A world in a drop of seawater

To see a World in a Grain of Sand
And a Heaven in a Wild Flower,
Hold Infinity in the palm of your hand 
And Eternity in an hour.

-William Blake

We peer through our scopes at these little aliens, one species at a time (if we're lucky). But even when our finger bowls contain a host of different larvae, the world they inhabit is–by design–sterile, clear, and simple. Yet, a drop of seawater contains all our species and more, a world of diatoms, larvae, and bacteria, alive and wriggling with an animus all-too-difficult to capture in an image. Photographer David Littschwager captured this dynamic environment by magnifying a drop of water 25X, and the results are spectacular.

click here for the key 

image credit: David Littschwager, via thisiscolossal.com

Crepidula development

While working with the Calliostoma to spawn, we discovered Crepidula (slipper limpets) attached to the Calliostoma shells. Removing the limpets, we uncovered several stages of the Crepidula development. Brooded by the adults, the embryos and juvenile Crepidula live protected by their parent's shells until they are developed.

Developing skeletal structures

Our larvae are slowly developing morphological complexity, from translucent blobs of tissue to the differentiated subjects below. Each of these guys shows a developing larval skeleton: in Parasticopus, the skeleton is still just a calcified disk in a projection near the anus. For Stongylocentrotus and Dendraster, the skeletal system is far more complex, composed of long spiny arms, and internal buttresses. In particular, Dendraster has a rather striking hinge (above the stomach), while late pluteus of Strongylocentrotus has a web of skeletal plates circling the stomach, just above the developing rudiment.

P. parvimensis (20X)

S. purpuratus (20X)

D. excentricus (5X)

Coelom study buddy

Those elusive coeloms, once so difficult to image, are now taking over the innards of our Patiria miniata. What started as tiny little "blebs" of mesoderm pinched off of the archenteron, now occupy a large fraction of the larva's volume. These coeloms, previous referred to as either the somatocoel/axocoel/hydrocoel or anterior/posterior coelom, flank the esophagus, before joining together in the diminished blastocoelic space. 

P. miniata 1 week post-fertilization (10X)

P. miniata ~2.5 weeks post fertilization (20X)

A larval Space Odyssey

While playing around with different illumination techniques, I stumbled across the sci-fi wonder of the dark-field, a technique which makes every subject look like the cover of an Orson Scott Card novel. Dark-field, which works by focusing only the light scattered by the subject, is a great way to image unstained/living animals. These little living space ships gain an otherworldly aspect, and one can being to admire their sleek design. The long arms of a D. excentricus swing wide, like an x-wing on an attack run while the prominent gut of P. giganteus looks like a giant star-drive, flanked by the twin fuel-tank coeloms. The prismatic colors and shallow depth-of-field make each larvae look simultaneously red and blue-shifted, as if we've caught them mid hyperspace jump. Cool stuff.

D. excentricus (pluteus stage, 10X)

P. giganteus (bipinnarian stage, 10X)

P. parvimensis (early auricularian, 10X) 

S. purpuratus (pluteus stage, 10X)

Schizocardium spp. (early larva 20X)

Rudimentary

Our Strongylocentrotus purpuratus urchin larvae (fertilized 4/1) are on the verge of a radical lifestyle change. An outpocketing of the left hydrocoel (featured in previous posts) is starting to look suspiciously like an echinoderm, pentamerous symmetry and all. This so-called 'rudiment' of the adult organism will soon part ways with the bilaterian pluteus and adopt a sea urchin's benthic existence.

Left lateral view, rudiment circled in red.


 Dorsal views, focused close (top) and far (bottom) to show different parts of rudiment.

All photos taken at 200X under DIC illumination.

After depositing the rudiment, the rest of the larva will swim away to...well, we're not sure where. More on this to come, we hope.

S. purpuratus clone!

When examining the S. purpuratus larvae from April 1st, I noticed a few smaller organisms. The small clones of the larvae appear to be just completing gastrulation (yellow region is the forming gut) and could develop into complete new larvae. The clones are about 1/4 the size of the other larvae and have few of the major structures seen in their more mature counterparts. 

Gulp!

These two motion sequences feature a ten-day bipinnaria larva of the giant sea star Pisaster giganteus capturing (above) and "swallowing" (below) some green algae. Those small, oblong, greenish, hapless cells are Chlamydomonas sp. 
P. giganteus is an indirect developer, meaning that it must feed on plankton as a larva to obtain the energy necessary to metamorphose into a juvenile sea star.

The larva traps its prey using a ring of cilia around its mouth (oral ciliary band), and transfers it to the gut with the help of additional cilia and a sphincter. Coeloms are visible on either side of the esophagus. Ventral view shot at 200X under DIC illumination.

P. parvamensis and the Hydropore

The 10 day old P. parvamesis larva has developed a hydropore, seen on the right of the photo. The hydropore, a small tubule, allows for preliminary gas and waste exchange to the hydrocoel.
The P. parvamensis larvae at this stage have a well developed gut, and in the photo, the mouth, esophagus, stomach and anus can be seen. The ciliary band (not labeled) is primarily around the mouth, to transport algae into gut.

P. giganteus (4.10.14): developing axocoel

P. giganteus (4.10.14), one week after fertilization (left). Both left (L) and right (R) hydrocoel are visible. Note development of hydropore and L axocoel. See sketch (right) for labeling.

Patiria miniata Early Bipinnaria coelom detail

P. miniata 1 day post fertilization. Here the L and R hydrocoel are visible, along with the L somatocoelom.

P. miniata 7 days post fertilization. The gut is stained red from Rhodomonas. Both the Left and Right Hydrocoel are visible (center), as well as the posterior coelom (top right), situated over the gut.

Welcome to the Course Blog! Check out this "Mystery Animal"!

Hey guys,

Here's a video that was captured during the course last year. …What do you think this beast is?

HINT - it is the metamorphosed juvenile of a species we'll be studying this Quarter. Any guesses*? There's a Lowe Lab Latte in it for anyone who can tell me at the beginning of lecture on Tuesday!

*Remember - when you post, please describe what you're showing us (species, life history stage, etc.) so you don't leave us all guessing!

Happy blogging,

~nat