The Flintback Drifter

All in one day, amazing, walking along the Brighton pebbles, I found four different varieties of the Flintback Drifter. Unusual to see at the best of times, but four was like winning the lottery. There must have been a storm in the Channel, or some such peculiar weather system to have caused such a windfall of marine rarities.

The Flintback Drifter is a little-understood marine species that perfectly mimics flint stones, lying motionless among the pebbles of tidal zones. It is believed to be an evolutionary marvel, capable of remaining more or less inert for decades before gradually shifting into a more animate state. For those new to the species, here is a fact file.

Scientific Classification
Kingdom: Animalia
Phylum: Chordata (disputed)
Class: Lithopoda (proposed)
Order: Cryptosiluriformes
Family: Silicamariidae
Genus: Silicamaris

Species (numbered as in photos)
1) Silicamaris dormiens (Dormant Flintback Drifter)
2) Silicamaris lithomimus (Stone-Mimic Flintback Drifter)
3) Silicamaris vivens (Living Flintback Drifter)
4) Silicamaris mutabilis (Transitional Flintback Drifter)

Size: 20–50 cm (depending on life stage).
Color: Varies from deep grey to mottled black and white, mimicking natural flint and beach pebbles.
Texture: Hard, rock-like exoskin with occasional glossy fractures resembling chipped stone.
Body Structure: Appears almost featureless at rest but reveals faint ridges, a ventral mouth slit, and sensory pits when active.
Habitat & Distribution: Found exclusively along shingle beaches, particularly in Sussex, UK. Prefers intertidal zones, where it can remain still among pebbles, rarely moving except at night or during storms. Some reports suggest it may also drift along deeper seabeds, using its flint-like exterior to deter predators.
Feeding: Although widely thought to be pebble-eaters, they are slow-moving filter feeders, absorbing nutrients through microscopic pores when submerged. Some speculate it may consume small marine organisms using a concealed underbelly mouth.
Movement: Almost imperceptible. Shifts position by subtle expansions and contractions of its dense, flint-like tissue.
Defense Mechanism: Extreme camouflage. When disturbed, it remains motionless, indistinguishable from real stones.
Life Cycle & Evolution: Begins as Silicamaris dormiens, indistinguishable from a common flint stone. Over time, it may transition into Silicamaris lithomimus, showing faint organic features. Eventually, it develops primitive limb-like ridges and becomes either Silicamaris mutabilis or Silicamaris vivens (though marine biologists dispute whether these are two distinct species). Flintback Drifters may live for hundreds of years, growing at a nearly imperceptible rate, though much about these creatures remains unknown.