Having briefly worked in the Natural History Museum in London, i had the pleasure of listening to a lecture by Richard Fortey who is known for a whole list of popular science books. One of these books, as ibrecently found out has nearly a whole chapter set in Hong Kong and dealing with some of Hong Kong’s lesser known marine animals.
In “Survivors: the Animals and Plants That Time Has Left Behind”, Richard Fortey visits East Sai Kung Country Park with Professor Paul Shin of City University, to explore some mudflats looking for creatures that are rare survivors of past geological ages millions of years ago.
You may be familiar with this animal:
The coelacanth is a lobe-finned fish thought to be the ancestor of all land vertebrates. Having evolved 400 million years ago, it was thought extinct for 66 million years until famously it was discovered living in 1938. That made it the poster boy for living fossils. But few Hongkongers would suspect a living fossil in their city, let alone 4!!!
One of these is Lingula anatina. It consists of two valves forming a clasped shell and a long stalk or pedicle. The pedicle is buried vertically in the sediment to anchor the animal while its valves open to filter tiny edible pieces out of the sea water at the sediment surface.
To an untrained eye this might seem like mussel or clam or other mollusc. But it is in fact a brachiopod, a group of animals that has been around for about 500 million years. To put that into context, the colonisation of land by plants happened 400 million years ago. How a brachiopod differs from a mussel or clam is its internal organs and body structure – but that’s a matter for undergraduate invertebrate textbooks….
Lingula for all its similarity to a mussel, is not a mollusc, but the next living fossil is. The chiton Acanthopleura japonica is very ancient and primitive mollusc.
The animal is similar to a snail but instead of a shell it has 8 armoured plates which it locks together to form a shield. They use a muscular foot to glide around rocks scraping algae off them. If scared or at low tide they suck themselves onto the rock with their foot and at the same time lift their shell to form a vacuum – so prying them off rocks is not recommended as you will only end up breaking and killing them. If they do get pried off rocks they roll up a bit like a wood louse. Acanthopleura is a common sight around Hong Kong’s rocky shores. And chitons very similar to it started appearing about 450 million years ago…for context, dinosaurs appeared about 200 million years later…and in all that time they really haven’t changed much.
The third living fossil is a type of worm. The Peanut-worm to be precise, so named because it can bunch itself into a peanut-shaped blob. Its proper name is sipunculid worms, and they too have been around for almost 500 million years. As with brachiopod sand mussels, the difference between a sipunculid and a ‘regular’ marine worm is in its internal body structure and organs. Hong Kong actually hosts at least two species of sipunculid worm. One of these is Siphonosoma cumanenses, pictured below. It makes burrows on fine sandy shores.
The other is Sipunculus nudus, pictured below, which is – not surprisingly – also eaten in Southern China.
Finally, there are the horseshoe crabs, but that is for Part 2…