Stalkers of the Blue Fleet. Part 1: Glaucilla marginata

Combing the newly-cast strandline on a storm-battered beach is possibly the most fun a nature fanatic can have on their own. NSW central coast this Christmas was especially good. The storms came one after another all week and I spent many an hour strolling the glistening sands of South West Rock's Main Beach. In past seasons this beach has thrown up many gems, once a magnificent Nautilus came bobbing ashore as I watched, but thats a story for another day.
On the best day of the week for wrecked sealife, I noticed tiny striped splodges mixed with the blue tentacles and wobbly bladders of the abundant Man'O'War jellyfish Physalia phisalis. (OK, OK, in Australia they are called Bluebottles, and they are not actually jellyfish but properly a zooid Siphonophore- happy now?) I happened to have a plastic tub with me (as you do). I filled it with seawater and popped one of the droopy splooges in. On hitting the water it sprung back to life- a shining perfect little nudibranch called Glaucilla marginata. In a flurry of excitement I took dozens of photos. These are special molluscs indeed- ruthless pelagic predators which stalk the wandering 'blue fleet' of Man'O'Wars. They are not the only molluscan hunters of these drifting stingers and further along the beach I found a couple of examples, but I'll save those for future posts.
The blue fleet is a remarkable community of creatures. Normally they ply their trade far offshore but as the Physalia blindly drift where the wind blows and all the others follow the whole lot are prone to being blown ashore.
Like many pelagic sea creatures Glaucilla and its close relative Glaucus are not restricted to any one sea area- they occur almost everywhere the sea is the right temperature for them. They float upside down (the photo here is of their belly) close to the surface tension and simply bump into their prey as they drift. They can be mobile if they find themselves stuck- flexing and wriggling in that sea-slug sort of way until free. The blue colour is said to be the accumulated venom from the zooid tentacles. This obviously works as a predation deterrent- beachcombing Silver Gulls carefully avoid them.
So, a carnivorous sea slug which sails the seven seas hunting a dangerous prey- surely that has to be the weirdest thing I found on the beach that day. Not so...

Oysters can save New York!

Architect Kate Orff has a molluscan vision for the New York waterfront. Fascinating stuff.

Molluscivores Part 2: Snail-eating Snakes!

Time for another mollusc-murderer. This week its video of the remarkable snake Pareas iwasakii. These snakes are adapted to hunt meaty forest snails such as this Satsuma mercatoria. The relationship between this predator and prey neatly illustrates the role predators and prey role in shaping each other's evolution. A truly cool reptile.

Mollusc Giant: The Spanish Dancer

The famous Spanish Dancer nudibranch Hexabranchus sanguineus is the current best bet for biggest sea slug. This one was photographed at a shipwreck near the island of Bali, Indonesia. Its 90cm long!

Molluscivores Part 1: Death from the Skies- Snail Kites!

You already know that molluscs are remarkable, awesome, beguiling and generally terrific, but are you aware of just how nifty some predators of molluscs can be? Mollusc POW is about all things molluscan, and predation can't be ignored as a key factor in shaping the evolution of these beasts. So, over the coming months I'll be featuring cool-things-that-eat-molluscs.

First up is the funky, and slightly bonkers Snail Kite Rostrhamus sociabilis, a nimble new-world bird of prey which specialises in a gastropod diet. Living in swamps across Central and South America they prey mainly on the large amphibious snails Ampullariidae. (That is not a typo- this family of snails possess two sets of breathing structures, one for under the water, one for above, so they really are amphibious rather than plain-old aquatic). In Florida the last remnants of the US population of Snail Kites reportedly live almost exclusively on one species: Pomacea paludosa (pictured below thanks to the Pomacea Project).

Snail kites have several morphological adaptions to aid their molluscivorous lifestyle including needle-like talons and that wacky long decurved bill.
I had intended a photo of  snail kite in action ruining a poor little Pomacea's day but sadly all the good ones I could find online are restricted use. If anyone out there knows of a Snail Kite-and-prey photo I can link to then please get in touch.

Mollusc Giant: Gumboot Chiton- King of the slippery tide pool things.

Polyplacophorans make me feel uneasy, but in a good way. Whenever I find one of these armour-plated lumps stuck to a boulder in a rockpool I ask myself 'why don't I know anything about these?' Then I move on to watching the mussels feeding or annoying a whelk (which kind of answers the question- too many other distractions). I did finally get around to reading a little about them recently and I was pretty floored by what I found- it seem, against all the odds, polyplacophorans are amazing!
These beasts, better known as chitons, slide around most of our rocky coasts on their big molluscan foot, breathing with their long gills tucked into grooves in their underside scraping algae up with their remarkable radula (molluscan tongues). Why are their tongues remarkable? Well, the teeth lining them are tipped with magnetite- an iron-based material which is very tough and, importantly, magnetic. Magnetite has been found in various organs in bees and birds, creatures which need to navigate with precision and its speculated that the magnetite deposits they have help them detect the earths magnetic field and use it to help steer their journeys. Why would a little slow-moving mollusc need this biological GPS? Well, chitons have a habit of returning loyally to a the same spot to sit out their low tide exposure so actually finding their way home after a hard tides grazing is pretty vital to them actually. They have a compass for a tongue.
That is very cool, but its just one of many fascinatingly weird features of this group which I'd like to  explore in future Mollusc POW posts.
To get to the point of this post, another of the Mollusc Giant series, lets look at the biggest of all Polyplacophorans; the Gumboot Chiton Cryptochiton stelleri.
Its odd. It looks like the sole of a Wellieboot (AKA a 'gumboot' by you Aussies and Norte Americanos). Its armour plates (known as 'valves' in the trade) are covered in a funky leathery skin. They live in rocky intertidal zones in an arc around the northern Pacific from California to southern Japan. Its huge (for a chiton). It grows to over a foot long and can weight 2kg! They apparently neatly illustrate the difference between 'edible' and 'tasty' so they don't feature highly in human diets. In fact they have few predators- their main pursuer is Ocinebra lurida, a carnivorous marine gastropod which allegedly just nibbles its ample mantle. Being such a big thing it needs more grown-up food than algae so it occasionally makes holes in giant kelp and other seaweeds.
My only complaint about Gumboot Chitons is that the lack of quality photos of these monsters on the web doing chiton-y things. Oh well. Instead here is a good one of a handsome specimen being wrangled by a fearless rockpool-er.

Mollusc Giants- Giant Clams are, well, GIANT!

In the first in this series I thought I'd opt for a beast which is often (unfairly) overlooked when considering the larger invertebrates; the Giant Clam Tridacna gigas.
Its main disadvantage in the wildlife popularity stakes are its general bivalve-y-ness. It has no front or back, no eyes, no face. I personally think that makes bivalves especially intriguing- we really struggle to, er, walk a mile in their shoes as it were. Its just too damn hard to imagine life as a metre long 200kg shelled marine mollusc.
They are deeply weird, but I like that.
They have florid mantle tissue which they extrude from their shells in their daily doings- some of those funky colours are actually symbiotic zooxanthellae living in the clams tissue photosynthesising goodies in exchange for basic nutrients and a home.
They are huge and long lived- they embed in coral but can live for over 100 years in which time the reef can grow around them so that they are completely 'bricked-in' to the coral structure with only the lips of their shell protruding.
Like all bivalves they have an excellent and exotic life history which I will perhaps cover in more depth in future posts.
Giant clams were once common throughout the Indo-pacific coral zone but over hunting and reef decay has taken its toll so now they are unfortunately scarce. I was lucky to encounter a few while diving in Australia's Great Barrier Reef years back. An unforgettable mollusc, and a worthy animal to kick off Mollusc POWs 'Mollusc Giants' series.