Marine section 3.4: Invertebrates

 The syllabus states:

dentify and describe the main characteristic features used to place marine invertebrates into groups within the animal kingdom .

limited to: 

(a) crustaceans 

bilateral symmetry 

exoskeleton 

compound eyes 

 two pairs of antennae

 abdominal segments with jointed legs 

(b) cnidaria 

radial symmetry 

tentacles with stinging cells 

(c) echinoderms 

pentaradial symmetry 

spiny skin  

tube feet

 (d) molluscs 

bilateral symmetry 

unsegmented body 

internal or external shell

 (e) annelids •

bilateral symmetry 

segmented 

 soft body 

setae  

My notes are here:

The AS marine syllabus also coveres some of those points:

Crustaceans:

Be aware that the syllabus only toutches on some of the marine invertebrates. The Marine sponges, bracciopods and many other interesting animals are not included. 

Its important to know that Cambridge here chooses a few model organisms, that are common and important.