ECHINODERMATA Flashcards
Deuterostomes
Mouth forms from outpockets of the gut
Classes (6)
Charlie And Ella Only Have Cuddles
Crinoidea (sea lilies and feather stars)
Echinoidea (sea urchins and sand dollars)
Asteroidea (starfish)
Ophiuroidea (brittle stars)
Holothuroidea (sea cucumbers)
Concentricycloidea (sea daisies)
Key characters
- Deuterostome
- Pentaradial symmetry with ancestrally upward facing arms
- catch connective tissue
- endoskeleton calcium carbonate
- have bilateral symmetrical larvae
- internal anatomy dominated by fluid filled coelomic spaces, particularly the water vascular system (WVS)
- diffuse nervous system with no brain
Echinoderm skeleton
- Mineralised internal skeleton
- Catch-connective tissue
- Hydrostatic skeleton
The skeleton is a lattice of calcium carbonate, called the stereom, surrounded by living tissues. Elements are fused to form rigid Tests.
Living surfaces often tipped with what?
Poison glands and defensive pedicellariae
a) What is catch connective tissue? What is so good about it?
b) How is it stimulated?
c) How do echinoderms therefore move?
a) Extracellular matrix of collagen fibres that are supplied by a meshwork of neurosecretory cells.
b) Nerve impulses and then calcium ions that cause cross link formation and ‘lock’ tissue into place.
c) By an active process to unlock the tissue via muscle contraction.
Ancestral state of WVS? How about most species now?
Facing upwards now downwards
What is the WVS connected to and used for ?
Connected to tube feet through radial and lateral canals .
Above each foot is a fluid reservoir called the ampulla. Valves allow each ampulla to work independently.
Muscle contraction is used to force water into the tube feet and out again in order to take steps.
USES: The WVS operates the tube feet that most echinoderms use for one or more of feeding, locomotion and gas exchange
What do the Crinoids (feather stars) and Ophiuroids (brittle stars) use for locomotion?
NOT TUBE FEET
Muscles in arms
How do Crinoids feed ? As opposed to tube feet
Both feather and brittle stars aid food capture by positioning themselves across currents
Which species have the most modified tube feet, used in deposit or suspension feeding?
Sea cucumbers.
How are urchin tube feet specialised?
divided internally, and provided with cilia inside and
out , to provide efficient gas exchange
What are papullae?
thin parts of body wall used in efficient gas exchange
What is cephalisation?
Why does this relate to pentaradial symmetry?
the concentration of sense organs, nervous control, etc., at the anterior end of the body, forming a head and brain, both during evolution and in the course of an embryo’s development.
2) This body design lacks and obvious front end,
Echinoderms begin as (a) larvae, and superimpose their (b) symmetry upon its bilateral nature.
a) dipleurula
b) pentaradial
