Hello readers! Given the exciting morphological progressions my larvae have recently achieved (I’m so proud of them), I’m devoting this week’s post to describing their developmental milestones.
Sea urchin larvae (Strongylocentrotus purpuratus)
The pluteus (sea urchin larval form) morphology has transformed dramatically in the past few weeks. In the first picture we see the pluteus in its late prism stage, when it had recently formed its mouth and gut, and had yet to form its larval arms. In the second picture we see that the pluteus has successfully begun the development of its post-oral arms. Stay tuned--in upcoming weeks we will see posterodorsal arms developing from the anterior of its body.
Sea star larvae (Patiria miniata)
While at first glance the bipinnaria (sea star larval form) may not appear to have undergone significant development in the past few weeks, a closer look shows otherwise. Note how the ciliated band (the oval, outer form of the body) has lengthened and become more curvaceous. By increasing the length of this band, the bipinnarial now has more cilia (cells with whip-like tails called flagellae) to propel food particles into its mouth, aided by its two lengthening pre-oral lobes (the tip of the pointed “hat” on the anterior end of its body). Given that in both pictures the larval stomachs are filled with red algae, it is clear that my bipinnariae are successfully eating. In the first picture we also see evidence (the green substance) that my larvae can successfully defecate!
Phoronid larvae (Phoronopsis harmeri)
In my opinion, the antinotrochs (phonorid larvae) are the cutest of all my larvae (I know a parent shouldn’t have favorites but just look at them waving around their newly-developed tentacle crowns!). I am greatly anticipating observing morphological changes in the antinotrochs. As they continue to develop, they will eventually secrete a tube which allows them to camouflage in the mudflat sediment they reside in.
Looking at these developing larvae, I find it incredible to think that someday these larvae will metamorphically develop into their adult forms as sea urchins, sea stars, and phoronids (a type of worm). Given the dramatic morphological changes marine invertebrates make as they develop from larvae to adults, it is easy to imagine the confusion (and misidentification) past marine biologists faced in identifying organisms at different life stages as members of the same species. Next week, I will elaborate on this issue and discuss how DNA sequencing has dramatically increased scientists’ ability to identify species (and how DNA sequencing has led to the discovery of an incredible number of new species).
“Instructions for living a life./ Pay attention./ Be astonished./ Tell about it.” (Mary Oliver)