The Veliger's a Lively Tar

More than anything, this is a post to promise that I'm not dead yet. Things appear to be ramping up for field and lab season here, and I suddenly have a lab full of baby snails. We've also just had a stream of prospective graduate students through the department, which led to a nice day of showing off my lab to a bunch of folks but also took a lot of my time.

So, instead of a general marine inverts post as promised, BABY SNAILS!

A Crepidula fornicata veliger, about 24 hours after hatching. It's about 300 microns long -- 1 micron = 1/1000 of a milimeter. Photo taken at 100X magnification. Photo credit: A. Cahill

I work with these guys every day and I absolutely love them. Marine larvae in general are beautiful, but I am currently partial to the baby snails. These are called veliger larvae. They have a coiled shell, like they will as an adult, and look remarkably similar to their adult form overall. The one difference is an organ called a velum. It's a large pair of lobes that have cilia around the edge (on the left side of the snail in the photo above). Those cilia beat and allow the snail to swim and to feed (they capture algae and move it to the snails' mouth). The shell of the larva is transparent, so in the picture above you can see the digestive tract as a dark brown squiggly line, and the stomach is the brown blob at the right end of the shell.

A lot of the questions that I answer in my lab have to do with these larvae. Adult snails don't move much, but these larvae have the ability to swim in the water for weeks and can travel hundreds of kilometers along the coast. It's therefore the larval stage that is critical for exchanging DNA and individuals among populations of snails. The larvae are also vulnerable because they are so small. Many researchers are concerned that they will be more impacted by human-caused disturbance (climate change, pollution, ocean acidification) than adults.

These veligers will be a recurrent feature on the blog, because they take up an inordinate amount of my life.

And just for fun, a larval poem by Walter Garstang. It is just one of many that he wrote about many different larval forms. We had our Invertebrate Zoology students interpret bits of it on their final exam last year, because it's full of technical details if you are familiar with gastropod development. If you're not, it's a cute little rhyming poem.

The Ballad of the Veliger (by Walter Garstang)

The Veliger’s a lively tar, the liveliest afloat,
A whirling wheel on either side propels his little boat;
But when the danger signal warns his bustling submarine,
He stops the engine, shuts the port, and drops below unseen

He’s witnessed several changes in pelagic motor-craft;
The first he sailed was just a tub, with a tiny cabin aft.
An Archi-mollusk fashioned it, according to his kind,
He’d always stowed his gills and things in a mantle-sac behind.

Young Archi-mollusks went to sea with nothing but a velum—
A sort of autocycling hoop, instead of pram—to wheel ‘em;
And, spinning round, they one by one acquired parental features,
A shell above, a foot below—the queerest little creatures.

But when by chance they brushed against their neighbours in the briny,
Coelenterates with stinging threads and Arthropods so spiny,
By one weak spot betrayed, alas, they fell an easy prey—
Their soft preoral lobes in front could not be tucked away!

Their feet, you see, amidships, next the cuddy-hole shaft,
Drew in at once, and left their heads exposed to every shaft.
So Archi-mollusks dwindled, and the race was sinking fast,
When by the merest accident salvation came at last.

A fleet of fry turned out one day, eventful in the sequel:
Whose left and right retractors on the two sides were unequal:
Their starboard halliards fixed astern alone supplied the head,
While those set aport were spread abeam and served the back instead.

Predaceous foes, still drifting by in numbers unabated,
Were baffled now by tactics which their dining plans frustrated.
Their prey upon alarm collapsed, but promptly turned about,
With the tender moral safe within and the horny foot without!

This manoeuvre (fide Lamark) speeded up with repetition,
Until the parts affected gained a rhythmical condition,
And torsion, needing now no more a stimulating stab,
Will take its predetermined course in a watchglass in the lab.

In this way, then, the Veliger, triumphantly askew,
Acquired his cabin for’ard, holding all his sailing crew—
A Trochophore in armour cased. with a foot to work the hatch,
And double screws to drive ahead with smartness and despatch.

         But when the first new Veligers came home again to shore,
         And settled down as Gastropods with mantle-sac afore,
        The Archi-mollusk sought a cleft his shame and grief to hide,
        Crunched horribly his horny teeth, gave up the ghost, and died.