Hard Wrackline Objects

Shipworm Whelk Eggcases Skate Eggcase

What are they?

The wrackline or strandline consists of a line of objects washed up on the beach and left stranded when the tide retreats. Walking the line can be a fun way to find all manner of saltwater, aquatic wildlife - or signs of such things. Although much of the line is likely to be made up of pieces of dead plant material and other detritus, other objects will soon be found with careful searching. This page helps with the identification of hard-surfaced objects that might be found on the beach. This often includes the hard remains of creatures that in life may actually be soft-textured, as well as objects such as pieces of wood that shows signs of damage from boring creatures. The shells of coastal shellfish and crabs are covered in a separate section and can be searched for by clicking here


Hard wrackline objects usually survive stranding on the beach better than soft-bodied objects. However, it should be remembered that some hard objects may be the partial remains of larger creatures, from which the softer parts have disappeared. Some objects are a mix of hard and soft, so you will find them included on the pages for both hard and soft objects.

  Shipworm     Teredinidae

Though rather worm-like in appearance, shipworms are actually bivalve mollusks and have a small shell at the front end of the body. Your are unlikely to find stranded shipworms, but you will find evidence of them in washed up pieces of wood. Look for neatly rounded holes in the wood, leading to smooth-sided tunnels. Shipworms have serrated edges to their small shells, which are used in the drilling process; they can be a problem in any untreated wood that spends time submerged in saltwater, such as wooden pilings and boat hulls. Our commonest species is the Common Shipworm Teredo navalis
Shipworm Shipworm

  Whelk Eggcase     Gastropoda

The egg cases of the larger whelks (also known as conches) are a common sight on our beaches. They usually wash up after the eggs have hatched, but remain attached to each other in long strings. Look for the holes where the youngster emerged (photos courtesy of Megan Crewe).
Whelk Eggcases Whelk Eggcases

  Skate Eggcase     Chondrichthyes

The egg cases (often called mermaid's purses) of several species of skate may be found washed up on the beach, but telling the different species apart can be difficult. Skate are flatfish that are related to sharks and many species of both groups produce egg cases. Eggs are laid in small 'envelopes' which have tendril-like corners that help the case to attach to seaweed on the sea floor. After eggs have hatched, the leathery, empty cases eventually break loose and often get washed up on the beach.
Skate Eggcase