Look closely at any odd piece of kelp, and the little white patches you'll find are probably these guys, entire colonies of bryozoans, each little cell a cloned zooid. Like little vampires they rest in tiny coffins, bursting out to feed upon unsuspecting phytoplankton. Unlike vampires, but in keeping with the general invertebrate theme of "confuse the hell out of taxonomists," some bryozoan larvae look like translucent, fringed beanies (Top). These odd beings, called "cyphonautes," are the planktonic larvae of a few bryozoan genera, such as Membranipora membranacea (below).
sources: Hayward, Peter J., and John Stanley Ryland. Cheilostomatous Bryozoa: Notes for the Identification of British Species. Field Studies Council, 1998.
I had some fun with my late-stage Patiria brachs the other day, and found this guy trucking along. Normally these larvae orient orally/aborally to the slide plane, but this one was comfortable in a kind of 3/4 perspective, swimming along. The bright orange at the top is the larval stomach, surrounded by the forming juvenile skeleton. Oriented ventral side down (left), the stomach is at the top, and the brachiolarian complex at the lower right. This video showcases the settlement behavior/orientation of pre-metamorphosis Patiria larvae, which use the adhesive palps of the brachiolarian complex (the bright blebs of tissue) to secure themselves to the substrate while the juvenile body adsorbs the larva. This larva is 3 weeks old, and was rudely removed from its happy algae-encrusted home for this video.
We fixed this poor guy just before he finished lunch! In this image we can see the algae, Rhodomonas lens,autofluorescing in the esophagus of this Patiria miniata brachiolaria, (red) and also the fine rings of smooth muscle that contract to push food into the gut (the green is filamentous actin, stained with phalloidin). Spectacular! Now one of you guys just needs to image it on the confocal...
P. miniata stained with Phalliodin to label F-Actin (green). Zeiss Discovery.V12 stereoscope, 1.5x planApoS lens, 120x
Two individuals of Dendraster excentricus are shown here metamorphosing. This is real time footage, and it is amazing how quickly the metamorphosis occurs. In the early stages, you can see the tube feet moving around inside the larval body before breaking through and opening up the larval body, allowing the juvenile to completely emerge. The first half of this video shows a lateral view of the metamorphosis, and the second half gives an aboral view. After metamorphosis, the juvenile walks away, carrying some remnants of the larval body along. The larval body and skeleton quickly deteriorate after metamorphosis.
Sea squirts, or ascidians, are some of our closest invertebrate relatives. They are classified as chordates because they develop indirectly through a 'tadpole' larval stage. Ascidian tadpoles have notochords, dorsal nerve tubes, and pharyngeal slits just like their vertebrate amphibian counterparts. Not that they're phylogenetic neighbors.
Development and its results in ascidian versus amphibian larvae are dramatically different. Ascidian tadpoles are lecithotrophic: the mouth is closed off from the gut, and the larva depends on maternally furnished yolk as fuel through metamorphosis. When an ascidian tadpole finds a place to settle, it anchors with an adhesive secreted from its anterior papillae and begins to absorb its own tail, notochord and all.
You can see the middle part of that process here, in a video of Ascidia ceratodes (fert. 5/6/14.)
The ascidian might take three hours or so to absorb its entire tail. A few days later, its mouth will open and filter-feeding begins!
Thanks to http://chordate.bpni.bio.keio.ac.jp/faba2/2.2/developmental_table.html and Strathmann for an idea of what to expect in the development timeline.
Video is 30 s interval time lapse shot at 100X under DF illumination.
Our batch of S. purpuratus, spawned on 4.1.14, have finally begun metamorphosing! During the pluteus stage, the larvae forms a hydrocoel, followed by both the axocoel and somatocoel, which soon merge to form the rudiment, the basis of the adult body plan. The rudiment continues to develop throughout the larval stage until metamorphosis, whereby the rudiment emerges from the sides of the larval body as a juvenile.
Pluteus with rudiment, circled in red. Photo taken 5/6/14.
Juvenile after metamorphosis. Photo taken 5/13/14.
Spawned on 4.28.14, our C. ligatum larvae have begun to hatch! Developing through the trochophore stage within their egg capsules, the larvae emerge as veligers. The veligers of C. ligatum are non-feeding and instead subsist on stored yolk throughout their development. Hopefully, these veligers will soon settle and metamorphose into juveniles!
Veliger still encased in its egg capsule, on the brink of hatching. Imaged in dark field.
Hatched veligers. Imaged in dark field (top) and DIC (bottom).
On Thursday, I was admiring a very unusually shaped late stage Dendraster. I could see that the entire body was the juvenile, and the larval body was completely deformed. The juvenile's tiny tube feet could be seen moving about within the larval body, and as I watched, the first of the tube feet broke through the larval body. Tube foot after tube foot followed until the juvenile had almost completely emerged from the larval body. I rushed to get it under the video scope, but only caught the tail end of the emergence. In this video, you can see the juvenile about 1 minute after the initial emergence, and beneath it, the remains of the larval body can be seen. The translucent spikes beneath the juvenile are the fragments of larval skeleton. The entire emergence probably occurred over the period of about 2 minutes. The juvenile was then able to begin cruising around the substrate, though some of the larval body was still attached dorsally.
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.
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.
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.
Those elusive coeloms, once so difficult to image, are now taking over the innards of our Patiriaminiata. 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.
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.
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.
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.
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.
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), 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.
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.
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!
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hydropore.JPG)
