I laid what seems to be the skeletonised limb of a very large starfish out on a nearby patch of sand, to make a cursory analysis. It appears to be a thread starfish, of a type unknown to me.
Field sketch of the starfish
Measurements:-
51cm in length
Tapers in width from 15cm to 3cm
Appearance:-
The tip is a circle with a 16mm looped border
Progressively wider semi-circles along the length, with a 16mm looped border increasing to 23mm
The skeleton appears to be made from a fine coarse white fibre
Further analysis of the thread and structure will need to be carried out in the lab.
