17 December 2008

Pool of Suprises at Pasir Ris

What can you see in a pool of seaweeds and seagrasses?A whole galaxy of tiny creatures!

I spent a long time at this small, seemingly trashy pool on the high shore at Pasir Ris towards the end of the low tide. And was astounded by the variety and number of tiny, busy creatures that I saw!There were countless tiny little swimming crabs that will grow up to be Flower crabs (Portunus pelagicus). They came in all kinds of colours and patterns, as well as sizes.There were also minute spider crabs that looked like bits of fluff, and tiny hermit crabs each in a tiny shell.There were tiny snails of all kinds. And tiny shrimps.And lots of tiny little gobies.
There was this strange worm-like animal that lived inside some sort of thick casing. It jerked around dragging the casing behind it. I have no idea what it is.There was a really REALLY TINY sea urchin. Next to it is a beachflea (Order Amphipoda).
The pool was packed with animals! The blob at the top is a bubble shell snail (Family Hamineoidae). There's the obvious pipefish with a tiny crab hitching a ride on it. At the fish's nose is a tiny wooly leaf slug. And next to the slug seems to be an egg mass laid in a coil.There were a lot of pipefishes there. Some were really thin and tiny. We've seen these also at Changi and other northern shores.
There were a lot of wooly leaf slugs too! It's easy to overlook them as they look like mere bits of fluff. Here's a closer look at one. These are sap-sucking slugs (Suborder Sacoglossa) and are not nudibranchs. They have a pair of tentacles made up of rolled tubes, and a pair of flaps.This is the Cerberilla nudibranch (Cerberilla sp.) and there were several of these pretty animals in the pool. The yellow colour in the finger-like projections on the body is actually in the digestive glands. The rhinophores at the top of the head are very short compared to the long oral tentacles (the long tentacles that stick out on the sides like a moustache). Young nudibranchs have longer oral tentacles relative to their body size.This was was lying on its back. I have no idea why.
Here's another Cerberilla nudibranch from the pool. The references suggest that these nudibranchs eat sea anemones.

And there sure were lots of tiny sea anemones in the pool!But most of the tiny sea anemones seen were stuck onto the shells of living whelks (Family Nassaridae). This one has two sea anemones, one open (on the right) and one closed (on the left).In fact, most whelks seem to have two sea anemones.But some had three! You can hardly see the shell of this snail. The only bit of the snail that you can see is the tip of its siphon (the tube-like thing that sticks of out the shell).Sometimes, the whelk is buried in the sand and all you can see are its anemones and its siphon (in the photo, the siphon casts a shadow).

Does living on a whelk help the sea anemone avoid being eaten by the nudibranch? I didn't actually see any of the nudibranchs attempt to eat the anemones though. Wow! There sure is a lot to see and learn about our shores.

But photographing tiny creatures is really hard on my back! Ouch!

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