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).
