The occasional weathered and empty common whelk shell are also present amongst the seaweed. Most are broken to some degree, making the intricate internal structure visible. This one was intact. These whelks are carnivorous, feeding on marine worms and other molluscs such as bivalves (which have two halves to their shell). Whelks can use the edge of their own shell to prize open bivalve shells to feed on them. Common whelks also feed on dead animals, which they locate by smell using their siphon. They wave the siphon back and forth to detect where the smell of food is coming from. Empty shells such as this one are sometimes used as a temporary home by hermit crabs as these crabs have no protective shell on their abdomen.
These dark coloured egg cases belong to rays, a relative of sharks. In contrast to the whelk eggs, these egg cases contain a single embryo. The capsules hatch after 5 or more months (depending on the species). Several UK species of ray have greatly declined over the last few decades. The Shark Trust are collecting records of ray egg cases on the beach to help locate nursery grounds to better protect UK species so they have a chance to recover. If you find a ray egg case the records should be sent to the Shark Trust, http://www.eggcase.org/
A couple of years ago I worked with Brighton based River Ocean Foundation as Education Coordinator for a project called Ocean 2. As part of this project I worked on a strandline exhibition that was set up at the Booth Museum of Natural History also in Brighton. The exhibition was made up of various displays that focused around the seashore strandline. These included a replica beach, the forces that created the strandline, scavengers, myths and folklore, beach object identification, amazing eggs, marine litter, stranded sea mammals and more. When the exhibition came to an end, River Ocean Foundation created a website including images of the exhibits and all the original text I wrote for the exhibition.
To find out more about the strandline you can visit the website at http://www.riverocean.org.uk/ocean/exhibition/digibooth/Strandlinehome.htm