do the segmented phyla lack?
- Arthropods are segmented (tardigrades and Kinorhynchs show segment-like development) - similar to Annelids, but without coelomic spaces and septa.
- Other groups (such as nematodes) show no sign of segmentation.
Describe cuticle structure
- Made of Chitin, a polymer of N-acetyl glucosamine
that is structurally similar to cellulose, which forms a matric of fibres whose properties can be altered by adding minerals
-
What can be added to the cuticle?
PROTEIN FIBRES for hardness and elasticity
WAXES for waterproofing
Why are nematodes so different?
- Excretory system unlike anything in other groups.
- Only have longitudinal muscles.
- No sign of circulatory or gas exchange structures
CRYPTOBIOSIS (physiological state in which metabolic activity is reduced to undetectable level without disappearing)
1) Why ?
2) How ?
3) Who ?
1) - Allows wind dispersal across inhospitable habitats
- Allows exploitation of temporary habitats by aquatic species (nematodes, tardigrades)
-For parasites, cryptobiosis allows:
• persistence in areas where hosts are rare, and
• passive transmission under unfavourable conditions
2) - exposure of thin cuticle is minimised
- also waterproofed
- metabolic rate greatly reduced
- body accumulates compounds to protect against tissue damage, resist crystal formation
3) Tardigrade adults
Nematode larvae in flesh of intermediate host
Why are nematode species so abundant despite - heamocoel structure limiting overall structural diversity?
BUT there is enormous physiological diversity, in particular in traits allowing survival on or in specific plant and animal hosts.
• As hosts diverge, so their specific parasitic nematodes have radiated with them (Fahrenholzʼs Rule).
How do nematodes locomote?
Fine structure of cuticle (running 54’ to long body axis) and high internal pressure is crucial, to be manipulated by the longitudinal muscles.
3 phyla of unsegmented worms in this lineage
- Nematoda
- Nematomorphs
- Priapulida
